Auto Parts: Tail light problem on my 1991 GMC 1500, left blinker, wiring harnesses


Question
QUESTION: First my brake lights stopped working, so I checked the switch and it worked fine. They still don't work.  I then had to change my fuel pump by removing the truck bed. When I put it all back together, my rear end lights are all messed up. When the headlights are on, nothing seems to work right.  
-The left blinker actually turns on the dim running lights and will be on for about 3 seconds and then a quick flash and back to on again.
-The right blinker turns on the brake lights and does the same flashing problem as the left, but my license plate light also flashes with both of the brake lights.
-When the headlights are off the blinkers work perfectly, but I have no brake lights or reverse lights.

Any suggestions would be greatly appreciated.

ANSWER: Hi Mickey,

If all of the wiring harnesses for components were re-attached correctly then it sounds to me like you didn't re-attach the body-to-frame ground straps or they are bad. Your ground right now is 'floating' through the other systems in your vehicle (probably the fuel pump harness) trying to get to the frame/battery. This will no doubt put excess stress on other electrical components if not addressed.

Thanks for the question, I hope this information is helpful to you.
Kb

---------- FOLLOW-UP ----------

QUESTION: That sounds like it might work. Do you happen to know where the ground locations are at usually?  I know there is one by the fuel filler neck (it looked pretty coroded) and I saw one by my towing package. But I don't know if there will be any others that I haven't seen yet.
Thanks again Kb- Mikey

Answer
Hi Mikey,

When in doubt, replace. If the original straps look bad or damaged, cut them off and replace with new pieces. The ground strap can be purchased relatively inexpensively by the foot at almost any auto parts supplier. I would add at least two new pieces.

Make sure your battery ground is attached to the FRAME of the vehicle and NOT to the engine. The engine should be grounded via strap to the firewall or better, the frame right where the battery ground is attached. If your battery ground IS attached to the engine directly, make sure there is a ground strap also connecting the engine to the frame and not JUST the firewall because engine mounts make bad conductors.

Attach two pieces of strap between the rear frame rail on the left of the vehicle to a good cleaned spot on the bed of the truck. I usually pick a spot somewhere near the shocks but out of the way of their travel. Use a good self-tapping bolt or a bolt and nut combination if you have the access and space. Do the same thing on the right side of the frame to a good spot on the bed.

Thanks again for the question, I hope this information is helpful to you.
Kb