Mark Mcclintock

We have a 1986 928s and when you hit the brakes the rear wiper turns on. We have tried everything and nothing is working

Ed Scherer

I'd be looking very carefully at grounds. Usually, when you've got strange interaction between two things that seem like they should be unrelated, it's an open ground. I believe the ground point involved here is MP VI. The usual situation is that some ground wires are connected together, but they're not connected to chassis ground properly at the ground point.

I'm guessing (but not sure) that MP VI is the same for an '86 as for the '87 below.

See also some additional diagrams.

docmirror

Locate the tool panel in the rear hatch, just below the lower lid, and twist the two black ***** 90deg and take the panel off. On the driver side, behind that panel there is a relay that controls the rear wiper. Remove that relay(or disconnect it). Test the brakes with the engine running. If they do not make the wiper run, your problem is in the pick circuit from the brake wire, to the rear wiper relay, or the return ground from the relay back to the chassis. If you just want to drive without having the wiper run, leave the relay out. Use a DMM to find the cross voltage(or ground plane) which is being triggered to pick the relay, and cause the wiper to run.

OBTW - if you "tried everything" why ask here?

kombatrok

Probably not helpful, but delete the rear wiper... they suck anyway!

SteveG

If you (or anybody else) delete the wiper, can I have the plastic caps that cover nuts or bolt heads protruding above the hatch?

spooledx2

By everything I'm sure he meant everything we could think of at the time. Thanks for the input, I will try that and see what the results are. I've deleted the wiper on mine ages ago, but we are working on this for a friend that wants to keep it.

Thanks again.

linderpat

Steve, I have a bunch of these. I can bring them to Hershey and you can pick the one that fits. There are different style for different years. Alternatively, Roger or 928 Intl sell them for a couple of bucks a piece.

SteveG

delete