How to Replace a Wiring Harness Connector

Just about anyone with basic mechanical skills can splice in a new harness connector. However doing it so it fits properly and looks good is an entirely different thing. On this coolant temperature sensor harness replacement I started by removing the factory tape the finishes the split loom installation.

The split loom needs to be pulled back far enough so that enough wire is exposed to complete the replacement. On this one I took the loom completely off.

I cut and spliced one wire at a time. I prefer using un-insulated splice or butt connectors that have brazed seam that will not split apart.

I also use dual wall heat shrink tubing with a 3:1 shrink ratio and a meltable sealing liner. Also notice that the joints are staggered to prevent a knot of splice joints that cannot be made into a smooth harness. A little heat from a small butane torch. The flame is set very low and I always make sure there is nothing flammable around. A heat gun can be used as well a a small lighter.

I slid the split loom back into position except for the last inch or so.

To start the process of finishing the end, I wrap the wires a couple of times with tape. The tape is positioned where the end of the loom will be.

I pull the roll of tape out and hold it straight where the slit is in the split loom. I then slide the split loom fully into position around the tape as shown below.

Then I finish with a couple of more wraps around the outside of the split loom.

A nice neat wiring harness repair that will last a long time.

It also looks like a factory harness when completed.

The repaired harness plugged back into the coolant temperature sensor.

2000 Chevrolet Cavalier, P0118 Low Coolant Temperature

This 2000 Chevrolet cavalier came in with the SES light on and a code P0118 stored for low coolant temperature among other problems. A quick scan found that the coolant temperature was at -40 degrees F. The outside temperature is in the mid 70’s.

I found the coolant temperature sensor broken and the harness connector damaged.

I installed a jumper wire between the two wires to check the wiring and the computer out.

The temperature reading went to 303 F. That told me that the wires  and the computer were all okay. If it had changed to anything significantly lower than 300 F I would have had to do some testing on then wires to determine if there was a wiring problem or an internal computer issue.

I removed the old broken sensor and installed the new one.

I spliced in a new harness connector for the coolant temperature sensor.

Applied heat to the heat shrink tubing.

Everything installed and reconnected.

Now I have the correct coolant temperature reading. The engine had been sitting overnight before I got to it.

2002 Chevrolet Malibu, Power Outlet Not Working

This 2002 Chevrolet Malibu came in with a simple enough complaint. The power outlet in the dash did not work. Simple enough. I went to fuse number 34 in the underhood fuse box to check the fuse.

Why is there a 2 amp fuse when there should be a 20 amp fuse? Why is it sitting in there crooked? What is that black stuff at the bottom of the fuse?

The fuse box legend showing the fuse in question is fuse number 34.

And the complication. Out of desperation to remain connected to the world. The driver found the blown fuse for the power outlet (cell phone charger port). The only fuse she had left was a 2 amp fuse. It blew immediately. Since “the fuse was too weak” her and her boyfriend decided to wrap the fuse terminals with a single strand of copper wire.

Turned out to be a $2000 fuse by the way. Since she did not have the money for repairs and the only thing that was not working was the power outlet, we decided to install a new power outlet and create a new power source circuit for it. From past experience, I told her that we should not even touch the harness that had been damaged, except to clear off the obvious burnt ends. We could cut them without disturbing anything else.

She has been driving the car for 6 months now without any issues. It had 260,000 miles on it when it came in my shop. Another reason to not sink a lot of money into this repair.

1998 Oldsmobile Silhouette, No Run Condition

This 1998 Oldsmobile Silhouette was towed in with the complaint that the engine would not run and fuse number 18 in the underhood fuse box was blown. The fuse would blow as soon as the key was turned on. This fuse supplies power to the fuel injectors.

The “Ignition Main” relay.

A little looking around and I found this wiring harness rubbing on the cooling fan.

Several wires were cut and touching each other and metal. I isolated the damaged wiring and jumped the pink wire back together to make sure the short was gone and that the engine would run.

