This 2006 Toyota Tundra came in with the complaint that the power windows and air conditioner did not work. The customer had stated that the battery went dead a couple of times and he would just jump it off. The last time he changed the battery.
I was pretty sure one of the multi fuse link assemblies would be damaged in the underhood fuse box.
I guessed that it would be the black one because it had two visible cables attached to it.
Sure enough no power to one of the cable connections as shown below.
I connected one of my heavier duty in line fuse holders into the system for testing.
I now had power and the fuse did not blow. My thinking is that someone had hooked jumper cables up backwards at some point and blew the fuse.
I decided to connect by charging system analyzer up and check the amperage going through this circuit.
When I first checked it, the reading was 80 amps. It settled down to 59 amps by the time I got the picture.
Just to show the relationship between amps and heat I also took a temperature check of the fuse and fuse holder. The peak was 158° F.
The fuse itself was easy enough to change; one bolt, one nut and it pulled out.
I did have to use a pair of pliers to get it released initially.
I had not paid a lot of attention to it but there is a 7.5 amp fuse that should be removed at the end of the fuse assembly. One side of it is still attached to the fuse assembly in the next picture.
The new fuse assembly on the left and the old one on the right.
The blown fuse in towards the lower right hand corner. It is horizontal and clearly blown.
I lined the new assembly up in the fuse box and firmly pushed it into position. It has to be fully seated in order the get the screw in without cross threading anything.
Installed the cable and nut on the stud.
Installed the 7.5 amp fuse at the end of the assembly.
I had to check the remaining fuses, clear codes and finish checking out the vehicle. The power windows and a/c are now working as well.
I originally thought that someone had connected the battery or jumper cables and blew the fuse. Now after seeing the amperage out put of the alternator and the rating on the factory fuse, I think the fuse blew by design or accident to protect the alternator from being damaged by an excessively low battery condition. The fuse is supposed to be rated at 140 amps. There are two options for the alternator on this truck. One is a 100 amp unit and the other is a 130 amp unit. In theory the 130 amp alternator operating at full output for and extended period of time could melt the fuse material. In a close up look at the damaged fuse it looks melted. It does not have the flash marks on the clear plastic indicating a blown fuse caused by a strong short. at this point it is just my opinion but I would be interested if others have this same condition and can confirm nothing was connected backwards.