VAXHeadroom

Brake lights are not working. Here's what I've done so far. Any help would be appreciated!

1. Pulled brake pedal switch and checked it. Took it apart and cleaned the contacts - ohm-meter now shows good operation. still no lights.
2. I have running lights so the common ground is good.
3. STOP fuse is good.
4. White connector on the brake pedal switch has 12v across it.
5. Black connector on the brake pedal switch has no voltage across it.

Does this switch drive the lights directly or is there a computer connection involved? I couldn't figure it out from the manuals.

I think I'm down to a harness problem. Anybody mucked with this before?

Thanks,
Emory

Icemark

There are two switches on the P package verts, one that is brake and one that is cruise control.

If you have leather seats, or seats with headrest speakers you have a P package vert.

The circuit works by 12+ volts into the switch, 12 volts out of the switch when the pedal is pressed.

The signal then goes to the CPU in the drivers kick panel, and from there feeds to the brake lights and idiot lights on the dash.

VAXHeadroom

I do have the P package. Any idea what's inside the CPU? Is it a power transistor or something that drives the back lights? And should I see 12V on both connections?
THANKS!! (I was hoping you'd pipe up in here! )

Emory

pyroal188

im no professional but when i had loose wires from my aftermarket radio the tail lights and dash light would go out if i moved the radio too much. so i taped them up.

but strangly my radio wouldnt go out.

i dont think that will help u much but u never know

Icemark

Yes, it is a looped transistor. The circuit inside the CPU, monitors resistance, when it see's the resistance high or too low, it turns on the stop light in the idiot lights.

You should see 12+ volts on Green/White at the switch all the time. On the White/Green wire at the brake switch and the bottom of the CPU (4 pin plug) you should see 12 volts when the brake is pressed.

Also on the sold green coming out of the CPU's 4 pin plug should have 12 volts+ when the brake is pressed.

VAXHeadroom

Thanks that's a huge help
Also: Do you know if the CPU is the same between an 88 vert and an 86 coupe? (since I have a parts car!)

Emory

Icemark

Yea, on the 88 vert you can use either a FB01 or FB05 CPU. They both plug in (and if you use a FB05 CPU it will add lighted ignition key, without adding anything else).

VAXHeadroom

I have a lit ignition key now, so I'm guessing that's an FB05...
I'll get back to it probably Thurs night, so I'll let you know what i find!

Thanks again!

Emory

VAXHeadroom

Finally got it fixed!!
Bad solder joint on the CPU Brake module!
For future reference, here's the full pic set.
Oh, and before that - the pins for the brake line should show about a half an ohm when this is working correctly.

CPU Housing with modules removed. They just slide in here!


Bottom of Stop/Warning unit showing broken solder joint (nearest left corner)


Fixed!


Top of Stop / Warning Unit.


Other side. The wierd plate standing is apparently a large power resistor - about a half an ohm.


Thanks to ICEMARK and all the FAQ writers!!

Emory