That was the fun part. I still had to do the grunt work of repairing the harness and securing to back to the factory holder. Some how I did not have or lost the pictures of the rest of this post. Hopefully you get the idea though. Repair one wire at a time. Wrap the harness and add split loom to protect it. Then secure it with clips, fasteners and ties.

2001 Pontiac Grand Am Low Blower Speeds Do Not Work

This 2001 Pontiac Grand Am came in with the complaint that the low and medium 1 blower speeds do not work. Since the higher blower speeds work fine, the diagnosis will begin with the blower resistor assembly.

The blower resistor is under the passenger side of the dash.

The lower dash hush panel needs to be removed.

A couple of 7 mm headed screws.

A push pin.

The outer underdash cover comes out.

Next the inner cover and duct assembly.

Since the blower was working on the higher speeds, testing is as follows.

Key on.
Resistor disconnected.
Blower switch set to low. There should be battery power on the yellow wire.
Blower switch set to medium 1. There should be battery power on the tan wire.
Blower switch set to medium 2. There should be battery power on the light blue wire.
Blower switch set to medium 3. There should be power on the purple wire.
Blower switch set to high. This signal is sent on an orange wire to the blower relay in the underhood fuse box.

If the signal is sent and the relay and remaining wiring is working correctly, the blower motor will work. Assuming of course that the motor itself is good and the is a proper ground at the black wire, terminal “A” of the blower motor connector. High blower power is delivered on the purple blower motor wire, terminal “B”via the blower relay normally open contacts.

The dark blue wire at the blower resistor goes to the normally closed contacts in the blower relay in the underhood fuse box and then on to the purple wire at the blower motor. All of the lower blower speed signals go from the blower switch, through a  resistor or up to a total of all four resistors before going to the normally closed contacts in the blower relay. The signal finally arrives at the blower motor on the purple wire.

If the blower motor does not work at all testing should start at the blower motor and be done with all harnesses connected.

There are two screws with 5.5 mm heads that hod the resistor in place.

The old design resistor with a short green circuit board.

The new design longer blower resistor with a black circuit board.

I reassembled this one and gave it back to the customer.

2003 Dodge 2500 Pickup, Blower Not Working

This 2003 Dodge 2500 pickup came in with the complaint that the blower would work sometimes and luckily for me it was not working when it came in. A quick check at the blower motor revealed no power at the two wire connector. After looking at a wiring diagram, I did a quick test of fuse #4, 40 amp in the underhood fuse box. It was good. The next step was to check the ignition switch.

I started by removing the tilt handle from the steering column.

It just pulls towards the driver’s seat  and slides off of the aluminum lever. Moderate force is needed to pull it loose.

Next there are three torx screws that have to be removed from the lower steering column cover. I think they were T20’s.

With the lower cover removed the upper cover lifts off of the steering column.

The red locking bar has to be slide out and then the built in locking tab has to be depressed to unlock the lower half of the harness connector.

At the top of the connector for the ignition switch the white slide lick has to be lifted. During the lifting process the connector will be disengaged from the switch.

The inside of the harness connector. The bottom two terminals are burnt. It looks like a shadow in the picture but it is not.

The wiring into the SRS clock spring has to be disconnected before before the screws for the tilt lever assembly can be removed and the assembly dropped out of the way.

I use a hooked tool to depress the locking tab on the top side of the connector.

Then remove the two screws that hold the tilt lever assembly to the steering column.

The tilt lever assembly positioned out of the way and slide the old switch out.

Slide the new switch in and reassemble the steering column parts.

The burnt terminals on the old ignition switch.

The four prongs on the blue terminal retainer have to be pushed in to release it from the harness connector body. It takes several steps to get it released.

Using an angled pick I removed the good terminals from the old connector and installed them in the new connector.

