Brake lights turn on by themselves and...

[J.Lo]

Hi guys,

Our 2004 Td5 Defender has developed a bizarre electrical problem.

When parked and locked the brake lights sometimes turn on and off randomly. I have caught it doing this twice now.

When it happens I can unlock the vehicle, and if I press the brake pedal the instrument cluster lights up as if though the key was put in the ignition and turned. Even the fuel pump runs.

If I do put the key in the ignition and turn the engine starts normally.

After some time the lights turn off again.

Does anyone have any experience of this or ideas on what could be causing it?

Thanks, Jeff.

[DazzaTD5]

While the obvious thing would be a faulty brake switch, or faulty ignition switch, each one doesnt explain what looks like two seemingly different faults.

My thought is certainly a poor earth somewhere, go over all the ones you know of, neg to chassis, engine etc etc, ensure all are clean and tight.

A few months back I did a clutch on a Defender TD5, done it a million times, all back together, running fine, parked it up, went to turn it off.......engine kept running.....
then I noticed on one side the indicators were on solid, the brake lights came on with the tail lights etc etc. Odd things like that and I always look for a bad earth. In this example I had missed putting back a small earth on the drivers side about level where the transfer case is, that went from the top of the chassis to the box (I had tucked it out of the way when pulling the box down). Connected it back up, all perfect.

So.... short answer, look for a bad earth.

Regards
Daz

[waltsd]

My d1 did that this week. Was a couple of wires in the way of the b switch. Must have slipped down while putting cb radio in. So check if b switch is being affected.

Sent from my GT-S7500T using AULRO mobile app

[J.Lo]

I found that by pulling the fuse for the brake lights the cluster lights could not be energised by the brake pedal which hints that I have something funny going on between the brake switch and the brake lights.

The lights are at full brightness so the fault is making a very good connection. It actually flattened the cranking battery on me over several hours last night.

I had a look at the ECU and noticed that there was a lot of oil around the red connector. Pulled out the ECU and washed it down with shellite, and then washed the connector, loom, and general area. Looks like I need to replace the injector harness. And as per the forums will need to flush the connector and loom a few more times too. The red connector on the ECU came up very clean with no oil leaching out of it so I'm going to assume that oil did not get inside the ECU enclosure - maybe wishful thinking.

Also noticed that in the brake system I have some sort of 3rd party trailer brake controller. I've got my suspicions about it as the wiring is messy but have little experience with such devices. It seems to have power running directly to it via an inline fuse. I imagine it ties into the brake light circuit, so it does have the potential to back feed power to the brake lights. Has anyone else experienced this?

In the mean time I'll check all the earths I can find. The actual brake switch itself seems to be working fine.

Appreciate all hints and tips.

[Don 130]

If you've got an electric trailer braking system fitted, get an auto electrician to check it for you. I don't know how you'd do it , but very soon after we had a teconsha unit fitted to one of our vehicles, we had the same problem as you. A phone call to the bloke who put it in resulted in it being replaced with another brand. (red arc) His comment at the time was that he was sick of this happening and wouldn't be fitting them again. That was some years ago now, so things may have changed.
Don.

[J.Lo]

Don,

I think you've hit the nail on the head. The controller is a grey labelled Tekonsha Voyager.

Just cut every wire in and out of the thing.

Google searching this controller shows it's notorious for powering brake lights and flattening batteries.

I'll rip it out soon and replace it with another. Has your red arc behaved itself?

Fingers crossed, my brake light woes could be over, although now have an injector loom to replace :-(



Cheers,
Jeff.