GM Truck Club Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
163 Posts
Discussion Starter #1
97 C1500 ex. cab, 5.7, auto, 2WD, Silverado
Last Sunday I noticed a fast flash on my right turn signal. Front right light flashed fast, nothing at rear. Figured it was the board, couldn't mess with it. Left turn signal was normal. I can get to work with left turns only.

I think Wednesday or Thursday morning, left turn signal had fast flash, front light flashed, rear did not. Checked bulbs in both rear lights and they all work.

Left turn signal occasionally has worked properly since I first noticed the fast flash. Right has not. A couple of times I turned it on, I think it flashed at proper speed once or twice, then became fast, but it won't do it when I'm trying to watch for that.

Looked at fuses in the courtesy panel and cleaned off prongs. No change.

Switched A/C relay in power distribution center (or whatever it's called by GM) for the brake relay, didn't help. A/C works. Well, I didn't double-switch the relays, I only put the A/C relay in for the brake relay. I couldn't read the numbers to know if they are the same.

Taillights have worked on both sides the whole time. Haven't thought to check back-up lights. License plate lights work. Emergency flashers work at normal speed, on the front lights only.

Friday morning (yesterday) got a frantic/mad/warning horn blowing behind me. No brake lights. I don't know for sure if they worked all week. I think I noticed them once, and I never had any screeching tires or horn blowing behind me. Wednesday or Thursday morning on the interstate somebody did run up on me a little bit when I was exiting, which I assumed was a bad driver but was probably my fault for no brake lights.

Just tried a new brake switch this morning (Sat), NAPA brand. No change.

Does anybody have any tips for this no rear turn signal / no brake lights issue, especially the "start at one side, then spread to the other" behavior? Relay going bad maybe? I don't remember exactly, but when I had the '98 years ago I had to change the right rear light board a couple of times for fast flash/no right rear turn signal, and I don't remember if the brake light worked or not.

If I'm able to later today, I'm going to get back into it and see what I can find with the multi-meter. Oh yeah, I cleaned the wiring ground points at the back and the front fender and the core support 1-1/2 years ago when I had the no taillight / blowing fuse #9 problem. I know I did those grounds but I don't remember right now if I did any others. I'm thinking now that I did one under the dash too.
 

·
Registered
Joined
·
163 Posts
Discussion Starter #3
You have a bad ground in or going to the rear of the truck. Could also be the boards in back too. The multi-meter is your best friend for this troubleshooting.
If that is true, a bad ground, that would point to the one at the back end of the framerail on the driver's side as the most likely culprit, right? That's one is easy to get to and I've cleaned it before.

Or is there one that is close to flasher or relay that would be the most likely culprit?

I have at least one brand new left side taillight board left from the '98. I don't know why the right one would go bad, then a few days later, the left one, but not completely out, still work every now and then. If I can find it, I'll throw a left one in, but I'm not holding my breath. The symptoms are screwy.
 

·
Registered
Joined
·
163 Posts
Discussion Starter #4
I'm really looking for a more in-depth answer, somebody who knows why the top bulbs don't work while the lower 2 do. I had searched before I posted this thread and saw one that seemed like it was going to deal with that topic, but then ended. I found several other similar threads, but I've checked what they said fixed their problems.
 

·
Registered
Joined
·
13,447 Posts
Your saying the uppers work and the lowers don't.
Then you say you have no brake lights and no signal lights
So that sounds like all you have in the uppers is the tail light function.

That is probably not correct,
I don't know the config that you have, but I don't think the uppers are only providing tail lights.

Also, check the back ups.

An easy way to do this in the day time is to back up to a window that lets you see the rear of the truck in the mirrors.

Then, check the owners manual to see what light config you have.
Some vehicles will have tail and brake in the uppers and tail and sig in the lowers
Some vehicles will have tail, brake and signal in all 4.

We/you need to know the correct config.

And, as silver said, you need a multi-meter.
 

·
Registered
Joined
·
163 Posts
Discussion Starter #6
Ray, my rear lights have 3 bulbs mounted in a circuit board thingy, top is brake/turn, lower 2 are tail lights and come on when the light switch in turned on. Currently they do come on. Sitting there with the light switch ON, the lights look normal. I didn't think about checking the back up lights yesterday evening. I found my multi-meter.
 

·
Registered
Joined
·
163 Posts
Discussion Starter #7
Driver's side back up light works, passenger side does not. I'll investigate later if I can get to it. Every bulb was OK the other day.
 

·
Registered
Joined
·
163 Posts
Discussion Starter #8 (Edited)
OK, at the Brake Relay in the Fuse & Relay center under the hood, when I press the brake pedal it shows 12-something volts across the relay inputs (either 12.32 or 12.45 I think it was). I haven't found it on a wiring diagram yet, but I figure that would mean that the circuit in the cab is working properly.

Found my test light. Took apart the right rear light assembly. With the right turn on, the test light has fast flash when checking at the wiring connector plug. So I've got power and ground at the plug.

Couldn't find one new left side light circuit board I know I have. Got ticked off and went to O'Reilly's and bought 2 new rear light circuit boards. TYC brand.

Now left turn signal is normal flash speed, right is fast. I didn't think to set up a mirror or otherwise look at the left to see what it was doing. Both back up lights now work. Left side brake light comes on, BUT, is in the wrong place. The bottom light comes on for the brake. No tail lights come on. Didn't think to look at turn signals. I'll get back to it later this afternoon.