I know it may seem strange but I used the smallest wires in the supplied kit to replace the two burnt wires. However I added a relay to carry the load of the blower motor and now the switch just has to carry the load of the relay coil. About .5 amps.

The relay installed in the wiring under the steering column.

The new harness connector with all of the wiring installed.

To connect the relay:

I installed a new smaller blue wire with terminal attached at terminal 1 of the ignition switch. I connected the original pink/black wire from terminal 1 of the ignition switch and terminal 30 of the relay. At that splice connection I also tied in the newly installed wire from terminal 1 of the ignition switch.  This three way splice can be seen at the splice on the red relay wire.

I connected the dark green wire from the vehicle harness to terminal 87 (purple wire)of the relay.

I installed a second new small blue wire and terminal assembly into the ignition switch connector at position 8. I then connected terminal 86 (yellow wire) of the relay to the new wire/terminal (small Blue wire) installed at position 8 of the ignition switch harness. You can barely see that splice behind the splice connection on the large purple wire splice from the relay.

Terminal 85 of the relay was connected to a good chassis ground.

I secured the relay to the bracket with a wire tie and installed a rubber cover over an exposed point on a mounting screw to protect the wiring from accidental damage.

Everything tied down and secured. All that was left was to trim the wire tie and reassemble the steering column and the under dash covers.

Again my reasoning for installing the relay was to let the relay carry the heavy electrical load of the blower motor. The genuine Mopar ignition switch and repair harness kit costs in excess of $200. The relay and it’s harness connector is about $40. In reflection I would probably use an less expensive aftermarket ignition switch, since I was taking the load off of the ignition switch itself anyways.

2000 Pontiac Sunfire, Odometer Reads Error

This 2000 Pontiac Sunfire had multiple dash problems. among which were most warning lights on, erratic gauge operation,the odometer read the word Error and sometimes the engine would not start. My first thought was a faulty instrument cluster because that was where all of the problems were centered.

A feeling is not good enough so I set about doing some testing. I wanted to check codes and data but I found that there was no communication with any module in the vehicle.

After looking through wiring diagrams I realized that the BCM was the hub for communication for all of the modules in the car. The BCM is located under the driver’s side of the dash at the left kick panel area.

I strongly recommend looking at wiring diagrams and component locators before doing any of these tests. It also requires a familiarity with terminal removal and safe testing practices. with live wiring and computer modules.

The purple connector at the BCM in this car is the C1 connector and the communication line between the BCM and the Radio is on terminal B8.

To make testing and identification easier I wanted to remove the terminal locking comb. There are locking hooks on either end of the retainer. Once unhooked the retainer can easily be removed.

I used a special terminal release tool to unlock the terminal and pull it from the connector.

I also went to the C2 Connector, light blue and removed the locking comb retainers.

With the retainers removed it was much easier to see the terminal designations on the plastic connector body. All wiring involved in testing the computer data lines are purple wires.

Terminal B7 connects to terminal 2 of the DCL

Terminal B8 connects to terminal 59 in the C1 connector at the PCM

Terminal B9 connects to terminal “L” of the IPC

The SRS and EBCM are linked to the communication lines through the IPC and the PCM respectively.

In testing I connected terminal B7 to terminals B8 & B9 of connector C2. Communication was restored to all modules. This only left a test between terminal B7 of the C2 connector to terminal B8 of the C1 connector. This test did not restore communication to the radio.

I needed to confirm that the problem was either in the radio or in the wiring between the radio and the BCM. With the glove box opened the two screws at the right side of the center dash panel could be removed.

It was much easier to remove the lower screw by unhooking the right side hinge stop on the glove box door.

Once the two screws were removed the center panel will slide to the right and can be manipulated off of the dash. There is supposed to be a plastic peg at the left side of the panel, but it appears that someone else has been here, because the plastic peg has been replaced by a screw.

With the trim panel removed I went about removing the screws that held the Radio in place. Phillips headed screws, more evidence that someone else has already been here.

