Please help electrical fault

[Darf82]

Hi guys thanks for your time.

I'm new to the forum so hi 👋

My wife's car is a 2009 1.6 D zetec

Right the problem I have is when I put my rear demisters on it doesn't work but it comes up on my dash saying rear luggage compartment open. Also when I look outside when the switch is on the centre brake light comes on and rear wiper doesn't work.

Switch the rear demisters switch off and rear wiper starts working and brake light goes off but still rear demisters doesn't work.

Also when I hit my brake pedal it comes up on dash luggage compartment open.

I've opened all the back up and spray all switches with silicone spray. (Wiper/boot switch/rear lights)

The boot switch still works with button and keyfob.

I had a feeling it may be foot brake switch but the brake lights all work fine when the rear demisters switch is off.

Please can anyone help

[JW1982]

You should check the wiring harness to the tailgate. The problems you describe are often caused by broken wiring or damaged wiring insulation. This kind of damage usually occurs inside or near the rubber boot between the tailgate and the body of the car.

[Darf82]

Ok thanks. I'll have a look.

On the odd occasion I press the rear demisters switch it flashes the stereo lights on for a split second

[Tdci-Peter]

5 hours ago, Darf82 said:

the problem I have is when I put my rear demisters on it doesn't work but it comes up on my dash saying rear luggage compartment open. Also when I look outside when the switch is on the centre brake light comes on and rear wiper doesn't work.

Centre brake light, rear wiper, rear demister and the rear locking (including door ajar signal) all share a common ground wire from C950 (The rear demister ground connector) to earth point G77A (Left wheelarch ground). It must be a break in this wire, the given symptoms exactly match. Probably, as Wilco says, in or near the flexible joint where they cross from tail hatch to body.

(It may also be upsetting the number plate lamps, but I doubt if anyone would notice that!)

[Darf82]

Thanks again will have a look tomorrow. Number plate lights seem to be fine.

I will add when I press boot switch the centre brake light comes on too. I will check wires tomorrow.

[Tdci-Peter]

33 minutes ago, Darf82 said:

I will check wires tomorrow.

Getting inside the wiring looms can be a real pain. I think I would try to locate the ground end of the demister inside the tailgate, then run a new cable (2.5 mm sq min) to any handy earth point on the body. I think it can be pushed trough the grommets on the tailgate and ty-rapped to the existing bundle. Short circuits to body are not a problem, the worst that can happen is the new wire will chafe through & break, but then you will be only back to where you are now.