Lighting issues

87fbmustang

New Member

Mar 20, 2025

3

0

1

Westminster, MD

Apr 11, 2025

#1

• Apr 11, 2025

• #1

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

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,144

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Massachusetts

Apr 11, 2025

#2

• Apr 11, 2025

• #2

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

New Member

Mar 20, 2025

3

0

1

Westminster, MD

Apr 11, 2025

#3

• Apr 11, 2025

• #3

Mustang5L5 said:

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?

Click to expand...

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

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,144

17,839

224

Massachusetts

Apr 11, 2025

#4

• Apr 11, 2025

• #4

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

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

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Apr 11, 2025

#5

• Apr 11, 2025

• #5

So...

Look for unauthorized wiring and splices.

 

G

Gint

New Member

Mar 27, 2025

2

0

1

Auz

Apr 11, 2025

#6

• Apr 11, 2025

• #6

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

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

5,755

3,900

183

Claremore, OK

Apr 12, 2025

#7

• Apr 12, 2025

• #7

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

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

42,878

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Box behind Walmart

Apr 12, 2025

#8

• Apr 12, 2025

• #8

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

Various El-cheapo LED bulbs can cause havoc too.

 

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