DSC05775

And there it is! I had already discovered that the Radio did not work either and this is the obvious reason why. A little bit of tape on the exposed wiring.

Communication has been restored to all modules.

I did a class 2 DTC check, found and cleared all trouble codes, then started and ran the engine.

No more problems except for the obvious missing Radio.

Can you believe 237,000 miles on this little Pontiac?

2002 Chevrolet Tahoe, Fog Lights Do Not Work

This 2002 Chevrolet Tahoe had several complaints and this one is no fog lights. I connected my Tech 2 scan tool and checked some basic functions and found that the scan tool could turn on the fog lights. There was a codes stored for a park light malfunction. I checked wiring diagrams and found that there is a control circuit for the fog lights that is powered by an interior park light fuse. I located the fuse in the driver’s side interior fuse box. I am pointing to it in the picture below. It was blown. I tried another fuse and it blew as soon as the park lights were turned on.

To make my life easier I installed a fused jumper wire into the fuse box. This allows me to use cheaper fuses or a circuit breaker while testing.

My fused jumper wire with a resettable 10 amp circuit breaker installed.

In reviewing the wiring diagrams I found that there were quite a few interior park lights powered by this one fuse. I went to several locations and disconnected harnesses to isolate the short. This vehicle had been stolen and the interior gutted. At least two body shops have been involved in putting this Tahoe back together, so who knows what I will find.

There is a junction block under the driver’s side of the dash. There is a plastic nut that holds the cover in place.

I looked for and disconnected any harness connector that had brown wires in it. GM has used brown as the wire color for park lights for as long as I can remember. No change in the short when I disconnected the lower harness.

There were a lot of  connection points in the passenger side junction box, located behind the dash end cover.

I disconnected one at a time and  still no change.

I went back to the driver’s fuse box and found one harness with brown wires in it and sure enough the short went away.

I disconnected the driver’s side power window switch and reconnected the harness in the fuse box. The short was gone. Connected the driver’s power window switch and the short returned. The diagnosis should have been a shorted driver’s power window switch but in the end it was not. It was marked in a written label that it was for a 2002 Escalade. I saw where there were several small brown wires in the power window switch wiring. On a hunch I looked at the rear switches and realized they were a different design from the front switch. I unplugged both rear power window switches and reconnected the driver’s switch. The short was gone. Connecting either rear switch would blow the fuse.

I got with the body shop that sent this Tahoe to me and informed them that we had mismatched parts. We decided to order all new power window switches by the VIN. It turns out the front switch was correct for the truck and the rear switches were for a 2003 or newer truck.

With the correct switches installed and a new fuse the fog lights worked as designed. As a little added information. The switches with the flat rocker design are just that. The switches with the lever type switches are driver’s and passenger side door modules, DDM & PDM. The key difference is that a new DDM or PDM will not work out of the box. It has to be programmed to the vehicle using GM’s TIS2Web programming software.

2004 Nissan Maxima, Transmission Will Not Shift

This 2004 Nissan Maxima came in with the complaint that the transmission would not shift properly. The customer stated it felt like the transmission was starting in a high gear. I really did not want to work on this vehicle as the customer informed me that the engine and transmission had both been replaced with used parts. You just never know what you will run into when going behind someone else. First the code checks.

Code P0335 stored in the PCM. although the customer had not complained about it, I had noticed that there was an extended crank time before the engine started.

The TCM had a code P0726 stored for a CAN Failure system. In case you were wondering CAN stands for Controller Area Network.  This means that there is a communication problem between modules.

With the key on and the gear selector in the manual shift position the gear indicator in the instrument cluster shows that the transmission is in the 5th gear.

