I bought a 97 GMC Sierra SWB yesterday. It seems to be a good truck but has a few issues. The previous owner told me the brake lights and the turn signals work sometimes , sometimes they don't. I been piddling with it today a little. I found the 30 amp fuse under the hood had blew. I replaced it but they still don't work. I'm guessing when they decide to work again it will blow that fuse again. I'm wondering if anyone has had this problem before and could point me in the general direction?


Another problem is with the AC. Its fully charged and works perfect if I run a hot wire to the compressor. Turning the switch on the instrument panel isn't putting fire to the ac clutch. The instrument panel itself was replaced new by the previous owner trying to get it fixed.

Any ideas would be greatly appreciated.

 

To find the problem with the lights, you are going to have to get a volt meter and start tracing. Find out where the voltage is lost or where the short is that is blowing the fuse. What was the 30a fuse that blew labeled?
Check to see if the voltage to your compressor is getting through your low pressure switch. You should have a switch that shuts off the compressor if the system pressure is too low. If the ac works, you may have a lp switch keeping the compressor shut down.
Good luck. Let us know what you find.

 

I agree on the A/C - those low pressure switches are known to go bad. You can try jumping a wire between the terminals that plug into it and see if the compressor comes on.

On the taillights I would start by looking at the ground under the rear of the truck. I have come across a few that have either had or still have a trailer harness under them that was hooked up wrong or if someone took the hitch they may have not connected the ground back or it may be loose. Also check the circuit board in the taillights themselves. They are known to corrode.

Good Luck!

 

Fiddle with the hazard switch and see if you can get them to work.......sounds just like mine when the multi function switch went bad

 

Thanks, I got a couple a volt meters and test lights. I'm pretty fair mechanic but I also DESPISE trying to trace down electrical problems.. I will see what I can find out today after work.. you know what I was hoping for, that this would be a common problem and somebody could send me straight to the source....

 

the multi function switch is a common problem....and about a $300 fix

 

I just went out and played with it some. I took my left rear tail light assembly out and unplugged it. I got my test light and I have fire there. My test light flashes with the front blinker. NOW, that means the problem IS in that assembly RIGHT? I'm 99% sure but looking for confirmation....

 

That light socket back there is that a junk yard / Dealership item or can it be bought at a good parts store? I took the other side appart and found the same thing. My test light flashes for the blinker and lights up when I press the brake.

 

They are available at some autoparts stores b/c it is so common. If you have a collision parts house like we have Keystone Automotive here they can be purchased there as well. The last time I was at Autozone they had them there for sale though. If your lenses are in good shape you can buy just the circuit board, but fresh clear lenses always look good and don't really add too much to the price. On rare occasions you can clean the rear of the boards and the inside of the sockets with some electronics cleaner and a Q-Tip. Might be worth a try first. Good luck!

 

They are both fixed. Doorman part# 70001 $ 29.99 for the pair at Autozone.. I replaced just the circuit board. My lenses are fine