Turn signals, hazard flashers, and brakes.

[Nero]

I think that's something for the brake booster, but don't quote me on it. My truck has it too, and my cruise doesn't work ( but that's cause I'm too lazy to install a few wires)
No power, I'd chase it backwards to the fuse panel. Luckily those wires are all close together.

 

[chillman88]

Also, I noticed another switch on the brake pedal. Actually more of a plunger. It seemed to have a hose connected to it as opposed to wires. Would this be to shut off the cruise control? Because I have to cancel the cruise control at the steering wheel. Brakes don't shut it off. I learned that the scary way. ;-)

Yes that is a dump valve for the cruise control. It's possible it's not adjusted properly. If memory serves it should be closed with the pedal up and pushing the brake pedal should open it and release the vacuum.

On my 90 the brakes only kill the cruise if you tap the pedal quickly or if you hold it for a few seconds. If you press the pedal momentarily to slow down for someone turning the cruise takes off when it gets vacuum back which can be quite.... Interesting.

Part of the problem you're having is likely tied into the brake switch not getting power though. There are redundancies in the system, the vacuum dump works along with an electrical signal from the brake pedal to cancel the cruise control. There's also a switch on the clutch pedal (if equipped) and some of them have a pressure switch in the brake system as well.

 

[IDIBRONCO]

There's also a switch on the clutch pedal (if equipped)

He's got a C6. That cruise cancel switch can also leak vacuum. I know that I gained 1" of vacuum when I plugged that hose in my Blue Truck so it was definitely leaking.

 

[Jesus Freak]

Take it to @Selahdoor, he's an electrical genius! And he'll create the most fascinating thread about how he fixed it AND he'll finish the story!

 

[Brian VT]

I'd love to take a trip there. Looks like a nice place to be.

 

[Brian VT]

I went to the fuse panel and tested somewhere that I knew was working.
I got 12.5v from the "left" terminal and, obviously, 0.0v from the "right" terminal.
So now I had a baseline to look for.
I went to the brake lights fuse and on the left side I got 0.0v and the right side I got 0.3v
This certainly explains why my brake lights aren't working.

I guess I need to figure out where the wires to that brake fuse come from? How to do that? I see a contraption that comes through the firewall with a gob of wires coming out of it. I assume my brake wire(s) is in there somewhere. But what to do/where to look now?

 

[Nero]

Should have voltage on both sides of the fuse. If you have no voltage at the fuse, look further up the chain. Brake lights and hazards are constant power. Maybe check your firewall pass through? Could have corrosion.

 

[Brian VT]

The firewall contraption looks clean and solid. And the wire bundles look original and look good.

 

[Nero]

Just to clarify, did you disconnect it and check out the pins?

 

[Brian VT]

I don't know anything about it. So it's like a male/female plug at the firewall?
And I can disconnect it and clean (and test?) the pins?
That sounds like it would be very handy. Any more info. would be appreciated. Like any idea which pin might be the culprit?

 

[Nero]

Ok finally got off my lazy butt and got onto my laptop. Here's a PDF of the wiring diagram for the brake, turn, and hazards. The manual is from AllData, and it looks like a poor scan of the original manual. I checked Mitchell1 and apparently they don't even have lighting diagrams. Hope it helps.

 

[Nero]

I don't know anything about it. So it's like a male/female plug at the firewall?
And I can disconnect it and clean (and test?) the pins?
That sounds like it would be very handy. Any more info. would be appreciated. Like any idea which pin might be the culprit?

Sorry, let's back up a little here. Looking over the schematic and I'm putting my diagnostic hat back on.


Looks like both circuits for the brake and hazards go through the hazard switch.

Do you have 12v at both fuse 1 (for the brake lights) and I think Fuse 5 (for the hazards)? You should have 12v (or whatever your battery voltage is, 12.6v) at all times.

 

[Brian VT]

My fuse chart says brakes and hazard on fuse 1. It says fuse 5 is for turns and backup (which work fine).

Thank you very much for the wiring diagram. You went way above and beyond. Unfortunately, I have no idea how to use it. lol

 

[Nero]

Lol, maybe it's time to loop in someone a bit more technical locally then. Diagnosing wiring over the internet isn't easy.

 

[Brian VT]

I hear ya. Thanks for your time.