Lighting issues

[87fbmustang]

Hello all! The FB I'm working on has a very inconsistent issue with the lighting. The current issue I am facing is the parking lights turn on with the brake lights. It's a sporadic issue, it isn't wired that way as far as my diagnosis can tell. The courtesy light also stays on and kills the battery. I have tried almost everything I could find on ALLDATA (short of rewiring everything and replacing the switches,) but to no avail. Any ideas?

 

[Mustang5L5]

All parking lights? The rear or fronts only? What year?

SO if you step on the brake pedal, the brake lights illuminate as well as the parking lights? The rear bulbs are duel filament bulbs. Can you tell if the rear parking lights are also lighting up?

 

[87fbmustang]

All parking lights? The rear or fronts only? What year?

SO if you step on the brake pedal, the brake lights illuminate as well as the parking lights? The rear bulbs are duel filament bulbs. Can you tell if the rear parking lights are also lighting up?

It's the front parking lights and the brake lights, however the rear running lights do not turn on with the brake pedal. '87 LX Convertible AOD

 

[Mustang5L5]

What happens when you turn on the parking lights? Do front and rear go on?

The brake and parking lights don't really share any wiring. The front and rear parking lights connect as a splice and separate, but all go through the headlight switch.

DId you try disconnecting the heaflight switch from the harness and then stepping on the brake? Do the parking lights still come on? If so that leads to a wire being cut/sliced elsewhere in the harness that shouldn't be where it is.

Stop lights are completely seperate. So somewhere there is a wire out of place or some hackery has taken place

 

[Noobz347]

So...

Look for unauthorized wiring and splices.

 

[Gint]

Sounds crazy , but try temp regrounding both.. seen this happen many times

 

[AeroCoupe]

Had a buddy put either single element bulbs in a dual element socket or visa versa and it caused all kinds of problems. Might want to pull the bulbs and make sure they are the correct ones.

 

[Noobz347]

Or just flat-out replace them all with the correct incandescent bulbs.

Various El-cheapo LED bulbs can cause havoc too.