Electrical Weird horn - headlight issue

[Kuwait-Foxbody]

Hello everyone,

I recently replaced the headlight harness on my 1987 Foxbody GT with a Ron Francis harness that is designed to fit 1987 to 1990 models. Unfortunately, after installing the new harness, I have been experiencing several issues that I need some advice on.

1. **Side Markers Always On**: I noticed that the side markers stay on on ignition even when the headlight switch is turned off. This is quite concerning as it's clearly not functioning as it should.

2. **Horn Issue**: The horn has stopped working properly. Instead of the horn sounding, I only hear a clicking noise from the relay when I press the horn button.

3. **Strange Behavior with Fog Lights**: When I turn on the headlights and then switch on the fog lights, the horn suddenly starts sounding without me pressing the horn button.

Has anyone else experienced similar issues with the Ron Francis harness, or does anyone have suggestions on what might be causing these problems? Any guidance on how to troubleshoot or fix these issues would be greatly appreciated.


Thanks

 

[Noobz347]

You have a wiring problem.

Do you know how to use a multi-meter?

 

[Kuwait-Foxbody]

You have a wiring problem.

Do you know how to use a multi-meter?

Yes..

I tested the Resistance between light switches and Horn fues and it seems that they are connected together

Also when I tested the resistance between horn connector and both horn fues and horn relay it shows overload in the multimeter

 

[Noobz347]

Start with the marker lights. Figure out where power is getting to those lights with the switch in the [off] position.


I see two possibilities:

1. The wiring is incorrect (regardless of what the instructions indicate - they are fallible)
2. You have a broken/missing ground someplace and power is finding another path to ground (perhaps through the marker lights)

Do not discount the possibility of something shorting out in [any] of the light housings. They've been messed with so, they are suspect. Right down to each bulb and socket.