Strange rear window wiper electrical issue (FJ62)

[LtcOliverNorth]

Trying to troubleshoot a strange electrical issue with my rear window wiper. When I open and close the rear hatch, the wiper does not work, but I can get it to start working again if I follow the sequence below:

1. Turn on rear wiper at switch, rear wiper does not work.
2. With wiper switch in the on position, the defroster light comes on too (even though the defroster swtich is off).
3. Leaving the wiper switch in the on position, go the rear hatch and open it.
4. Once rear hatch is opened, wiper starts working.
5. Wiper now turns off/off and works in intermittent mode from the switch as nomal.
6. Defroster light has turned off on its own, and defroster switch sems to be functioning normally again (swich on - light on, switch off light-off).

See video below for the full sequence in action:



The wiper will stay operational even after the car is started and stopped multiple times, but as soon as I open the hatch again, the sequence must be repeated to get the rear wiper to start working again. (Front wipers unaffected.)

I've cleaned the connector at the wiper motor and tested ground at the wiper motor, all seems good. I even swapped in a spare rear wiper relay (green box) to see if anything would change; it did not.

Any ideas of what might be the cause?

 

[Eurasiaoverland]

IIRC the rear wiper and defroster share an earth point (6 mm ring terminal) on the rear sill (just behind the fuel tank), so you might want to check that. I would also check for wires which have become nicked where the go between the body and the tailgate.

 

[3_puppies]

I'd be checking the wire harness where it goes from the roof to the hatch
and/or the plug inside the roof where the harness connects

 

[3_puppies]

IIRC the rear wiper and defroster share an earth point (6 mm ring terminal) on the rear sill (just behind the fuel tank),

I'm thinking that ground is for the license plate lights, all the hatch wires run thru from the roof up by the hinge

 

[Eurasiaoverland]

I'm thinking that ground is for the license plate lights, all the hatch wires run thru from the roof up by the hinge

Ah ok, mine has swing out doors and all the electrics (including for a rear wiper which was never a feature on swing-out door models) are routed behind the fuel tank.