EDIT: I was wrong, the tail lights do come on, they are just very dim. Left turn signals look normal front & rear, fast flash at right front and quite dim, nothing at right rear.

NAPA doesn't have circuit boards ("tail lamp connector panel" is the proper name apparently) in stock and can't get them until Tuesday.
 

·
Registered
Joined
·
3 Posts
You might wanna check your ground. I had a similar problem where mine was hyper flashing and one tail light was very dim. I first messed with the wiring (just moved it around) and that fixed it for a while until it did it again. I then checked my ground and it was very dirty and didn’t really have good contact. Cleaned that up and that fixed everything for me. Good luck anyways I know it’s a pain in the butt to have faulty lights.
 

·
Registered
2010 Silverado 1500 LTZ
Joined
·
5 Posts
Don't forget to check side marker bulbs front and rear. If one bulb of any kind is out on right side, you could have fast flash. Same with left side.
 

·
Registered
Joined
·
6 Posts
Sounds like bad ground / bad bulb. Emergency flashers are not current dependent for flash rate, turn signal flashers are.
 

·
Registered
Joined
·
5,578 Posts
Circuit boards man, circuit boards. A test light works better for this than a multi meter because a test light will show flashing. Pull you tail light boards, and chack @ the pig tail. If all works rite there, then its the circuit boards. Like I said, a test light is much better for this as it will flash with the turn signal. Also on these trucks, the turn signal and brake light work off of the same wire at the circuit board. Most of these trucks have standard wiring. Brown is running lights, green is rite turn and brake light, yellow is left turn and brake light, and white, or black is ground.
 

·
Registered
Joined
·
163 Posts
Discussion Starter #13 (Edited)
Yeah Kenny, I don't guess you didn't see it up in post #8 where I used a test light and had fast flash at the right rear pig tail plug.

I replaced both circuit boards with TYC brand from O'Reilly's. I've had bad luck with TYC brand light parts I have gotten from Rock Auto in the past, so after I installed them and still had the issues reported in the bottom of post #8, I assumed at least one of the new boards was bad. That has been my luck with TYC brand, buy two lights and one side is OK and the other is crap.

However, in this case, it was a bulb problem. I re-used the old bulbs and with going in & out a couple of times, one of the wires that wraps around the bottom got pulled loose and folded back up on the other side. Shoddy workmanship 🤪

Found and fixed that and the lights worked right . . . for 2 days. Fast flash on the left side, no left rear turn signal or brake light. Switched the bulbs around and it works now. FYI, I can connect the bulbs to a battery and it will light up both filaments, either one at a time or together. The bulbs are good. I tried scraping off the wires to make better contact. One of the first things I did last week on the old boards was to clean off as much of the waxy old bulb grease as I could when I was first testing the bulbs. I think I need to solvent clean the bulb bases. Oh heck, I bought a bunch from Rock Auto for I think $0.38 each because I was ordering some other stuff too. They will be here tomorrow.

As another pain in the neck, last week when I found out the brake lights at the rear corners weren't working, I checked the 3rd brake light and it wasn't working either. At the time, the cargo lights worked. I switched those bulbs into the 3rd brake light sockets and they worked. A couple of days later, I found some new bulbs I had bought from RockAuto a while back and I put those in. The cargo lights still don't work. The bulbs light up when connected to a battery. I switched back the bulbs that did work last week and they don't work either (in the cargo light sockets).

I think I remember the same thing on the '98 C2500 I had years ago. At some point after buying it used, I noticed the 3rd brake light didn't work. The cargo light did. After that I could get one or the other to work, but not both. I guess that plastic bulb holder/circuit board thingy goes bad too. Or maybe simply the connections need to be cleaned.
 

·
Registered
Joined
·
5,578 Posts
AC Delco does make replacement circuit boards. I also have TYC in my 97. They are holding up good for now. I started with Dorman boards when my OE ones started acting up. If I ever need boards again, I will get AC Delco. I back my truck in, down the driveway, and there is a fence and gate that I park in front of, so in the morning when I fire up for work, its early so I cut on my lights, and look in the rear view, I can see my lights reflecting off of the brick and fence, then I put the truck in drive, I have to step on the brakes, so I can see that they are working or not too. So far so good for me. Keep pluging away at it, youll get there.
 

·
Registered
Joined
·
163 Posts
Discussion Starter #15
Replaced bulb that is good (will light up when connected to battery) which I had put in the back up light socket with a new one that arrived today and it works.

Started to mess with the cargo lights and found that the left side (driver's) was working today, wasn't yesterday. Replaced right side bulb with a new one and it works. Previous one works when connected to a battery.

I guess it is old oxidized connections that all of a sudden started acting up together, must be because of lower voltage / ground going bad. I cleaned the rear light wiring ground on the driver's side frame rail last week, battery was bought last July, so I will clean the other ground points in the next few days.

Oh yeah, I got backed into, a hit & run in a parking lot last weekend. Hit the rear bumper and tailgate. Not horrible damage, but still, it's an all original truck in really good shape.
 

·
Registered
Joined
·
138 Posts
not sure this will help, your tail lights are routed through your headlight switch , my cargo lights wouldn't work till i replaced it,
 
1 - 16 of 16 Posts
Top