Tai lights & brake lights not working

I'm new to the site, but I have been coming here for help on my 98 Riviera. I noticed yesterday that I have no tail lights not even with the head light switch pulled out and also no brake lights at all, not even the third brake light. Checked fuses and relays and they are all fine. Thinking it might be the turn signal switch but wanted y'all's input. Any help would be appreciated, thank you.

First off, welcome to the site

It definitely sounds like the Turn Signal Switch might be bad....if in fact all the fuses are good. The left and right side lamps are on different circuits, and have separate fuses. The rear lights have 2 things in common...the Turn Signal Switch, and G401 (ground for all rear lights). If you lost the ground somehow, your ALC Compressor would most likely be INOP as well, as it also shares that ground. The ground is located rear of the RH wheel house in the trunk. You'll have to remove the trunk "carpet" to get to it.

As for the 3rd brake light....It should light up no matter what. The power feed for it comes directly from the Stop Lamp Switch (on the brake pedal), and is before the Turn Signal Switch in the schematic. It's possible that the bulbs are burnt out, or something else is wrong with that circuit.
I'd check the bulbs first.

Thank you for the help. I checked the ground and it didn't look broke or shorted. But it's odd not having a third brake light. Is there a tail light assembly fuse? I checked the dashboard fuse box and the box under the hood but no fuses were bad but didn't see a tailight assembly fuse.

Also forgot to mention that I do have a bulb that was blown would that cause the rest to stop working?

No, a bulb won't kill the rest of the circuit, UNLESS somehow the filament broke off and landed at the base inside the bulb causing a short, therefore blowing the fuse. BUT, the LH and RH tail lamps are on separate circuits....

There's a HZRD/STPLMP fuse in the RH rear fuse block under the back seat that you need to check.

Alright I will check that, just new to these cars so figuring out where things are still. Thank you for all your help. Nobody around where I live knows much about them and I can't find parts around either.

jsevans0126 wrote:

Alright I will check that, just new to these cars so figuring out where things are still. Thank you for all your help. Nobody around where I live knows much about them and I can't find parts around either.

No worries. Would a schematic(s) help you at all?

I have never really looked at one so not sure if I would know how to read it. I'm not real good with electrical but I can do normal maintenance. Like I changed my wheel bearings when I bought it myself. But as far as electrical I'm a dummy. Lol

If you have a multimeter and a buddy you can test for voltage at all the wires.

Ok I looked more into it after work and what happened makes sense, all four lights were blown in the back. One had moisture in it cause I have a cracked tail light and it blew all four. I'm guessing the moisture shorted it out and caused them to blow. Thank you to all who gave input, I appreciate it a lot.

I have a somewhat similar issue that just came to my attention today.  My 17 yr old drives the Riv now, and her friends pointed out that the brake lights are not working.  Did some investigating, and found all the turn signals work, the exterior lights all work except the 3rd brake light has quit, which I had replaced just a couple years ago.  The rear lights are all on, none burned out, when I start it up.  Stepping on the brake pedal does not result in brake lights lighting up.  I swapped out the HZRD/STPLMP fuse, and the LH and RH EXT fuses from the side of dash fuse box, and checked the ground in the trunk which is solid.  None of these did anything for the brake lights.  

Any suggestions?  Is it possible the apparently prematurely burned 3rd brake light would cause the brake lights to malfunction?  Is there a fuse I may have missed?  BTW, I had the multiswitch replaced with NOS a couple years ago, so that shouldn't be an issue. Almost forgot, the ABS light has been on for a couple months.

1998 Riv wrote:

I have a somewhat similar issue that just came to my attention today.  My 17 yr old drives the Riv now, and her friends pointed out that the brake lights are not working.  Did some investigating, and found all the turn signals work, the exterior lights all work except the 3rd brake light has quit, which I had replaced just a couple years ago.  The rear lights are all on, none burned out, when I start it up.  Stepping on the brake pedal does not result in brake lights lighting up.  I swapped out the HZRD/STPLMP fuse, and the LH and RH EXT fuses from the side of dash fuse box, and checked the ground in the trunk which is solid.  None of these did anything for the brake lights.  

Any suggestions?  Is it possible the apparently prematurely burned 3rd brake light would cause the brake lights to malfunction?  Is there a fuse I may have missed?  BTW, I had the multiswitch replaced with NOS a couple years ago, so that shouldn't be an issue.  Almost forgot, the ABS light has been on for a couple months.  

Dunno but if you have to replace the 3rd light, might as well start there and see if that fixes it.

What is a NOS that you replaced the multiswitch with? Im searching but not finding answers.

Check the switch at the brake pedal. Might be out of adjustment or defective. Any problems with the cruise control? The brake light switch cancels the cruise.

Yep. It sounds like the Brake Switch took a dump....if all other lights work except brake lights and 3rd brake light, it's more than likely the switch. In a rare case, I suppose Ground G302 could be the cause, but I know for a fact there are other things that share that ground.

