Hello all

New member here.

I have a 2006 UK coupe and the brake lights are all out. I have replaced the brake light switch and still no joy. Any ideas? Is there a brake light relay to check? I couldn’t see one on the wiring diagram and I did a search through the forum but couldn’t exactly ascertain where it might be.

**Sorry should add that I have checked the fuse in the dash fusebox…

Thanks everyone.

 

Two things:
1) The "brake lamp switch" at the pedal does not, apparently, directly activate the brake lights. IF we can believe the service manual, (not sure we can) that switch is used to enable shifting out of park but apparently not turning on the brake lights. There is an output from the brake controller that triggers the brake lamp relay when you press the brake pedal.

2) So the fuse is good, is there POWER to the fuse? THere should be power to that fuse anytime the key is in the "ON" or "Start" positions, but not when the key is off.

Next, the brake lamp relay is in the underhood fuse box, it is triggered by a switched ground from the Brake controller. If there is power to the fuse, then I'd want to see if the relay is being triggered when you hit the brake.

 

To access the brake lamp relay, see section 7.5 of this document.

 

Thanks so much for your response Pizzaguy.

There is no power to either the fuse or the relay. Whilst digging around under the footwell I found a damaged and loose ground (what we would call earth) cable. I assume that the only ground cables leaving the footwell would be for the horn and for the brake signals. Since the horn works fine I think this might be the source of my problems. Is my assumption correct?

I cannot access behind this cluster of cable at all and so I thought I could route a cable direct from the relay back to a join with this loose wire. Am I right in saying that the ground from the brake switch (and hence this cable) goes straight into the relay at pin 85?

 

 

 

No power to a fuse is not a ground problem, its a problem with getting power to the fuse.
You MUST determine why there is no power to the fuse, that feed comes from a wafer on the ignition switch. I believe the high side of the fuse goes to one of the tiepoints (splice block 101) at the back of the fuse box, those are fed by the switch.
FIRST, make sure your voltmeter readings are valid, try measuring another point that you know is powered up to verify your meter is good. Make sure the ground you have your meter connected to is a REAL ground.

The manual shows a diode on the high side of that fuse, if the diode is burned open, you'd have no power to the fuse. It is not common, but it is possible that the diode is blown.

 

Hi Pizzaguy

So there is power to the fuse. I struggled to find a decent ground.

The relay does not trigger. There is 12v power to pins 30 and 85 with the ignition on. I have tried changing the relay and still no luck.

 

That is what I expected to hear from you. It's not the first time a poor ground misled someone.

The switched ground to pull in the relay comes from the brake controller, so that is your next item to check. See the service manual: Wiring chapter>Rear LIghting. Unfortunately, there is little service information on the brake controller.

 

Hi Pizzaguy

So I jumped the relay to see if the lights would come on and they didn’t. I found a short at the left brake light, fixed it and voila all lights on.

However still no lights when I press the pedal. So I must have had two faults and that is what held me back.

Anyway, checked brake switch and there is power there, relay is fine and so the next port of call must be the brake controller module like you said. I think it is this thing that I have taken a photo of but it looks totally different to the service manual 🙄

Is this the right thing? The manual says cavity one needs checking for voltage….

 

 

YEs, that's where the signal to pull in the relay comes from. That pin you mention is pulled to ground by the controller, which then causes the relay to pull in.
Its a simple system, unless you get into the internals of the brake controller....

 

Hi Pizzaguy. By way of an update, I gave up trying to figure out the brake controller outputs and so just ran a new wire to the brake relay from the brake switch. It works fine and maybe one day I will return to trying to figure out the controller. However I must have dislodged something, possibly in the illumination module, and now the dash lights, radio lights and turn signals don’t come on 🙄

Any ideas? I searched the forum to no avail.

Thanks for all of your help so far…

 

Hi all

Resolved the turn signals and dash lights not working by using adhesive on the purple harness to the illumination control module to hold it in place tighter. Hope this will help someone…

 

That is very odd. If you want to help, tell/show us where the adhesive was applied. ANd I wonder what you did to impair the ICM.

 

Hi Pizzaguy

ah apologies I should have taken a pic before replacing but the chain of events is something like this…

I had a brake light malfunction and I took out the ICM for testing.

The ICM has a large grey harness which opens by pressing a clip and pulling upwards, ditto a black one, a purple small harness with top and bottom clips and a really small black slide out at the end.

The clips on the purple one are really brittle and the top one snapped but I thought I had secured back in place using only the lower one. After a few days I noticed that the turn signals, dash lights and console lights weren’t functioning. I went back to the ICM and noticed that even a slight movement in the purple harness could make them malfunction. A little drop of glue at the top of the harness, held in place with a vice until setting was enough to hold it more securely.

If anyone has the same symptoms, the purple harness would be the place to start. I couldn’t determine if there was a fuse associated with that system.

 

Well, in that case, it's not likely this will be repeated. Failure IN the ICM are somewhat rare, but not unheard of.
I prefer the wiring of my Ford Ranger - totally easier than the Crossfire. What an overdesigned mess.