Brake lights constantly on: fixed

bigwinn

bigwinn

Elite
 Lincoln UK
Site Supporter
Afternoon all

Thought I’d have solved this but I’ve hit a dead end

E86 coupe brake lights constantly on. I have a bulb out warning on the dash despite having all voltage monitoring switched off.

I thought also the car was putting the lights on as I had some dtc issues- they are all sorted so that’s not the cause

Is the car thinking there is a bulb out on the brakes so puts all brake lights on?

Have replaced the brake lights switch- no change so I’m not thinking it’s that? How can I test it?

Thoughts?

Cheers

Stuart
 
I assume with the ignition on only?

If you take the plugs off the lights, do you still get voltage on the connectors - just to rule a short out in the light cluster
 
IGN on only yes

Although there is a delay between ign on and the lights coming on- like it’s a reaction to a self test mode versus an immediate voltage

I’ll check voltage at connectors
 
Well I’ve eliminated the bulb out issue as the problem- a red herring

I’ve popped the ABS connector off and cleaned it
Checked fuse 14
Ordered a new brake switch
 
Managed to sit and have a look at TIS to see if I can start to trace where the issue is coming from prior to a new 3rd switch coming

The outputs from the 4 pins at the brake light connector (s29) are

1: from fuse 14 power distribution
2: to earth X1105
3: to pin 16 on the DME
4: to pin 25 on the LCM, to pin 41 DSC and to pin 4 DSC

Thoughts on which ones I should start to look at?
 
When I disconnect the brake switch the lights are still on and stay on

I've tested the pins to the switch in the current ign on state

Pin 1 has 12v
Pin 2 0v
Pin 3 0v
Pin 4 6v

Im now thinking the switch isn't the issue as when its taken out of circuit the lights are still on
 
Dodgy earth at the lights somewhere? Sounds like a 70s Ford problem
Is it coded for daylight running lights?
Maybe putting brakes on instead of sidelights?
 
FFS

I hate fixing other peoples f**k ups

Went to look at the wiring on the lcm

Spotted a loose cable that had been previously cut going to pin25 (not one I’m looking at to be fair) which looks like the aftermarket cruise loom install

Found some wires floating and reattached

Brake lights now work perfectly
 
bigwinn said:
FFS

I hate fixing other peoples f**k ups

Went to look at the wiring on the lcm

Spotted a loose cable that had been previously cut going to pin25 (not one I’m looking at to be fair) which looks like the aftermarket cruise loom install

Found some wires floating and reattached

Brake lights now work perfectly
Click to expand...
Had you upset the person you bought the car from Stuart?😀
 
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