Truck Electrical Woes

[crashz]

2004 GMC Sierra 1500, 4x4, 5.3L, automatic.

Yesterday afternoon my right directional stuck on while my foot was on the brake. I thought it was merely a burnt bulb. However the indicator kept lighting (solid) every time I stepped on the brakes. Once home, I put the directional on for left and then right. The left works fine, the right works but causes the brake lights (including the third brake light!) to flash in sequence. stepping on the brake causes the brake lights to work and lights the right side directional in the back only.

So, I tried to isolate a short that I assumed to be in the right side tail light by unplugging the back harness (next to the spare tire). I unplugged each plug that disconnects the tail lights, and bumper lights, however the right directional would still cause the third brake light to flash.

I then pull the fuses for the trailer hitch directionals, which can sometimes corrode at the hitch and cause problems. This changed nothing. I pulled the actual directional fuses next, and replaced them. All fuses were fine. nothing changed. Flicking the high beams on and off seemed to help, as all of a sudden the directional worked fine with out triggering the brake lights and vice versa.

The 4wd drive switch indicated that its in 4Lo, but when put into Drive, clearly is in 2wd (less torque as 4lo jerks the truck at idle ,even with the brakes applied).

I took the truck for a ride and the directional thing came back, but is inconsistent. This moring, the brakes inconsistently apply the directional, but the directional always applies the brake lights.

A unrelated electrical issue is that I have removed the heater blower resistor to replace it, but I'm awaiting the new part.

Anyone have an idea what I should do next? I'm at a loss on this. I just spent the weekend getting it ready for its yearly inspection and performing general maintenance. Now I have fix this before passing inspection, which is due by the end of this month.

Its been a great truck, but the electrical system has been getting worse for the last few years.

 

[deerefan]

2004 GMC Sierra 1500, 4x4, 5.3L, automatic.

Yesterday afternoon my right directional stuck on while my foot was on the brake. I thought it was merely a burnt bulb. However the indicator kept lighting (solid) every time I stepped on the brakes. Once home, I put the directional on for left and then right. The left works fine, the right works but causes the brake lights (including the third brake light!) to flash in sequence. stepping on the brake causes the brake lights to work and lights the right side directional in the back only.

So, I tried to isolate a short that I assumed to be in the right side tail light by unplugging the back harness (next to the spare tire). I unplugged each plug that disconnects the tail lights, and bumper lights, however the right directional would still cause the third brake light to flash.

I then pull the fuses for the trailer hitch directionals, which can sometimes corrode at the hitch and cause problems. This changed nothing. I pulled the actual directional fuses next, and replaced them. All fuses were fine. nothing changed. Flicking the high beams on and off seemed to help, as all of a sudden the directional worked fine with out triggering the brake lights and vice versa.

The 4wd drive switch indicated that its in 4Lo, but when put into Drive, clearly is in 2wd (less torque as 4lo jerks the truck at idle ,even with the brakes applied).

I took the truck for a ride and the directional thing came back, but is inconsistent. This moring, the brakes inconsistently apply the directional, but the directional always applies the brake lights.

A unrelated electrical issue is that I have removed the heater blower resistor to replace it, but I'm awaiting the new part.

Anyone have an idea what I should do next? I'm at a loss on this. I just spent the weekend getting it ready for its yearly inspection and performing general maintenance. Now I have fix this before passing inspection, which is due by the end of this month.

Its been a great truck, but the electrical system has been getting worse for the last few years.

You may think this is crazy, but do you have any problems with mice? They chewed some wiring in an old chevelle i am in the process of restoring and i had all types of lights and signals crossed. It sounds like a wiring problem.

 

[deerefan]

Also, check your main fuse box for corrosion or moisture. Moisture could be causing a short circuit or allowing juice to flow across circuits.

 

[tcartwri]

Also, check your main fuse box for corrosion or moisture. Moisture could be causing a short circuit or allowing juice to flow across circuits.

My old honda did this to me.. Spent an entire weekend looking for shorted wires, when in fact the printed circuits in the fuse block were one corroded mass of green goo.

 

[dodge man]

I had a problem like that on an older car, and it was a problem with a wire in the steering column. It took a lot of work to find the problem.

 

[jeffsw6]

The 4wd drive switch indicated that its in 4Lo, but when put into Drive, clearly is in 2wd (less torque as 4lo jerks the truck at idle ,even with the brakes applied).

This might be unrelated to the turn signal issue. Call your dealer service dept and ask them to look for related TSBs on the transfer case. I wouldn't rush out to do the part swap if they say it applies to your vehicle, but if it is not an electrical problem with the dash indicators/controls, you will need a few hundred bucks fix that your dealer service dept will be very familiar with. :/

As to the turn signals and such, there should be a ~$20 relay that you don't have to take the whole dash apart to replace. I would do that before fooling with anything else, just in case it is simple. This probably will not fix it but taking apart the steering column is a PITA and once you start throwing parts at that you will be into much more expensive parts

 

[Diamondpilot]

I had similar issues in a brand new 05 Dmax. It was in the steering column and in the fuse box under the hood.

Chris

 

[crashz]

Thanks guys.

The electrical gremlins are creeping up on me now and I'm trying to negotiate a new vehicle.

 

[jeffsw6]

That is why I traded my 99. Once I started throwing parts at electrical problems it quickly began to be more headache than the price of a newer truck. :/

 

[crankshaft21]

May not apply to newer trucks, I had a 81 ford and the lights went crazy like yours and it turned out to be the ground wire. It had nearly lost its ground. I took it loose and sanded a good spot and reattached , problem solved. May be your ground wire.