Turn signal/brake light glitches

[Broke]

First post so hey, nice to be here, but I've recently acquired a '89 MJ that has been giving me a bit of trouble. The turn signals began flashing slowly under normal operation, then when the brake is applied they go solid. All four lights are working, tested with the hazards (which the button for is not present so that was 'fun') and they worked. The left seems to be functioning semi-normally, but the right is giving real issues. If the truck is off, with the key out, pressing the brake turns the brake lights on as normal. If I swing the blinker lever to the right, and THEN depress the brake, the blinker dash light comes on solid, and so does the radio and other electronics. I've replaced both the flasher unit (bottom one on the fuse panel, was that right?) and the right rear brake bulb, and the symptoms continued but the flashers worked at the normal rate under all conditions thanks to the new electronic flasher. The truck is actually sitting at work waiting for one of the techs to do the differential rebuild so I don't have it with me, but I'm gonna try replacing the left bulb too since I have it anyway, and double check the sockets of both when I get back to it tomorrow. Grounds have not been refreshed yet.

 

It did spew coolant from the bottle before this happened so I dunno if that screwed with anything.

[gogmorgo]

Coolant spill shouldn't affect your lights

First thing to check is make sure you've got a good ground. The taillight harness ground is the hex screw behind the driver's side tail light. I wanna say it's an 8mm but don't quote me on that.

Second thing to check is to make sure that there's a proper double-filament bulb (either 1157 or 2057) in both the upper and middle taillight sockets. One filament on each is for your tail lights and the other filament on one bulb (can't remember which) is your brake/hazard and the other filament on the other bulb is your turn signal. Also check the front turn signal/parking lamp bulbs.

One other thing to check is the condition of your headlight switch and wiring. I'm guessing they're a little melty, which while probably unrelated is still something you should address before it becomes a huge (and I mean set-your-truck-on-fire huge) problem. It's best to upgrade to a relay headlight harness.

The old style flashers rely on the load going through them to determine blink speed, which is why they always blink faster when a bulb's out. Blinking slowly means there's a much bigger load, either a short or corroded wires/connections somewhere. An electronic flasher isn't affected by the load, which is why yours "fixed" the blink speed problem... but it only addressed a symptom. You've probably still got some super dim lights somewhere.

One other common problem is if you've had trailer wiring added. Trailer lights were not a factory option and usually they were crudely hacked in, which can cause problems. Also just general taillight harness issues. Yesterday I replaced my entire harness with one from a wrecking yard because it was falling apart (trailer wires crudely added then removed! in addition to rodent damage) and it was beyond salvage.

[Broke]

Okay, I'll grab another pair of bulbs and replace all four just to be sure, and do the grounds while I'm in there. The guy I bought it from said it needed a new headlight switch, which came with it and is sitting in the cabin atop the also included new speedo cable, but I decided it must not after trying it and everything worked properly. The backlight to the dash is pretty dim though. I'll go ahead and swap it in, then see where that leaves me.

[gogmorgo]

I'm sure you already know it, but the dash lights can be dimmed and, uh, brightened, by turning the headlight knob. The rheostats get old and flickery, so that could be why it needs replaced. Take a good look at the connector while you're in there for meltiness.

[ParadiseMJ]

Look at your tail and blinker sockets themselves and make sure they're not crusty, corroded.  take each bulb out and look inside, clean (or replace)as necessary. 

 

X2 on looking at the headlight switch...it's a common failing part.  The dimming dash points to the rheostat...it's just a big long spring, sprung out. The headlight switch isn't just for the headlights, it's a junction for running, blinks, dash, etc.

 

Solid blinker indicators are a sign that you have a funked up socket or a blown bulb(s)

[Megadan]

From what I know with my 88, the Turn signal and reverse lights are on one circuit of the fuse block while the hazard and brake lights are on the other.  I had a lot of quirky issues like you are having and I ended up replacing almost every fuse in the block as well as cleaning out some corrosion.  Half of them had the plastic falling off the blades, 3 were so loose the fuse would barely stay in and I had to use a pick to pry the slots in a bit (battery disconnected lol).  Going over all of your chassis grounds is worth doing as well.

[Broke]

Well I managed to get back at it yesterday, all the lights were intact and I cleaned out the sockets. Symptoms are actually a bit more than I knew, the right signal is lighting all four bulbs when blinking. The left signal does not. My suspicions currently lie in the aftermarket tow hitch hookup dangling from the harness. Any other tips?

[cruiser54]

The hitch wiring. 

[gogmorgo]

The trailer wiring is not a bad place to start, especially if the connection point is wrapped in old nasty electrical tape and the wiring around the sockets and other connections is in decent shape.

If all four bulbs are blinking, you've got power to the tail light circuit. Beyond the sockets themselves in the back, the other point where the taillight and turn signal lights come together is at the front turn signal/parking light (the rectangular one below the headlight), which should also have a 2057 bulb in them. Are any of the lights on the front of the truck coming on as well? If not then the issue is most likely isolated to the taillight harness. Another way to check would be to see if you've got power at the connector wire to the tail lights when the turn signal is activated. I believe the tail light wire on your '89 is a blue wire.

 

The super slow blink speed you were noticing before is definitely down to having all the tail lights blinking. If you still have the old flasher it's probably still good if you want to keep it as a spare for once you've sorted out the problem.

