Front parking lights

[Overlandmark2020]

I am replacing all the lights on my 89 comanche and the front and side marker lights plus turn signals are not working. Does anyone know where I could start looking to cure this problem? I've already checked the fuses. Thanks

[AZJeff]

You should start by getting a shop manual with the wiring diagrams for your model year of MJ.  Then obtain a multimeter, if you don’t have one, and use it to start chasing down the lighting circuits.

 

There are links on this forum to where you can download the manual.

[Eagle]

First step is to remove the bulbs and use a test light or multimeter to confirm that you're getting power to the sockets. If so, then check the grounds.

 

How did you check the fuses?

 

[gogmorgo]

A multimeter is very useful, and should definitely be in your toolbox, although you should be able to diagnose this easily enough with a test light.

Start by turning on the lights and checking for power to one of the bulb sockets. I’d start with the passenger side marker light because it’s easy to get at and single-filament. Test between the negative battery terminal and the contacts in the bulb socket. When you touch one contact, the test light should come on nice and bright, or else you should be seeing pretty near battery voltage, and you shouldn’t see anything at the other contact. If it’s good move on to the ground side. Test between the positive battery terminal and the other contact. Again, the test light should come on nice and strong or else you should see near battery voltage. My guess is there’s a grounding issue because it affects multiple circuits, but you don’t know that without testing.

 

This is where the circuit diagrams become useful. Once you’ve isolated the issue, you start narrowing in on it. The first place I would look is the header panel harness connector, located under the airbox. Both power and ground go through it. If you live anywhere that sees salt, there’s a good chance it’s got some corrosion issues. If everything looks good inside, you can then use the wiring diagrams to make sure you’ve got good power and ground where it’s supposed to be at the connector, and if you do, then you’ve narrowed the problem down to the header panel harness. 

 

If it’s a power supply issue, remember that the taillights should come on with the parking lights. If they don’t, I’d suspect the headlight switch, it’s a common issue.