This is just a quick thread to see if someone can see an obvious problem to pursue for my truck’s taillight problems. It started with the taillights on both side going out with brake application and only the right side brake light illuminating. It now has the right brake light illuminated all the time with nothing else working. Now that sounds like a progressive short caused by wire abrasion of the harness somewhere under the rear of the truck (It’s a 1991 Nissan basic 6cylinder p/u.)
But I thought I’d pick the board’s collective knowledge to see if I was missing something easy and obvious before I get all dirty and such. I don’t think the turn indicator relay can be involved since it’s so far upstream but you never know. Anyway, any ideas are welcome are welcome till I get the electrical tape and multimeter out and go digging. Thanks in advance, you mighty gurus, you.
…the taillights on both side going out with brake application…
Sounds like poor/open ground for taillights.
…only the right side brake light illuminating.
Sounds like left brake light bulb out, or possibly broken wire (open).
It now has the right brake light illuminated all the time…
You do mean ALL the time? Brake light switch staying on – could be faulty switch or broken “button” on brake pedal that contacts the swith.
…with nothing else working.
Like you said above, taillights don’t work when brake lights are on, and now the brake lights are stuck on.
Now that sounds like a progressive short…
Brake light always on could be a short, but much more likely is related to the switch. Unless taillight fuse is blown (possible but very unlikely given all the info related), taillight circuit has an open, not a short.
…caused by wire abrasion of the harness somewhere under the rear of the truck.
Certainly one possibility, but certainly not the only one. I’d start by looking at the taillight sockets, after fixing the brake lights.
On reflection, with both taillights (and I’d bet the license lights) out, it wouldn’t be the sockets. Probably a ground wire for the taillight circuit has broken somewhere. Might be easier to install a new ground than to find the break.
I had something VERY similar with a '99 Lumina. It was a ‘going-out but not totally broken’ turn-signal unit thingy (sorry, forget actual name of thingy). One of the tail/brake lights was off intermittently and it took replacing bulbs, bake-pedal relay, etc until we got to the turn-signal stalk thingy. Days would go by without it acting up, then weird symptoms for awhile then work again all of a sudden (twice right after replacing something that wasn’t the actual issue, dang it!). Bumping against turn-signal lever probably made act OK until internal pieces stopped functioning again at some point. Maddening, for sure.
Easy fix but I had never even thought it would be there. Slightly different than OP, but…shrug. Good luck!
Hey! Progress! I realized on disassembly that the left tail light, along with with the right brake light, were both lit with the ignition off. I would think this points to the brake pedal stop switch, does it not? After all, pressing the brake pedal will send current that way even with the ignition off. It looks like it’s time to get my reading glasses on, the ground cable off, and a continuity tester out before NAPA closes, unless I’m missing something obvious (which I do regularly.)
This doesn’t tell enough to be helpful. Is it truly the left taillight, rather than the left brake light being dim? Is there also power to the right taillight? Are the taillights turned on? Do any lights change when the ignition is turned on?
Not sure what you mean by “this.” Have we not already established that the right brake light is always on? If that’s the case, the cause is almost certainly* to be found at the brake light switch – either the switch is faulty or the switch is not being turned off due to the little nub at the top of the brake pedal being broken or gone. This type of problem can get confusingly complicated when there is more than one fault present, so isolate them and fix them as you go to avoid getting mixed up. Find and fix the brake light problem**, or at least disable the brake lights by disconnecting the brake light switch or pulling its fuse.
Once the brake lights are out of the picture, proceed with the taillights.
Both the taillights and the brake lights have power with the ignition off.
Ground cable off? Why?
*99+% likely. It is possible there’s a wiring short to power keeping the brake lights on, but that’s exceedingly rare.
**Including eventually getting the left one working.
Actually, I have to thank you Gary. It was your clue about the stop light switch that sent me in the right direction in the first place. I’m a big enough geek that I’ll still stick my head under the back of the truck to look at the harnesses, all of which were encased in that corrugated shielding. It’s no lack of faith in your advice, which is legendary, but rather my stubborn curiosity.
As for the ground cable off I’m a big chicken when it comes to electrical systems and unplugging connectors, like the one for the stop light switch. I once brushed a wrench across battery terminals in my youth and did some impromptu arc welding. It’s just an old habit with me.
So I got under the pedals and jammed a screwdriver to make sure the plunger on the switch was fully depressed: lights went out like a charm. So I went under the pedals to readjust the switch. I have the switch turned all of the way inward only to find that Nissan has a hole in the brake pedal arm RIGHT where the plunger would make contact. I look around on the floorboards and sure as shit there’s a little circular piece of white plastic with some adhesive residue that would just cover this hole. So I epoxied back on and all is well. why the Nissan engineers went that way I haven’t an idea.
Oh. As for the asymmetry between right/brake left/tail lights? With all my monkeying around pulling the assemblies off and on, checking bulbs, remounting, ad nauseam I managed to work one of the nylon cable connectors boxes halfway loose. I should know better. I used to be an IT guy and the first thing you always check is the cabling.
Anyway Gary, a million thanks. You’re a genuine blessing to this board. If you’re ever in SouCal and want dinner or a trip to Disneyland you got it. Thanks.
