Mk7 transit T350 Brake lights not working blowing fuse constantly

[Aaron C]

Hi All! Signed up to ask this in case its one of those "oh they all do that" things. Realised my 3 brake lights were not coming on in a beater of a transit i bought cheap. ABS light is illuminated along with that cog icon that i understand is to do with the injection system. fuse was blown, replaced it and it blew again. Checked continuity on the pins for the brake circuit at the lamps and get a short but i assume thats just because its a closed circuit, changed the brake pedal switch, seemed to fix it then 2 mins later fuse went again. Any tips on where to look next?

[unofix]

I assume the fuse only blows if you put your foot on the brake.

Start by replacing both the left and right brake light lamps. Sounds like one of them may have an internal short-circuit.

[Aaron C]

On 8/26/2022 at 7:31 PM, unofix said:

I assume the fuse only blows if you put your foot on the brake.

Start by replacing both the left and right brake light lamps. Sounds like one of them may have an internal short-circuit.

Thanks for the advice. Thought it worked at first, disconnected the dodgier of the rear lamps, popped in a fuse all good other two lit up. Ran it on drive for 30 mins pressing brake at random, fine. Went for a drive, got suspicious it had popped. Pulled up to check gone again. 

 

Decided to disconnect lamps one at a time with brake pedal depressed changing fuse each time. Fuse would immediately blow even when no lamps connected.

 

Next plan?

[unofix]

If the fuse blows with all 3 lamps removed then you have either (a) wiring fault to earth from the brake light switch to one of the lamp holders. Or (b) you have a faulty lamp holder.

Disconnect the wiring plug from all 3 lamp holders. Does the fuse still blow with nothing connected ?

[Aaron C]

5 hours ago, unofix said:

If the fuse blows with all 3 lamps removed then you have either (a) wiring fault to earth from the brake light switch to one of the lamp holders. Or (b) you have a faulty lamp holder.

Disconnect the wiring plug from all 3 lamp holders. Does the fuse still blow with nothing connected ?

Sorry I wasn't clear, I had plugs pulled from all lamp holders, I'm guessing I look for short to earth in wiring?

[unofix]

Yes. If all lamp holders are disconnected then the fault has to be with the wiring. Somewhere between the brake light switch and the lamp holders.