[Broke]

Fronts are working 100%. EL12 has them blinking full speed, swapping the old metal flasher from the hazards gives them about 90-95% speed blinking to the left. Everything put together is telling me that, as the harness runs down the left side of the frame, the short is almost guaranteed to be in the rear tail harness between the lights. It's has an aftermarket bumper too, but the wiring looks original to the harness. Everyone else at the shop seems to think it's the tow hookup as well. I'll keep you guys posted once I get back to it and pull the wires out.

 

I will say that it's definitely more beat up than I thought it was once I started pulling panels apart. Not to mention the old coot I bought it from left his grass in the steering wheel and left the screws off the back of the cover. East Texas hicks are a funny bunch.

[HOrnbrod]

Have you checked the rear harness ground? It's behind the left tail lamp. Pull it off and make sure the ground connection is clean and solid.

[Broke]

It was in fine shape, took less than two minutes to check. The grounds I've looked at so far seem to be fairly intact and in good contact but I've cleaned them up as I've gone along regardless. I still have the engine bay to do, but I'll likely get around to that when I pull the dash itself to do the headlight switch, speedo cable, and reconnect the AC vac line to the control box.

[cruiser54]

Tips 1,3,4, and 5 when you get a chance. 

 

18 and 29 also, as 29 improves the rear lighting ground also. 

[Broke]

Hey gogmorgo, I saw in another thread you mentioned a JY taillight harness. What does swapping that entail, if I decide to just replace the whole thing and be done with it rather than trying to traverse the PO's (or even worse, PO to the PO) crappy trailer splice? Are there any harnesses that just drop in? I might be interested in swapping out the existing lights anyway because they're subject to the same 'half the screws are missing, all are different, and some of the holes are stripped out to begin with' problem the rest of the truck seems to have.

[gogmorgo]

I pulled it from another MJ, so yes it just dropped in. I don't think there is another that would work in modified. Sorry I can't be much more helpful than that. As far as the light assemblies themselves, the only ones that will fit unmodified are the MJ tails.

Completely removing just the one splice shouldn't be too monumental a task. You might need to add a small section of wire in the middle depending on how butchered things got, but really it's just matching and splicing maybe five wires together.

In my case the rodent damage was a bigger problem than the hacked-up trailer wiring, and I kinda lucked out finding that harness. There wasn't enough of the corroded wire left at a couple sockets on mine and I was really only trying to find the components. There's a great yard nearby that has a few fairly complete MJ's that haven't really been touched much in the last few years, so I knew I'd be able to find at least something.

[mrmel2you]

Surprised nobody mentioned this----I have a '90 MJ and had basically the same problem, turned out to be the connector to the brake light switch.  Unplugged it, cleaned the connector tabs put in a new brake light switch, used a little dab of dielectric grease and plugged it back together----problem solved :)  

[Broke]

Well $#!&.

 

http://i.imgur.com/Ic4EOPK.jpg

Doesn't look like there's any $#!&ty splicework for me to undo, it's all attached via penetrating clamp almost at the connector itself. Everything looks damn near stock. I did forget to check the brake pedal switch, which is the next item on my list and I'll be able to look at it tomorrow when I clock out and pull the dash bezel to do the underdash work. The other techs suggested that the radio could be wired incorrectly which while probably irrelevant, is also probably true.

[gogmorgo]

I would also hold little faith in any wiring done by someone who would use marettes,,,

 

If removing that disaster doesn't fix it, there are also other points in the harness that could be going bad. I had some cracked insulation (simply from being old) at the sockets.

[HOrnbrod]

Undo the $#!&ty splicework/hack job of the three wires that are tapped into the harness and go to the wire nuts. That's not factory and is probably the cause of your problem.

 

Crap - Gog beat me...............

[Broke]

Yeah, it just hit me that I should have simply unhooked those things while I was there, and snip the one that's taped and checked to see if that did anything. That'll probably solve the issue altogether. I'll do exactly that when I get back to it tomorrow, and just make an afternoon of doing everything I possibly can. I'll bring my laptop along so I can just run through as many of Cruiser's tips as I can in one sitting. The PO (maybe PO to PO? Was told the one before him tried to restore it and gave up) has absolutely awful wiring skills. I'll be making more threads about this truck's wires for sure in the future. Fun thing I learned from the lead tech today when demonstrating the symptoms, the AC compressor clutch is grounded to itself, locked open, with a little loop of wire. I think that's what he meant by "it works, but I broke the cable on accident" and not the control cable or vacuum tube in the dash like I had assumed he meant. This thing is like a kinder egg of disappointment. At least it runs.

[Broke]

Sick saturday so I didnt get to work on it. Ran a quick check on my way out the door today. Disconnected the entire tail harness, flipped to the right, hit the brake, and the right indicator came right back on again. Any more points where they could cross?

[cruiser54]

Look at the ten pin connector in the link below:

 

http://cruiser54.com/?p=35

[Broke]

New turn signal switch has eliminated the problem.

[cruiser54]

thanks for reporting back. 

[Broke]

Planned on it, had the switch for a while after a new old-timer took one look at me fiddling with the truck for three seconds and told me it was the switch. Hadn't had the chance to throw it in until today.