1999 Silverado Exterior light problem... Help?
 

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.

exterior lights malfunction,
 

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.

turn signal malfunction
 

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

exterior lights malfunction,
 

hello everyone, i think i solved my problem with the turn signal lights. i removed the rear lamps junction and tesred it with a continuinity tester and found a ground terminal shorting to the left and right parking lights.i ordered a new junction block online and will install it next week.patrick100 tried this and it didn't work but he may have wires that run along the frame from the front to rear that go to he lights frayed or broken somewhere. i will repost after i install the block. thankyou,michael

Hi Michael,

Sorry I haven't responded to your posts sooner... I've been away from my computer the last 3 days. Based on what you found with the multimeter, I would agree that the junction block is probably your problem.

The good news on my end is that I finally have working lights! My problem was the ground wire that attaches to the frame above the spare tire. The wire was broke just before the connecting ring... probably had too much tension when it was originally torqued down. It took me longer to solve this than it should have because I didn't realize the ground for the rear lights split off and went above the spare tire.

I think I've learned more than I wanted to know about these lights. My advice... if you are seeing similar symptoms, check your ground. An easy way to do this is to create a temporary ground connection and see if it fixes the problem. I did this by connecting a jumper from the ground line of any rear lamp socket (the ground wires all tie together at the junction block) and any bare metal on the frame (I found a spot on the tailgate latch). As soon as I did this, working lights. At that point, it was just a matter of finding where the ground was lost. Seems like the junction block and the connection to the frame above the spare tire are two likely places.

Hope this helps.

malfunctioning turnsignals
 

hello everyone, i finally fixed the light problem. it seems everyone i,ve talked to about this problem had a bad ground wire ,but they were broken or frayed in different places. one guy had a bad junction block but that was not my problem.the groond wire inside the blue connector at the junction block was sheared off inside the terminal. there are 8 wires at this terminal that go to all the rear lights.i should have solved this much sooner but misled myself thinking it was the same problem as everyone else but at least it's fixed. thankyou for all oof your help.mike

Thats great man!