88 Gt No Brake Lights/ No Left Rear Turn Signal


New Member
May 3, 2014
This is my first post here, so I'll try and keep it simple.

I have a 88 GT 5.0 5speed. I just found out my brake lights don't light up, nor does my left rear turn signal work. First, on the turn signal, I have power to both rear turn signals and I did a continuity test on the ground. On the brake lights I have already replaced the brake light switch, verified power to both sides of the switch.
When I got the car back in April, I had hazards, but no turn signals so I replaced the multifunction switch with a repro from NPD which didn't fix the issue, come to find out the flasher for the turn signals was hidden under the steering column, after replacing that I had signals. Do you think the multifunction switch is the problem? If not where else should I start looking?

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i'm familiar with penetration
Mod Dude
Feb 18, 2001
If you have power and ground at the turn signal, it should work then. Did you check the bulb?

maybe your wording is confusing me, but when you put your turn signal on, i took it as you verifies that you do get 12V at the bulb socket that should blink the bulb? Is that correct? Then the issue is at the socket/bulb.


New Member
May 3, 2014
Yes I checked the bulb, I swapped it with the right side bulb. When I turn on the turn signal I get 12v at the bulb socket as it blinks.
Does anyone know if the brake lights run through the multi function switch?


StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
Dublin GA
Brake lights don't run through the multifunction switch.

PM me your email address and I will send you a complete Ford Factory 89 Mustang electrical diagram set.

The 88 and 89 body wiring is the same.The zip file is 2.5 MB and is too big to fit through Stangnet's email gateway.

89 Mustang wiring diagrams zip package–

They are in a zip file format to reduce the size of the package. If you don't have Windows 7 or Windows 8, you’ll need WinZip or other Windows archive tool to extract them from the zip file.. See www.majorgeeks.com - Download Freeware and Shareware Computer Utilities for a free download.

The diagrams show the location area and the connectors are drawn to the same shape as those in the car.

You will need the Adobe Acrobat viewer which is also a free download – www.adobe.com/products/acrobat/readstep2.html - Adobe Reader download - All versions
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