1985 Carrera electrical issue...

[carolinatrophy]

Last night I was driving around at night in the rain, and I noticed that when I have the wipers on, all the lights get dim for a split second, at a regular interval that keeps time with the wiper movement.

To clarify, picture the wipers going back and forth, left to right. Every time the wipers get all the way to the left, ALL the lights go dim for a second, and then brighten back to normal again as the wipers move back to the right. This is ALL the lights - headlights, dashboard lights, tailllights... They don't go out completely - they just dim for a split second. If the wipers are on high speed, it still does it, but faster - like it's keeping time with the wipers.

Any idea what I should check?

Thanks in advance,

[cgarr]

I would start with all the ground connections.

[john walker's workshop]

90A carrera alternator/regulator units are famous for overcharging, so you might want to see what your charging system is putting out. a simple voltmeter attached to any 12V source and ground.

[Robert Buchanan]

It is possible that at the end of each stroke (or revolution of the wiper motor) that there may be binding in the mechanism, or a worn spot in the drive gears, or that the bushings in the connecting arms are gone. This slightly "out-of-sync" condition may be binding. This would create the condition of the motor using to many amps as it is pushing harder to complete the revolution. It suprises me that the fuse does not blow if this is might be an issue.

Visibly check the entire assembly for binding. Clean it up and put some lithium grease on all of the moving points of contact. If you can disconnet the assembly from the wiper motor, you can move it all by hand to see if it is moving freely.

Check to see that the correct amerage fuse is in place. If a larger than factory fuse, put the correct fuse in a try the system. If that is good, I would check the amperage draw on the hot side (12Volt) of the wiper motor. I don't know the correct amp draw (maybe someone has a Porsche shop manual and can look this up for us). If the motor nameplate (or stamping) is visible, it will state the maximum amp draw.

911_pilot

[billybek]

All great places to start! Start with the easy stuff and work your way in. If you have a good quality meter, check charging system first (perhaps your fan belt is loose and slips when alt is under higher loads). Check the voltage at the battery when you have a good electrical load on, lights, wipers, heat blowers etc and record your values. Grounds next. If you can run the motor load through your meter to find your amps and compare that to full load. Might be a binding/ mechanical issue.
A good wiring diagram is always helpful.

[carolinatrophy]

Thanks guys! The alternator and belts are all less than two months old, and I used all new factory parts in the swap so I'm pretty confident in the charging system. But I will check i all anyway.

The fuse box is brand new too, with all correct amperage fuses in place, but I'll definitely check for binding. I'm also suspicious of the wiper switch itself, because it does weird things sometimes. For example, if I turn the wipers off they do not complete their cycle and park normally - they pretty much stop wherever they are when I turn the switch off. Or at best they complete only half a cycle and "park" over on the passenger's side of the windshield.

I'll check everything you mentioned and keep you posted. If you come up with any other possibles, let me know.

Thanks again,

[rick-l]

Originally Posted by carolinatrophy

, if I turn the wipers off they do not complete their cycle and park normally - they pretty much stop wherever they are when I turn the switch off. Or at best they complete only half a cycle and "park" over on the passenger's side of the windshield

This would be a good place to look for something.

When you turn the wipers off there is a switch in the motor that keeps it running until the wipers are in the park position.

That is a 25 amp fuse that may momentarily survive a .1 ohm short but if it is shorting inside the motor there should be some evidence. Was the wiring to the wipers changed?

[porschenut]

Originally Posted by carolinatrophy

For example, if I turn the wipers off they do not complete their cycle and park normally - they pretty much stop wherever they are when I turn the switch off. Or at best they complete only half a cycle and "park" over on the passenger's side of the windshield.

Try swapping in a new relay.

[jonbot]

Originally Posted by cgarr

I would start with all the ground connections.

+1 on checking the grounds