Intermittent cluster gauges and blower, multi-year issue

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#16715 Closed 1999 Chevrolet Silverado 1500 3dr Ext Cab, NBS public

Hi, It’s been a few years, maybe 5, since I first posted the intermittent problem in my 1999 Silverado. I can’t find my original Q/A on your website, and probably no longer have the email address I was using at the time. Back then I removed the dashboard and looked at two grounds G203 and G201 maybe? They seemed fine. Thanks for your help in that regard. I didn’t do any more trouble shooting. It comes and goes. If I recall correctly, I may not have even showed up for a 12+ month stretch.

However I believe I recently stumbled upon the cause! It’s been acting up often these past two months so I started looking into it. I removed the knee bolster which exposed the lower instrument panel frame. In a port/hole in the frame near my left knee there is a thin yellow wire. Giving it a quick light giggle caused the instrument cluster to go through the ‘boot-up’ phase. After that, everything worked again!

I’ve been driving it now for about 1000 miles during which the gauges/blower have shut down about 10 times. Each time, all I needed to do was to lightly giggle/touch the yellow wire. The IC would re-boot and everything would be working again. But I’m not sure what the actual problem is. I noticed two things though.

First there is a heavy gauge red wire going into a connector. The red insulation is blackened near the connector as if the insulation overheated.

Second, the thin yellow wire (the one that I giggle) has a VF4-45F11 Siemens relay splice into it with crimp connectors. I don’t know the role or name of the relay. It’s a factory relay, I’ve owned the truck since new. I can’t find that relay on Rock Auto for my truck. If I remove the relay, the engine will not crank, but the IC boots and operates normally. The relay has a metal flange for bolting onto to something, but it is not bolted any to anything, nor does it show signs of ever being attached. There is an orange wire coming out of terminal 86, but the other end is not connected to anything.


Most likely you are dealing with some sort of aftermarket add on. Anti theft, remote start or alarm. Most likely installed by the dealership you bought the truck from.

The discoloration on the red insulation is from heat build up at a faulty terminal crimp.

Can you upload a picture?

I guess there are three issues, some may be related though. Attached are 2 photos. Thanks
1) intermittent cluster gauges/odometer/blower
2) overheated heavy red wire (photo) (could be orange)
3) mystery relay

The data sheet and the spec sheet for the VF4-45F11 are here:

The relay is wired:
30 heavy white with black stripe
85 red
86 orange (other end is loose)
87a black
87 not used

There is an external diode connecting the orange and red wires.


The small yellow wire should run from the ignition switch to the crank fuse. It should be powered when the ignition key is in the crank position. I would recommend removing the relay and harness. Then reconnect the two ends of the yellow wire back together.

The orange wire should come from the ignition switch to the back of the interior fuse box. It supplies power to several things including the instrument cluster and the HVAC system.  The best repair would be to replace the fuse box and the orange wire with a new terminal. A lessor repair would be a new wire and terminal lead. Also clean the terminal on the back of the fuse box.

This is a similar repair I made a few years back.

2003 Chevrolet Silverado, Blower Does Not Work On Any Speed

While I can understand the relay diagram, I can’t make sense of any function especially with the external diode on the harness. And I have no idea who may have installed it.

I looked at schematics in the GM Service Manual, and they’re consistent with what you said — that the yellow wire normally routes directly from the ignition switch to the crank fuse. As such, the yellow wire goes to the correct terminal/connector on the back of LBEC. I’ll see about tracing it up to the ignition switch.

So I think I’ll first remove the relay like you suggested, and leave the overheated orange wire alone for the time being. In the meantime, I’ll see about buying an assortment of terminals compatible with my truck so that I’ll have them on hand to repair the overheated wire should the intermittent issue continue.

I traced the yellow wire back to the ignition switch so I was pretty confident the yellow wire was in fact the one in the Service Manual schematics and end connector views. So I cut off the mystery relay assembly at the crimps, just on the OEM side. Then stripped, soldered, and shrink wrapped the OEM yellow wire back together.

I then plugged the terminal back into C on C3 at LBEC. But as you can see, I did it the dufus way and had to pull out the blue lock clip, needle the tiny black retaining tab, then pull the yellow terminal back out, then reassemble.

The tiny black retaining tab for the terminal on the overheated large orange wire broke yesterday, I suppose due to heat stress. The others have been fine. Truck starts and runs fine. And the blue lock clip is kind of a back up retainer, but I’d like to replace the connector, C3. Does it have a part number?


Years ago, new and used car dealers would install an anti theft device as an extra feature on all vehicles they sold. In addition to the relay that you have there would usually be a plastic housing with a slot and several wires attached. A circuit board “key” would be installed in the slot. Without the “key” the starter and sometimes the fuel system would not work, keeping the vehicle from being stolen. I have removed hundreds of these system after they have failed.

The diode that is installed in the relay harness connector can have two functions. First to insure a quick disengagement of the relay and second to suppress any voltage spikes when the relay coil collapses from being turned off.

At rest terminals 30 and 87a are connected to each other. When the relay is activated terminal 30 becomes attached to terminal 87 and in your case the engine would not start.

Since the white/black wire and the red wire are attached together with one yellow wire that means that half of the yellow wire comes from the ignition switch. The yellow wire half that is attached to the black wire goes to the crank fuse in the fuse box.

If you were to apply a ground to the orange wire the starter would not work. Take the ground away and it would start again. So they were using a grounding device  to disable the starter. Also if you were to just remove the relay it would not start.

