300 TD Rear lights, wiper always on

I have a 1990 300TD wagon, and an intermittent problem has become permanent. Before, when I put the car into revese, occasionally the rear wiper would turn on. Then occasionally, when starting the car and running forward, sometimes the wiper would also go on. Now the rear wiper and the reverse lights are on whenever the ignition key is turned. I pulled out the reverse lamps and the relay for the wiper (located in the rear hatch) and that has at least bought me some time, but I would like to fix this electrical gremlin.

Another clue, is the rear lights in the car (set of four on the pillars), which normally go on when the rear doors are opened), now also go on and stay on (but dim) when the reverse lights and the wiper is going. It used to be that opening the rear hatch would turn the rear lights on for a moment, then they would go off. I searched for some type of microswitch for the lights in the rear hatch but found none. Where is the switch?

Other minor electrical issues that may be related:

sometimes the glow plug light doesn't illuminate when the ignition is turned on. most times it does what its supposed to.

Any help appreciated

[Amge55]

I believe you have a host of electical problems crossing each other. Can't help you there. What I can tell you is that on the TE/TD wagons, the rear wipers have a smart feature: If you have the wipers on the windscreen, when you put the car into reverse, the rear wiper will come on automatically. It assumes that since you activated the front wiper, the rear one will do so when you need to go backwards. This automatic feature, along with your other problems is probably complicating the diagnosis.