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Weird Wiring Issue

comancheon33

NAXJA Forum User
Location
Casey,Ia
I just picked up an 89 MJ a couple weeks ago that would not start. I found I had no injector pulse. Which lead me to check the stator and the ecm. I grabbed a spare ecm from my shelf and it started and runs great. I still have a few things to work out on it but for 200 bucks it runs so be it.
Anyways here is the problem I got. Everytime I turn the key on to the on position the park lamps light up. At first I figured one of the prior may have wired it that way but cannot find any eveidence of that. So I messed with it for a few hours over the week. I cleaned up grounds, including the ground behind the left taillight and replaced the ground from the battery to the bock. Made a new ground from the battery to the body. After all that was done the bulbs would light up only to a slight orange on the filament. I still need to replace the ground strap from the block to body on the rear of the head. Parts store was out the day I was there. I normally run a short battery cable there just for the overkill aspect and it is fairly cheap.
I know it must be a groung issues but I am about out of ideas on what to do to end this. Do you guys have any ideas on where I should go next? I would like to get this gremlin chased out so I can move ahead and finish the 4wd swap. I already have the dana 30 and 3 inch lift on. Thanks in advance.
 
The usual crossover from the key on circuits and the constant power circuits (like the headlights) is the radio. Various ways to screw up the wiring. It may be a combination of crossed wiring and poor grounds.

Or maybe somebody just tried to wire up daytime running lights.

Pull the tail lamp fuse and see if the lights go out. Turn off the radio and look again. The tail lamp fuse and instrument (dimmer) fuses are after the headlight switch. Radios often have two lighting modes, dimmer and constant, if somebody wired a hot wore into the dimmer wire, it could do what you describe. I guess there are other answers though.
 
There is no radio currently in it. Prior had hacked off the connector and spliced something in there. I have removed all of the wiring conections and checked there already. I beleive it is a backfeed because with the key off and headlights on I can still dim the dash lights with the headlight switch. If the key on I cannot do so. I cannot find any evidence of someone tryin to rig up a wiring to make this happen. Thanks for the help so far.
 
The most logical place for the ignition switch power (either the brown wire or the yellow wire)circuit to get into the parking lamps circuit, is through the instrument light dimmer circuit for the gage cluster and the clock.
Pull the instrument light fuse. See if the park lights go out.
The path for the running/park lights is from a fusible link (always hot) through the 10 amp park/Illumination/clock fuse up to the headlight switch then to the parking lights *and* through the instrument dimmer resistor coil and back down to the instrument illumination fuse and back up to the gage cluster lamps.

What are your instrument lights doing? If the resistor coil in the back of the headlight switch has fried a wire and is contacting the park light wire, that may be your source and explain the dim light. But doesn't explain it only happening with the ignition switch on.

It may be crossing over in the gage/instrument cluster some way. The gages go hot when the key is on and this may be feeding backwards through the instrument light circuit to the parking lights. This sounds probable.
 
I have swapped gauge clusters also to no avail. I went out in to the garage and played with it for awhile. The park lamps dim with panel light dimmer. So I pulled out the headlight switch. I am gonna swap it tomorrow. After looking at the wiring diagram I think it is getting power from the ignition switch for the warning buzzer. The headlight switch itself seems messed up now that its out and in my hands. I will know for sure tomorrow when I swap on from a parts donor I got in the backyard.
 
The clock is also a possibility. The clock and the radio have a wire that goes hot with the ignition on and both have a light dimmer wire. Unplug the clock and see what happens.
Been there done that on many occasions, battling dash wiring gremlins is time consuming.
The instrument illumination fuse is the farthest right, have a look behind the fuse block. Use a small mirror and a flashlight. Could be something like a candy wrapper causing a bridge behind the fuse block or possibly a wire rub through.
After the third funk up in the instrument illum circuit I bypassed it, jumped the park lamp circuit (behind the fuse) to the instrument illum circuit (behind the fuse) and did away with the dimmer at the headlight switch and a wire. My instrument lights are always on bright now.
 
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