They easiest repair for the burnt orange wire situation would be to buy a used fuse box with the harness connector and about a foot of wire. Remove all terminals from the replacement harness connector except for the orange wire. Transfer the good terminals from your original connector into the replacement. Then splice in the orange wires.

Keep in mind that the burnt wire got that way from fairly high heat build up and left unattended you could have a fire.

Thanks for all your help. I have a couple of other questions, in the meantime this is heading your way, to Sparky’s Answers P.O. Box 2006 Moncks Corner, SC 29461-2006

Let me know if the address is not correct.


It is the correct address. However, I forgot it was even listed.

I no longer have an account under that name and therefore no way to accept a check or money order.

Sorry for the inconvenience. I have  taken the address down from the Support/Donation page.

If you have more questions about the relay in your truck feel free to continue using this thread. If you have questions on a new topic please start a new thread by asking a new question.

Ok, well it is on the way to Box 2006 as of yesterday afternoon. The return address on the envelope is correct. If you mail it back to me I can probably get my money back from the bank (never done any money orders in my life), then we can figure some other way for me to make a donation. Do you have online sales? for example Amazon Seller, or Ebay Seller or Etsy Seller, or …? Also feel free to see if your previous financial institution will honor it. Might be feasible if it’s a local branch that you can walk into.

The local pull-it-yourself junk yard wants $51 for a fuse box with harness, or $28 for a bare fuse box. Not sure exactly how much harness or how little harness they mean, and I didn’t see any. In their online price list they don’t have an entry for simple electrical connectors.

I found the part number for the connector body LBEC C3 as 12193930. A local dealership doesn’t have that GM number in their system, nor does There are third partys that sell new pigtailed 12193930s online starting at $20 shipped. Not sure the quality in those 3rd party connector body, Metri-Pack terminal and the crimping, so I may end up back in the same boat of an overheated large orange wire.

Do you think it over heated due to the dealership’s temporary install of the anti-theft relay? For example, the the OEM crimping may have been sufficiently low in resistance to carry the OEM current load, but too high of a resistance to carry the additional current drawn by the antitheft ‘device’.


I will see what my bank will do.

If you can pick the part yourself, then you should be able to get enough wire to make the splicing easy.

I too, would be leery of the 3rd party replacement parts. Likely very cheap components.

Mouser Electronics at is a good source for the components that you need. The connector body is $5.62 + shipping. They would also have the terminals you would need.

The only issue is that you will need to invest in a pair of specialty crimping pliers. These are a pair that I use that don’t cost too much.

The relay by itself would not cause the issue since the yellow wire circuit only works another relay anyways. Maybe a total of 1 amp load and only while cranking. The over heating issue is likely due to a problem with the HVAC system. More specifically the blower motor is used on higher speed for an extended time. Could be driver preference, dirty cabin air filters, leaking door & window seals, improper refrigerant charge and etc.


I’ve been reading online about relays and came across a page that says

“The diode will always be installed in the relay with the stripe on the diode body facing towards terminal 86 (reverse biased) and it is important that +12V is connected this terminal (with 85 connected to ground) or the diode could be damaged.”

The diode in the mystery relay from my truck is opposite. The stripe is on the red terminal, 85, which is the ignition switch side of the coil.

Here is the page:

Here is the longer snippet about the diodes:

“When voltage is removed from terminals 85/86 and the coil is de-energised, the magnetic field that has been created around the coil collapses rapidly. This collapse causes a voltage across the coil in the opposite direction to the voltage that created it (+12V), and since the collapse is so rapid the voltages generated can be in the order of several hundred volts (although very low current).

These high voltages can damage sensitive electronic devices upstream of the +12V coil supply side, such as control modules in alarm systems, and since it’s common to take low current alarm output signals to energise relay coils, equipment damage is a real risk.

Using a relay with a diode across the coil can prevent this damage by absorbing the high voltage spikes and dissipating them within the coil/diode circuit (this is known as a blocking or quenching diode). The diode will always be installed in the relay with the stripe on the diode body facing towards terminal 86 (reverse biased) and it is important that +12V is connected this terminal (with 85 connected to ground) or the diode could be damaged.”


The article is written in reference to ISO standards and if you read closely it refers to a diode installed internally and not externally of the relay.  Electrically the diode may be installed in either direction and the wiring adjusted for the proper circuit control but if it is internal to the relay it will not meet ISO standards and therefore could not carry that designation.

So, if an engineer/manufacturer uses an ISO rated relay with a built in diode they must adjust their design/layout to meet the design of the ISO relay.

If they use an ISO or non ISO relay without a built in diode they may wire it either way that makes them happy.

They could also designate a non ISO relay with a built in diode that is installed in reverse of the ISO protocol and wire the harness accordingly.

So, it is kind of the wild west out there unless you see a mark designating what standard is being followed. That is why I often use the saying “test don’t guess”.

Hope this makes sense.

Thanks, I didn’t pick up on it referring to an internal diode.

Since removing the mystery relay from the yellow ign-crank wire, I’ve put 500 miles on the truck. The intermittency of gauges/odometer/blower has not reappeared. Given how frequently it was surfacing these past two months, it seems solved. But it is not certain. Over the past number of years, there have been periods of months on end, possibly a year or more, without the issue surfacing. Also I don’t have a theory on how the mystery relay could have been causing the gauges/odometer/blower to intermittently not work. And lastly, because you have found that repairing the overheated wire fixed similar issues.

I plan on repairing the overheated wire and replacing the cracked 12193930 connector on my truck.


I can guarantee that the only link between the relay that was removed and the cluster/blower issues is the coincidental movement of the loose connector on the orange wire.

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