Brake Lights Not Working

[BlackStang00]

This one is a little strange. Last night I drove my 02 gt 40 miles no problem. Today I get in it to go get the oil changed and the brake lights, turn signals, hazards and the radio audio don’t work. Even the third brake light won’t light up. The radio powers up and works otherwise but there’s no audio. I got a bump and it started working again for a bit then it quit again. I know most of those functions are tied into the multifunction switch but what are the odds? Anything I can test?

On a side note, I found out that the previous owner used gear oil in the trans. Can I dump it and fill with synchromesh or is it trashed? I think the previous owner of the car used to race it and it might have been supercharged as well. If I had to guess I’d say the trans was making noises and the genius po put in gear oil to quiet it. It shifts fine but is notchy.

 

[01yellercobra]

First thing I'd check are the fuses. Maybe one popped. After that check all the grounds under the dash. Maybe you kicked something on accident.

Drain the fluid and look for glitter. If you don't see any refill it with a decent ATF. Hopefully you'll be ok.

 

[BlackStang00]

All fuses were good. It all started after I swapped out my reverse light bulbs. I’m wondering if a pinched something. Also the brake switch is open, I have another on order. I’m hoping it’s something stupid. I have a new mfs on standby too just in case.

I’ll do that too. I haven’t had time to change my oil (and I live in an apartment) so I went to Ford and had them change the oil and trans fluid. They found the gear oil and buttoned it back up. That’s what scared me. I know the 3650 has issues with synchros as is, hopefully it didn’t mess anything up.

 

[BlackStang00]

I’ve been working on this and still haven’t gotten anywhere. I’m getting power to the brake light switch, mfs and turn signal flasher but nothing beyond that. I tried another new flasher which didn’t do anything. Funny thing is, I took the relay for the wipers and plugged it in. There’s still no turn signals but when I turn the hazards on my tail lights, 3rd brake light and front turn signals light up and stay lit. That means the brake light circuit is fine. Im at a loss right now.

 

[01yellercobra]

The third brake light shouldn't come on with the hazards. Are they blinking or just turning on and staying on.

 

[BlackStang00]

All of the turn signal/brake lights come on and stay on along with the third brake light. No flashing. I find it hard to believe that both flashers could be bad but I don’t know what else to think. Since all the lights work, all circuits are intact. That’s why I’m focusing on the flasher.

 

[hotcobra03]

This one is a little strange. Last night I drove my 02 gt 40 miles no problem. Today I get in it to go get the oil changed and the brake lights, turn signals, hazards and the radio audio don’t work. Even the third brake light won’t light up. The radio powers up and works otherwise but there’s no audio. I got a bump and it started working again for a bit then it quit again. I know most of those functions are tied into the multifunction switch but what are the odds? Anything I can test?

On a side note, I found out that the previous owner used gear oil in the trans. Can I dump it and fill with synchromesh or is it trashed? I think the previous owner of the car used to race it and it might have been supercharged as well. If I had to guess I’d say the trans was making noises and the genius po put in gear oil to quiet it. It shifts fine but is notchy.

Wiring diagram and tests in our factory manual will help you.


If you don't have one. Use the library.

I use Chiltons library, it host factory manuals free.

I use mid-point library in Ohio.
Link, ,

E resources leads to databases. Than to Chilton library
Log in with library card number,

Any 14 didgets will get you in free.
It is a timed site,,if you pause to long you need to start over at log in.
I bookmarked that page for faster in.

You can copy this also to have in hand like a book.

Good luck.

 

[01yellercobra]

It sounds like you have a short somewhere. Maybe a crossed up wire somewhere.

 

[BlackStang00]

This is the wiring diagram I’ve been using. Current flows from the fuses to the flasher then the mfs. I verified I have 12v on the light blue and white/red wires at the mfs. I haven’t been able to get to any of the wires easily to check for current after the mfs but before the tail lights. Since the parking lights work I know the grounds are fine. And when I use the wiper relay, the brake lights and front turn signals all come on steady so I know that circuit is fine as well. All signs point to the mfs but I have another one I plugged in and it didn’t make a difference. Or the flasher module is bad. Since I’m using a regular relay and not a flasher, it’s powering the hazard circuit continuously but that doesn’t explain why it’s not powering the turn signals when I move the stalk.

 

[03cobra#694]

@Vinnie_B

 

[BlackStang00]

While looking at the fuses for the hundredth time, I noticed fuse 13 was popped this time. I know it wasn’t before because I tested it. I replaced it and the turn signals and hazards work again, but when the hazards are on the third brake light comes on too and stays on. And the brake lights still don’t work. I even jumped the brake light switch and still nothing. It would seem there is a break in the circuit from the brake light switch to s323 in the diagram above. That still doesn’t explain why that circuit gets power with the hazards on.

 

[Vinnie_B]

Sounds like you have a bad Multifunction Switch.

Lightning FastElectrical Automotive Repair
PM Me or [email protected]
Website:https: Lightning Fast Electrical Automotive Repair LLC
Remote or Local (On Site) Technical Repair

 

[BlackStang00]

I have another one that I’ve been using to test as well and I get the same result. I’ll try again tomorrow though just to rule it out. I tried it before I found fuse 13 popped so who knows if maybe it’ll work correctly with a good fuse.

One thing that I thought I’d add is that it has switchbacks in the front and sequential tail lights, fwiw. It was all working fine until I parked it one night and they stopped working the next day.

 

[hotcobra03]

See if you can disconnect sections.
Like rear set up you added.
Or unplug all the lights. The mfs may operate

I have an 07 caravan ..

Fuel pump circuit has a short.
Even with 12volts at pump it doesn't work .
I ran a new wire directly from relay to pump and it works fine .

I also had a bad ground off radiator support by battery,,
Eye hook was cracked and caused my car to freak out while driving after a bump ..

 

[BlackStang00]

To make things weirder, I let the car sit while I worked the past couple of days. I come out to check on it and this is what I found. The hazards operate normally now out of the blue so I checked the brake lights and still nothing. I checked for power at the brake light feed at the mfs and get nothing. I checked for power at the brake pedal switch and nothing. Same thing at fuses 33 and 41. I had power on all of those circuits just the other day. I’m at a complete loss right now. How do I lose power at all these circuits after the car sits? What else can I test?

 

[BlackStang00]

When I plug the brake light switch in and turn the hazards on, the third brake light will light up steady with the hazards flashing normally. With it unplugged, no third brake light. This happens with both the old and new mfs.

 

[BlackStang00]

I took a closer look at fuse 33 and a tiny gap was in it so I replaced it and I have brake lights again! I’m praying after all this stupidity that’s all it was lol.

 

[kazman]

You said this all started when you changed the tail light lamps. Why did you do that? We're they out, or upgrade?

 

[BlackStang00]

It happened after I replaced the reverse lamps but I thought I’d mention that the tail lights were replaced with sequentials. That was done months ago though.

It had to have been multi faceted though because fuse 33 was good at one point since I had power at the brake light switch so it wasn’t always the issue.