Yes, the brake switch is what I suspect is the issue at this point. Will check it out this weekend.

Charlie, NOS = New Old Stock, as in new original OEM parts.

Instrument backlights and Tail Lights and "perimeter" lights are out.

I just replaced all light bulbs in the rear tail light assembly about a month ago.

I start the car: Headlight are on, instrument lights are off.  Curious - I turn the dimmer switch for the instruments and they suddenly come back on.

A couple days later I start the car and the instrument lights are off and remain off.  I suspect the tail lights are out too and see they are indeed not on.  The so-called "perimeter" lights at the corners of the car are off too.

This is apparently a problem other people have had as evidenced here:
https://www.justanswer.com/buick/4vqe0-buick-regal-ls-replaced-fuses-tail-lights.html

I cannot find any blown fuses, but honestly, have not looked exhaustively because that would be too simple and not address the reason the fuse blew in the first place. Fuses blow because of underlying problems.

I'm looking at the FSM right now to try to get to a solution. But I thought someone here might have already seen and solved this problem.  

I had a water leak from the passenger side of the moon roof which had dampened some Items in the glove box.  This has been fixed. But it could be that the electrical junction box near that location has developed corrosion issues.  I intend to examine that first. " Rule No. 1 - Make sure all electrical connections are clean and tight".

I apologize if I should have created a new topic, but I can't figure out how to do that.  Apparently it's "easy" which makes it all the more embarrassing that I don't know how.

Thanks for any help or suggestions.

figure out which fuses blew anyway, to reduce your time requirements for looking at the schematic.

I took a test lamp to the fuse block on the driver's side "A" pillar.  With the car running and the headlights on, I found no voltage to the top 4 fuses on the right hand side of the fuse block.  These included the "perimeter light" and "INT" indicated fuses and a couple others which I don't remember.  These are the same fuses which I examined earlier and found ok. I'm almost certain there should have been +V at those locations.  I did find the test lamp lighted at some of the other locations so  I knew it was working.

The FSM was written by Martians.  It's hard to follow their organizational logic.  I guess everything's easy when you know how to do it.

Mars is an exurb or Pittsburgh, PA and Indeed shows number of tech writer positions open there, see https://www.indeed.com/q-technical-writer-l-Mars,-PA-jobs.html -- so yes it could be that at least some of the writers of GM pubs could be Martians. The FSM is written to facilitate transliteration and to be more or less consistent in tone/depth with the other GM FSMs. Most likely, a lot of content is copied year-to-year and borrowed from earlier GM FSMs. As for the technical writers being Martians... maybe.

Once confirming your fuses are good, I'd next look at the taillight wiring for an accidental pinch and at the sockets for shorts.

By The Way: The Riv has a "floating" ground which made it cheaper to implement certain electrical features and functions such as side markers that act as turn signal repeaters and brake lights that the flasher can blink even though they are on via the brake pedal. This is done, in general, by bleeding 12V to the notionally grounded side of the taillights, thus turning the affected light off. It makes more sense if you look at the associated wiring diagram. It is also why if you replace the brake lights with LEDs, the cruise control will disengage at night if you activate a turn signal, but not during the day if you do that.

BTW did you re-lamp the rear lights using LEDs? That can be an issue. Depending on who made your LEDs in the first place you may need to turn them around in the sockets, and for the bilevel ones (the 3057 replacements) you may need to flip the wires onto the opposite side of the plastic insulator from where they are now in order to get them to work at all. Try removing them each from respective socket, turn each 180 degrees, re-insert and test.

The tail/brake lights, and the marker lights, all have 2 things in common. G401 (which is a ground), and the multi-function switch. Yes, the multi-function switch. That thing is it's own "module" that all the lights (except the headlights) run through.

I can't tell you exactly where G401 is, as GM has removed it from Service Information, so I can't see it. I'm guessing that it's either on the rear panel behind the trunk trim, or somewhere on the trunk floor.

According to my 98 FSM, G401 is "Right of the rear compartment, on the edge of the wheelhouse"

Thanks for tips.  I re-lamped with standard bulbs.  I've also had a chronic trunk leak at the right trunk lid hinge which may be the culprit in all of this if it corroded the G401 ground.

The leak was due to shrunken seam-sealer which I need to do a better job of repairing because it's still leaking a bit.

Edit 11/10/17 to add the following:
Well, I thought I had the problem narrowed down to the Lamp Control Module under and to the left of the steering column.  The (4) fuses of the I/P Fuse box near the driver's side A-Pillar that don't have power are supposed to be fed by a brown wire which comes from it.  The brown wire does show +V but the (4) fuses still do not.  Back to the FSM to find out what I'm not understanding about power distribution of this circuit.

