Mechanics

BRAKE/STOP AND TURN BLOTH BLOW

2002 GMC Safari

Electrical problem
2002 GMC Safari 6 cyl All Wheel Drive Automatic 191000 miles

Hi,

I have a 2002 GMC Safari van. My wife went outside to try to start but it would not start. She tried a little while later and still would not start. I tried a few hours later and she said she pushes down on the gas to start so I thought that was the issue since it is electronic fuel injection.

When I started it up the turn signals would not work and I found that fuses 1 and 16 were both blown. I researched the issue and thought it was the multi-function switch so I bought a new one off of eBay from a reputable guy who had old dealer stock. It looked brand new. I installed after a very difficult process and when I pressed on the brake pedal it blew the fuse again. Putting the turn signals on also blows the other #16 fuse after blinking on and off for 3-4 iterations.

I removed all the dual filament bulbs and the top brake light and pressed on the brake pedal and that also caused the #1 fuse to blow.

I removed the brake signal switch and opened it up gently and made sure the front two contacts would be coming open prior to the last contact touching. Everything looked good in there.

The van does have a connection for trailer lights and brake controller. I reviewed those and they are all clean.

I removed the top brake light and everything looks clean there too. The resistors all look good.

I opened the sliding door just in case something was shorted in in there as well but that had no effect.

Any suggestions on how to test the actual connector sockets into which the bulbs reside?

I really thought it would be the multi-function switch but that was not it. Please ask anyone you know who may be able to help on this one as have a $4,000 boat anchor right now.

THANKS!
Avatar
Lind777
June 14, 2010.



Hi lind777. Welcome to the forum. Sounds like you covered the common things already. Don't overlook the electronic flasher if your truck has one. A simple trick to finding shorts is to replace the blown fuse(s) with a light bulb. A 12 volt brake light works well. Replace the fuse with a pair of spade terminals that you can connect a pair of wires to and to the bulb. I use a tail light harness that's soldered to the top of a blown fuse so I can plug it in quickly.

When the short is in the circuit, the bulb will be full brightness and its resistance will limit current to a safe level. You can unplug things and move wires around to see what makes the short go away. When it does, the bulb will become dim or go out.

Caradiodoc

Caradiodoc
Jun 15, 2010.
Thanks. I had removed the turn signal flasher and brake problem persisted. The schematic shows a turn signal/hazard flasher module. Would there be another?

Tiny
Lind777
Jun 15, 2010.
If it has two terminals, there is another flasher, but if it has a whole bunch of them, it is an electronic flasher. You might see a pair of relays inside too.

I'm going to guess your truck uses the older common sense circuit where the brake light is the turn signal bulb too. That would lead the search to those circuits since both systems are blowing their fuses. If you have the newer circuit where the turn signal and brake light bulbs are different, there will be an adapter harness that allows use of a single bulb on the trailer for both functions without shorting one circuit to the other one. There could be a problem with that adapter harness. Most of those that I've seen are plugged in. If you can find that plug, disconnect it to see if that eleiminates the short. It doesn't seem logical that there could be a problem with the wiring to the lights because what are the chances both sides have a problem at the same time? A shorted wire to one brake / signal bulb could cause your problem, but it would only blow the fuse when you use the turn signal in one direction. The other direction should work fine.

Sorry for the delay in replying. My Verizon e-mail system keeps going down, often for a day at a time. Without e-mail, I can't get the automated messages that direct me to your last reply.

Caradiodoc

Caradiodoc
Jun 16, 2010.
Thanks for your help. It turns out that my battery was causing the issue so I tore the whole car apart for nothing. Ugh! I pulled the old one out and used jumper cables from another battery that I have and the flashers started working correctly, etc. I took it up to Advance and it showed that it was only providing 445 cranks for a battery rated at 800. It is amazing how a battery can show 12V and mess everything up.

Tiny
Lind777
Jun 16, 2010.
That is a weird one. I taught four automotive subjects for nine years. Electrical was one of my three specialites and that is something I never would have guessed. Low voltage confuses a lot of computers and makes them do strange things, but low current capacity? That's one to remember. Hope it keeps working. Thanks for the followup information.

Caradiodoc

Caradiodoc
Jun 16, 2010.
Thanks guys. My van's turn signals are also not working. I replaced the turn signal switch, multifunction switch, replaced the signal flasher and checked all the fuses. All the other lights are working well and I just remembered that the battery cables were loose earlier. Maybe it could be the battery as well. I'm going to look into it, thanks for your help.

Tiny
Thunderbolt
Feb 23, 2011.