I wanted to do a little research, in that I have never seen a code P0726 before and I wanted to know a little bit more about it. I found that there are some real world anomalies with the factory diagnostic procedures. The TCM is supposed to use a crank sensor signal along with other data to determine shift patterns. The real world has found that cam sensor signals are also involved with this process. The engineers it seems did not plan on this or they did not inform the service information writers about it. Since I did have a crank sensor code I decided to start there. The crank sensor is located at the bottom center of the engine just below the flywheel area.

Everything looks okay here or does it?  Kind of strange how the end of the connector looks like it is lined up perfectly with the edge of the sheet metal shield. A gentle pull revealed that it was not fully seated.

Could it be that it was that simple. This vehicle had been to two other shops before arriving at mine. Using a pry bar, I straightened out the sheet metal shield.

Then installed the connector until the lock snapped into place.

Of course while I was looking around at the problem I noticed quite a few things out of position.

Gee, you think a wiring harness laying on an exhaust pipe might cause some problems?

It amazes and worries me that someone can actually get an engine and or transmission in and out of a vehicle and leave something like this a mess. I had to round up a few bolts and finish installing a couple for brackets and heat shields. Then reroute the oxygen sensor wiring so that it would not be laying on the exhaust.

It does not look too bad now but I informed the customer that the engine installation needs to be gone over to make sure nothing else is loose or not installed.

Now the shift indicator shows that the transmission is in 1st gear. Both the PCM and TCM codes are now gone. The engine also starts as it should.

This one will be back in a few weeks to finish going over the wiring under the hood.

2000 Buick Century BCM Will Not Communicate

After repairing a poor connection at the DLC on this 2000 Buick Century, click here to see , I moved on to the bigger problem of no communication with the BCM and no crank condition.

I went back to the splice pack under the driver’s side of the dash and located the purple wire, terminal “A” and the light green wire, terminal “M”.  Using a jumper wire I connected the two wires. Then I connected my ohm meter to the purple wire at terminal 2 of the DLC connector and to the light green wire, terminal “A8” of the BCM C2 connector. I disconnected the BCM before testing the circuit to avoid feedbacks. There was no problem with the data line between the DLC and the BCM. Continuity was good and there was no short to either power or ground. I then proceeded to check power and ground inputs to the BCM. All were okay. The diagnosis is a faulty BCM. Including the data line there are 11 circuits that should be tested for problems. Too many to put in this repair. If you are attempting this diagnostic routine I strongly suggest looking at a wiring diagram in your shop data base or buying a subscription from Mitchell or AllData.

With the BCM reconnected and my jumper wire in place, I again checked for communication with the BCM. No communication, diagnosis of a faulty BCM.

I put the shorting bar back in the splice pack and checked all other modules for communication problems. There were no other problems.

By the way these modules are available as a rebuilt unit form ACDelco and they are fairly inexpensive.

There is an expensive snag in this repair though. A replacement BCM cannot be installed without a Tech 2 scan tool. At this time it is the only scan tool capable of performing a BCM Setup. In the BCM menu there is a section for Module Setup.  A VTD Relearn also has to be performed. I used the TIS2Web GM software to perform this function.

There are two lines of setup functions, BPP (brake pedal position) and SDM (sensing & diagnostic module, airbag system) primary key in BCM. Codes in the SDM have to be cleared before this step will work. Sometimes the procedure will clear the codes and sometimes it won’t. Just easier to clear them first.

In the service programming system the VTD (vehicle theft deterrent) program is uploaded to the replacement BCM and you are instructed to wait ten minutes. At the end of the upload you should be instructed to turn the key off for at least five seconds. After that period the engine should then start when you try to crank it.

I should note that on this particular vehicle the BCM Setup would not work until the VTD was performed. I do not know if it is me or not but I think GM changes the routine. It seems like the order of programming events is never exactly the same. Of course it is very rare that I am programming the exact module in the exact car on the same day.  More than likely it is just my mind not keeping up.

The setup procedure has been started.

Now it is completed. It really is not that hard but you have to have the scan tool and TIS2Web programming subscription to replace a BCM.