I've homed in on the problem.  Probably a loose splice connection between the output (brown 14 ga wire) coming out of the Lamp Control Module and where that wire attaches to the I/P Fuse Block.

Wiggling the wire harness containing that brown wire causes the connection to complete.  There's some connection that not tight. It's not the brown wire's connection to the Lamp Control Module because I have +12V at the connector (before the brown wire insulation starts)

Now, how do I find that loose connection?  I'm going back to the FSM (Book 2/2) to see if there's a splice somewhere on that brown wire between the Lamp Control Module and the I/P (Instrument Panel) Fuse Block.

It would be nice to have a helper to tell me when the running lights or instrument lights go on/off - then I could just wiggle the wires under the dash and tell pretty quickly what is causing the "open" as it gets flexed or strained. Alas, all my helpers are watching football.  My dogs proclaim ignorance of the procedure, which is a likely story.

brutusk1 wrote:

I've homed in on the problem.  Probably a loose splice connection between the output (brown 14 ga wire) coming out of the Lamp Control Module and where that wire attaches to the I/P Fuse Block.

Wiggling the wire harness containing that brown wire causes the connection to complete.  There's some connection that not tight. It's not the brown wire's connection to the Lamp Control Module because I have +12V at the connector (before the brown wire insulation starts)

Now, how do I find that loose connection?  I'm going back to the FSM (Book 2/2) to see if there's a splice somewhere on that brown wire between the Lamp Control Module and the I/P (Instrument Panel) Fuse Block.

It would be nice to have a helper to tell me when the running lights or instrument lights go on/off - then I could just wiggle the wires under the dash and tell pretty quickly what is causing the "open" as it gets flexed or strained. Alas, all my helpers are watching football.  My dogs proclaim ignorance of the procedure, which is a likely story.

IIRC (Abaddon yell if I'm off base here) GM had a problem (not just this car) with certain copper wires work hardening in the field.  They then break inside the insulation.  Certain wires to the ignition module in the 95-6 Riv and certain wheel sensor wiring in S10, Rendezvous/Aztek/minivans and other models had this IIRC.  If wiggling the wire harness containing the brown wire gets you a make-n-break, just use alligator clips or j-clips (the kind used for clipping to DIP IC and other fine leads) to clip to each end of the problem wire and wiggle the harness to confirm the issue.  Old-line auto parts stores, and/or auto parts stores supporting customers like school bus fleets, will probably have matching wire by the small spool or by the foot.  If you have the terminal kit you can then just replace the ^%&^%#& wire.  If not maybe you can borrow one.  If neither, you can feel the wire with your fingers wile flexing it and find the break inside the insulation.   Then you can decide ho to splice it.   By the way one hint - if the wire can be pulled longitudinally in the wire harness bundle, what you can do is estimate how long it is and add 6" to a foot.  Then cut the wire you're replacing at one end and solder the new wire to it.  Pull the new wire thru the harness using the old one. Once the wire is through, clean up the ends and re-terminate.  Sometimes you can leave some of the old wire on the terminal ends, 1" to 2", and solder the new wire to those pigtails.  The issue is you've still got that dirt-rip copper in there, and when that un-replaced section work hardens it will snap.  The following may or may not work: THIS TERMINAL KITand a crimper, along with THIS KEY KIT.  I think your headache will be the terminals; you may be able to get them from a GM dealer or, again, an old-style auto parts jobber.

I rigged up my test lamp so that I could see it as I jiggled the wire bundle containing the 14 gauge brown wire coming out of the Lamp Control Module which feeds the (4) upper, right hand, fuses of the Instrument Panel (I/P) Fuse box.

It didn't take long to find that it was the female terminal on the brown wire which had a poor connection with the spade terminal on the Lamp Control Module.  I missed this before I think because every time I touched the terminal with the test lamp probe, the pressure would cause the connection to be made giving me an apparent +12v. When I withdrew the probe, the connection would be lost again. That's what made me think it was a fault in the wire itself, or in a splice that I couldn't see that was buried in the wire harness somewhere.

After pulling the connector from the Lamp Control Module, extracting the brown wire female terminal from the connector body and some hairy, on-my-back, under-dash orthopedic surgery on the terminal, I was able to tighten up the terminal and get a solid connection established.

It would have been nice to have had a new terminal to crimp on, but what I've done should last a while. For a brief moment I contemplated "fixing" it by jamming a toothpick into the connector bay to wedge the terminal in place, but then thought better of it.  That would work right up till the point I was driving somewhere at night where I really, really needed my tail lights to keep working - you know the place - hundreds of miles from anywhere, raining, cold, etc... and not another toothpick in sight.

I noticed that the brown wire was unusually warm.  Was that because of the poor connection or is that wire overtaxed and causing the terminal "spring" to weaken over time?  I don't know.

I'll be getting that those kits that you mentioned Alberj so that I'm ready for the next time.

Thanks for the help.