Wiring Gremlins

[Megadan]

Yea.  So my reverse lights don't work, and now the brake lights decided to stop working as well.  The interior lights also don't entirely work, but I have that part somewhat figured out.

The reverse switch on the trans is new, as is the wiring from it to the harness, so I know that isn't the issue.  I have checked the fuses that I can check and aside from one, the rest look fine.  The problem is, I have no way to identify which fuse goes to what.  

So that being said, if there is a link or if anybody has available, a chassis wiring diagram from the lighting on these trucks it would be a huge help.  Or if anybody can think of a common problem area that may be the cause of my own headache, please let me know.

Thanks for the help so far guys!

 

[cruiser54]

Check the "trans" fuse. 

[Megadan]

Got it!  That was the culprit for my reverse lights, thanks cruiser!  The fuse diagram I have listed a different slot for the back up lights.  I crossed that little part out on my diagram lol

The fuse was also the culprit for my brake lights (I had a hunch when I realized my hazards didn't work either).  The fuse itself tested fine on my little tester tool, but I replaced both anyway.  I also noticed that all of the fuse terminals were dirty/corroded and a bit loose, so I hit them with contact cleaner and used a small screwdriver to pinch them together.  Now all is well.

[Megadan]

Ok, so since this truck is ripe with electrical pains in my butt.  It has intermittent wipers, and they operate on one speed no matter the position (slow) so I am thinking the module is the problem.  I am going to try and get up under there and bypass it to see if it makes a difference.  However, that leads me to another question.   Does the windshield washer fluid circuit go through said module as well, or am I looking at replacing the switch itself.  The pump is new and verified as operational via. jumping it off the battery.

Also,a couple of my gauges aren't reading right.  Specifically, Voltage reads way low (tested at 13.8V running) at 10-11V.  Gas level reads about 1/4 tank low, and I inspected the sending unit when I replaced the fuel pump and it was in excellent shape with no corrosion.  I am assuming the fuel gauge is a resistance issue, which wouldn't surprise me given the amount of corroded wire I have found in this truck so far.  Is there a voltage or resistance range I can test for with the Sending unit to the gauge cluster?  Any ideas on what to look for with the voltage gauge?  

[cruiser54]

Try this"

 

Improving the Instrument Panel Ground

 

The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without wearing a hat, you will see a black wire attached to a shiny piece of metal almost directly above the hood release knob. The screw will have either a ¼” or 5/16” head on it.

 

This ground point is responsible for handling the ground circuit for the following items: Dome lamps, Seatbelt and key warning, trans comfort switch, wiper switch, headlamp switch and delay module, fog lamp switch, cargo lamp switch, all instrument panel grounds and illumination, power windows and door locks, cruise control dump valve, and a few more things.

 

The problem is that where the ground point is located does not have a good contact with the chassis where the ground should be. The solution is simple.

 

Make up a jumper wire with #10 gauge wire about 10” long. On one end, crimp on a ¼” round wire terminal. On the other end, crimp on a 3/8” round wire terminal.

 

Remove the screw from the existing ground wire and attach the small terminal of your jumper so that the original wire and your new jumper share the same attaching point, one over the other.

 

Look above the driver’s side plastic kick panel just forward of the top of the hood release knob. You will see an 8mm stud there. Attach the large terminal end there with a washer and nut over it tightened securely. 

 

**Special note for Comanche owners: Make your jumper wire 12” long and attach it on the driver’s side kick panel close to the fusebox on the 8mm stud.**

 

 

Revised 11-29-2011

[Dillithium]

I have the same problem with my reverse lights and the fuel gauge, I haven't started with the fuel gauge yet but I'm pretty sure I can tackle that.

 

With the reverse lights I've already replaced both lights, cleaned contact points and still nada. So I wanted to try the transfuse, but I don't have one?

 

This is my fuse panel under my dash:

 

 

I still have to test the switch on the transmission itself, but if that doesn't work I'm not sure where to go next.

 

Tomorrow I'm improving the instrument panel ground, too. Just have to go buy an assortment of wire and attachements.

[Megadan]

On mine it was in the very top row, on the left (in your picture).  The actual location itself is not labled, but a 7.5Amp fuse is located there.  This is assuming that there isn't a difference in the fuse block between different year ranges of Comanche, or Renix vs. HO versions.  I have a 1988 Pioneer 4.0L if it matters at all.

 I know that some other guys have said that a connection for the lights behind the drivers rear wheel can also cause problems with the reverse lights.  I haven't had a chance to do the ground improvement for my instrument panel, but I am hoping it makes a difference.  I have a feeling it's not going to fix all of my problems though.

As far as the fuel gauge goes, after doing some reading I came across a thread on a different site that mentioned the fuel pump and sending unit use the same chassis ground behind the tail lights.  This is the one ground I haven't touched yet, so I am going to tackle that when I get a chance and see if it makes a difference.  I know it can't be in the best shape, because even with the new fuel pump I can tell the pump is suffering from a voltage drop just by the noise it makes.

Also. from what I have found, there are two ranges for sending units on Jeeps, but nobody seems to agree on what years they switched around the resistance ratings.  90ohm E to 0Ohm F or vice versa.  I guess I can fill up my tank and check the resistance going into the gauge and see which one it is closer to.

[Dillithium]

I got my reverse lights to work without putting in a fuse, just a lot of contact cleaner and two new bulbs. I cleaned off the ground behind my taillight, but I'm going to scrape the paint away with a wire brush and apply some white grease to help it connect.

 

I'll let you know if and how I fixed my gas gauge, I haven't read the ohm output yet but I know that unplugging the connecter didn't cause it to jump to full or empty.

I'm crossing my fingers for the underdash ground or the taillight ground.