86 CJ7 electrical

[SubRMC]

I just bought my first jeep, an 86 CJ7 , on Friday. Amongst the many things to restore, the electrical system needs attention. My first issue is the speedometer lights all remain illuminated all the time. None of the gauges in this component are tracking. Any assistance would be appreciated.

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[Les]

This is a total guess, but could it be that you are getting stray hot battery voltage (+) into the case ground for the gauge, if the lights are staying on and the switch is off and verified to be open circuit? The common case ground is also the only thing I can think of that all the lights (illumination, brake, Transfer Case , etc) have in common, that could cause all of them to illuminate as well as cause the gauges to be on the fritz. If so, it might be something internal to the gauge and can be remedied by simply replacing the speedo. You can check this theory by using a multi-meter that has the negative probe affixed to a good ground, then put the positive probe on the case and see if you are showing any current flow. If you are, it may not be 12 volts, but it would indicate there is a problem.

Of course, this is assuming that it is only one issue that is causing all your problems and not a combination of things, such as loss of continuity between the gauge and the sending units, bad switch, etc..

 

[SubRMC]

I appreciate the reply, Les. I wrote the post from my cell phone in a hurry and it seems I misspoke. The lights turn off as usual with the key removed. With the key on, all of the lights are lit (Transfer Case , high beam indicator, turn signals, back lights, etc.) and the temp gauge, speedo and fuel gauge are all stuck. I will check for the voltage at the case with the key on and see if I get anything that way. I have no issue replacing the unit, but I wanted to be sure that's where the issue was before I spent the money and the time. There are numerous other electrical "issues" I have to address such as the blinkers (and hazards for that matter) and brake lights don't work yet, either. As you said, it is highly likely that all of these are related in some way. Thanks again.

 

[Les]

I appreciate the reply, Les. I wrote the post from my cell phone in a hurry and it seems I misspoke. The lights turn off as usual with the key removed. With the key on, all of the lights are lit (Transfer Case , high beam indicator, turn signals, back lights, etc.) and the temp gauge, speedo and fuel gauge are all stuck. I will check for the voltage at the case with the key on and see if I get anything that way. I have no issue replacing the unit, but I wanted to be sure that's where the issue was before I spent the money and the time. There are numerous other electrical "issues" I have to address such as the blinkers (and hazards for that matter) and brake lights don't work yet, either. As you said, it is highly likely that all of these are related in some way. Thanks again.

I misspoke as well, in the first sentence of my previous post, because I was referring to your headlight switch and not the key switch...my bad.

Yes, it does sound like you have an issue like what I described above. Since power to any part of the gauge only is available when the key switch is on (except back lighting), my original theory is still possibly valid. When you turn the key on, you are powering up basically all the dials in the gauge. All the lights depend on the position of other switches to function, such as the one that turns on your brake light, the one that turns on your Transfer Case light, your headlight switch, etc.. So, if you are getting all the lights at once when the key is turned, you have to be getting stray positive(+) voltage into the common ground. This will not only turn on all your lights, but also send a reverse polarity back through your gauges and cause them to go haywire. I'm guessing that when you turn the key on, you are not only getting the lights, but for an instant your gauge needles will flicker then peg in one direction or another?

I'd pop out the back light sockets when you put your multi-meter on the gauge to check for stray voltage, just to eliminate the possibility that it is coming from your headlight switch. If the gauges and indicator lights start working correctly when you do this, then there is your problem...if not, its a stray voltage coming from someplace else and I suspect there is an internal fault to the gauge. However, in the past, I have seen the stray voltage come from other locations and get into the ground circuit.

Good luck!

 

[SubRMC]

I will give your advice a shot later on today. I'm trying to finish up some work around the house. Last night I unplugged the brake light switch in preparation to work on it today. I just took a break and went outside to look at it and realized one of the two posts on it was not inserted in the connector housing. This is likely the source of the problem with those lights, but it doesn't rule out the switch completely. The red and pink wires going to the brake light switch are also spliced into another connector. It was not connected with I bought it, but I found it's mate under the dash. Perhaps these go to the blinkers? We'll see in a little bit. Any advice on connecting the brake light connector? There doesn't really seem to be any easy way to reach to plug it in.

 

[Les]

Ugh, sounds like you are dealing with similar, previous owner induced electrical issues, like I found when I bought my Jeep. As for getting to everything back there, I finally just gave up on the "laying upside down thing", when I had to get at the brake return spring and loosened my entire instrument panel and slid it back, so I could see and access everything. Your back and neck will thank you.

 

[SubRMC]

I don't know if my back can handle it again. I tried for about a half hour today. I'm thinking, though, that the previous owner might have disconnected the lights because of an electrical short in the speedo cluster as you described. I'll update again when I can get out there with the multimeter.

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[SubRMC]

I had to charge the battery again. There is definitely something drawing on the battery all the time. I turned the key this time, after changing nothing with the Jeep, and there are no lights and the engine wouldn't turn over. I'm tired and out of daylight for today. Thanks for all the help. Time for beer and sleep.

 

[Les]

Yes, it does sound like you have a stray hot (+) getting to ground someplace. Sleep is good.....but beer is better.

Good luck finding the issue tomorrow.

 

[Project86]

When I gave up and removed the dash off my jeep, I found a, maybe a #10 sized, red wire that had melted/morphed into all the surrounding wires. If I remember I get a picture of it. I found an unbastardized wiring harness and made the swap.

Laying upside in an uncomfortable position sucks.

 

[SubRMC]

So I bought a new speedometer last week and just got it hooked up this morning. I double checked every connection to it and verified it against the FSM. I labeled every wire based on where it SHOULD be and not where it was. There was so much wrong that I don't even want to get into it here. Needless to say, it is hooked up correctly now. I even hooked up the new brake light switch.

I started the Jeep and tested the signals and hazards...nothing. No big surprise; I figured there would be more than one thing wrong. I depress the brake pedal and the right turn signal indicator comes on steady. I couldn't see if the actual brake light was coming on as I had nobody to check it for me. The left signal indicator didn't come on, but the bulb could be bad so I can't rule that out.

My question is: do the signal indicators come on when the brakes are applied? It doesn't sound normal to me, but this is my first Jeep. If not then I've got crossed wires somewhere. Any further guidance on pinpointing a short if one exists? I'd really hate to have to replace the entire harness over this.

ETA: The brake lights do come on with the brake applied. Maybe still a rogue (+) causing the signal indicator?

 

[Torxhead]

The turn signals will operate with the brakes on. Here are some schematics for the '86, possibly a printed out version can help you out. The identified color of the wires are there also.

 

[SubRMC]

Thanks for the schematics. I have the Haynes and the printouts from AutoZone. I just dug through the fuse box. The previous owner had put a 25A fuse in the IGN/LPS slot, which is supposed to contain a 3A fuse. It was blown beyond recognition, but I don't know how long ago it blew. I replaced it with a 3A and it blew right away. At least I know the short is somewhere in this part of the system now. The brake light switch wires are spliced to another connector shaped like a "T", but I can't find its mate under the dash anywhere.

Edit: Another drawing says the IGN/LPS slot is supposed to contain a 15A, but I blew one of those, too.