Hi all. I've been struggling with a problem on my 99 silverado for some time now. I've done a lot of searching on-line, but have not been able to find much help... the symptoms I'm having don't seem too common or I'm not coming up with the right search terms. I'm hoping someone here might have some suggestions. Here is what I'm seeing:

• Turn signals alone work fine.
• Apply either L or R turn signal + brakes: Turn signals(both sides) flash. Brake lights(including center) flash. License lamps flash. Front signals(both sides) flash as well.
• Apply either turn signal + parking lamps: same as applying brakes.
• Apply brakes only: brake lights come on, but turn signal lamps (front and back, both sides) light up (steady, but dim) as well. The turn indicators on the dash also light up.
• Head lamps work fine.
• Reverse lamps work fine.

I've had this problem for some time, but it was intermittent initially which made it very difficult to troubleshoot. Now it seems to be pretty much constant.

I've pulled every bulb out at every corner one at a time - none of them affected the problem.

I've requested the service manual from my local library so I can look at the wiring diagram. In the meantime I was hoping someone out there has seen something similar. Does this sound like a bad ground connection? Shorted socket? A problem with the multifunction switch?

Any suggestions would be appreciated. Thanks!

 

A bad ground could cause that.

 

Thanks! I agree, and that is where my thought process keeps taking me. The only thing I can't understand is if it were a bad ground, why would the turn signals work ok by themselves? I haven't been able to find the ground locations yet, but once I get the manuals from the library, they should tell me. Thanks again. I'll report back once I learn something.

 

Something tells me it may have problems with the brake light switch. Just a thought.

 

I hadn't considered the brake light switch. I'll look into that as well. Thanks!

 

You may check the bulbs also, I have seen bulbs where the filament broke and grounded to the casing of the bulb.

Nevermiind, I reread your post and seen where you checked all the bulbs.

 

Still working on this one. I replaced the rear tail light junction block under the rear of the truck. Someone one with similar symptoms said it was the source of their problem. Unfortunately it wasn't the cause of my problem. Oh well... it was pretty cheap and easy to swap. Today I pulled all the fuses for the exterior lights, one at a time. I won't go into all the details, but based on what I saw, I'm becoming convinced I have a bad ground at the rear of the truck. If anyone one knows where the ground connection is for the rear tail lights, that info would help me out. The wiring diagram from the manual I have doesn't give that much detail. Thanks.

 

hello patrick 100, i am having the exact same problem as you with the same truck. if you solved your problem i would greatly appreciate e reply as i have tried many things and have had no luck. thankyou michael l.

 

Yes I have afriend with GMC truck with the same problem also.

 

hi timberwolf, i have been working on this problem for the past three weeks.my truck won't pass inspection so i have to solve it. i first checked all the bulbs and sockets. then i removed the multifunction switch and disassembled the switch and cleaned and very lightly regreased it . then someone online had the same problem and they said that a frayed wire to one of the rear lights was shorting out.i removed all of the wires from the plastic split tubing it was in and inspected it, and also removed the ground wire from the bracket that holds the spare tire ,cleaned it all up and reconnected it.also checked all of the rear light sockets that plug into the rear lamps junction block,and replaced the brake light switch. i removed the fuse box in the engine compartment and under the left side of the dash and checked the wires there replaced the turn signal flasher and the parking lamp relay.i was going to replace the junction block that the light sockets plug into but patrick100 said he did that and it didn't help.tomorrow i'm going to start checking the sockets and junction bock with a multimeter but at this point i sure wish there was someone out there that has solved this problem. thanks,mike