Brake light malfunction + cruise control

TeamSAXON · 10-02-2019, 12:32 AM

Hey I have a series 3 xr6 172kW that's got a couple of issues now which have come up in the last few days.

The cruise control used to function fine but now it will only turn on, the speed cannot be set with either + or -. I have replaced the master cylinder brake switch but this hasn't fixed it.

I have read it could be the brake pedal switch, but I only have very novice level knowledge and don't want to stuff around with anything that could make things worse.

Which brings me to the next issue:
I also recently changed the tail lights from halogen to leds. I had these same leds (taken directly from the wreck) set up in my series II XR6 and never had voltage leak issue.

The brakes are continuously lit when the headlights are switched on. Otherwise they operate normally.
I should point out the spoiler lamp operates normally when the headlights are switched on. Would this mean that the brake switch is not the issue?

Possibly dirty or corroded bulb sockets??
Have not tried an ecu reset yet.

Don't really have the cash to spend on an auto electrician

raceteam · 10-02-2019, 06:19 AM

The LEDs are not earthing correctly - some are just badly wired and the stop/tail circuits are connected with a resistor (very bad). Pull them out and stick normal globes back in.

TeamSAXON · 10-02-2019, 12:10 PM

Quote:

Originally Posted by raceteam

Pull them out and stick normal globes back in.

I should point out that the leds functioned perfectly the night I put them in. They dimmed and lit when brake pedal applied.

I stuck the halogens in last night but the problem remains.

raceteam · 10-02-2019, 12:20 PM

Unless you've opened the LEDs up, or can confirm that each circuit is diode protected, I wouldn't use them. A bunch of the cheap ones just have different resistor values from each of the stop/tail circuits to a single LED group. This means current can flow through the resistor network between each of those circuits, linking the 2 circuits. The resistors overheat and burn out, and the backfeeding of the circuits does wonders for other components in the vehicle.

Basically, the resistor network in the LED burns out, and the tail lamps are backfeeding the brake light circuit, bypassing the switch.

You described 2 different problems (brake lights on, and cruise no go), do they both remain with the incandescent globes back in?

snap0964 · 10-02-2019, 01:01 PM

Quote:

Originally Posted by TeamSAXON

I stuck the halogens in last night but the problem remains.

I hope they're dual filament bulbs - single filament will cause what you describe.

Citroënbender · 11-02-2019, 12:15 PM

Is the car a manual?

(There is a reason for this question.)

snap0964 · 11-02-2019, 06:22 PM

Yeah, the clutch pedal cancel (if fitted) and the mast cyl switch should be normally closed.

deeppocket · 15-02-2019, 11:29 AM

Quote:

Originally Posted by TeamSAXON

Hey I have a series 3 xr6 172kW that's got a couple of issues now which have come up in the last few days.

The cruise control used to function fine but now it will only turn on, the speed cannot be set with either + or -. I have replaced the master cylinder brake switch but this hasn't fixed it.

I have read it could be the brake pedal switch, but I only have very novice level knowledge and don't want to stuff around with anything that could make things worse.

Which brings me to the next issue:
I also recently changed the tail lights from halogen to leds. I had these same leds (taken directly from the wreck) set up in my series II XR6 and never had voltage leak issue.

The brakes are continuously lit when the headlights are switched on. Otherwise they operate normally.
I should point out the spoiler lamp operates normally when the headlights are switched on. Would this mean that the brake switch is not the issue?

Possibly dirty or corroded bulb sockets??
Have not tried an ecu reset yet.

Don't really have the cash to spend on an auto electrician

My similar problem was the wiring going to the trailer plug. The wiring was too close to the exhaust & melting it. I've been told it's a common fault. The plug wiring not necessarily the exhaust issue.

Sent from my Moto G (5) Plus using Tapatalk

LPGUTE · 15-02-2019, 01:27 PM

if the brake light is out(less resistance in the circuit) it will stop you setting the speed for the cruse control leds(less resistance then a globe thus less resistance in the circuit) can make it do similar thing if a resistor is not added. does it fix the problem when you put every thing back to stock?

11ford11 · 15-02-2019, 01:38 PM

Refit standard lights and then check stop light fuse and switch