tilac999

I can have one or the other but not both. I disconnected the wiring to the rear wiper so I can have a horn. If I reconnect the rear wiper and activate it, the horn fuse blows. It parks in the correct spot and was working fine until I had a problem with my battery ground strap which has been replaced with a new one.

MainePorsche

First socket output from the horn relay is at T25. T24 is for the rear wiper. See if any inadvertent contacts at the CE board here.
From horn Relay XII socket output T25 goes to pin 53a at the wiper motor. Relays X Fresh Air Blower, XIV Starter, XVIII Auxiliary Sensor are identical to Horn Relay XII. Swap one out for the Horn Relay and see if function is normal.

BRB-83-911SC

Brad - has the car been starting reliably since the ground strap replacement? Any chance you disturbed some wiring near the rear wiper motor when replacing the ground strap? No idea why it would affect the horn fuse though. Once the horn fuse blows, does your wiper still work?

MainePorsche

The Horn (Fanfare) fuse # 18 is on the T25 line. See WD 97-217 for 1985.

Alan

Firstly does the wiper work on its own ? and when the fuse isn't blown - does the horn work on its own?

These aren't really related circuits but hey share the same fuse - so could jucst be an issue with the rear wiper - otherwise I think the proximity on CE plugs sounds the most promising focus area - you may need to take out the panel and inspect the rear if the front all looks OK.
Alan

BRB-83-911SC

Maine - I see it now in the WD regarding the T25 line. Interesting. Since Brad was just in the back there changing out the ground strap, could he have disturbed something on the wiper motor causing that T25 circuit to overload and blow #18? Seems plausible. I always like to start where I last was.

dr bob

I happened to notice once how convenient it is to accidentally hit the rear wiper motor area with a ground strap as it gets disconnected from the rear rail. Possible to put full battery potential there by accidentally grounding something like the rear wiper park circuit that is normally powered all the time. Did you make any sparks there while swapping in the new ground strap?

MainePorsche

By looking at the WD re: the wiper motor, the motor appears to be grounded to its housing, and pin 31 takes this to the wiper motor relay completing the ground. When the ground strap was replaced it would do nothing to the motor if disconnected at the battery first and contact was made when the wingnut was removed (obvious). If contact was made between the strap (assuming it's factory) and the motor housing when the wingnut was removed first, it would be 'grounding' a ground. I don't think this would have an impact down the circuit line.
The importance of me saying 'assuming it's (a) factory (ground strap)' has import. If strap is attached to battery the strap can only reach the motor housing when released from the wingnut. It can't reach the input wires to the motor. Being that the wiper function is normal when disconnecting the horn leads me to believe the relay and the motor are unscathed. These motors (wiper, headlight...) are robust. Relays tend to give out first.
Someone like the 'Reverent' Alan can tell you more about the circuitry from fuse 18 and its branch point to the horn relay, and how a defective horn relay can effect T25 current to the motor.
If it were me, I'd swap out a relay for the horn relay, after I investigated the CE board, as my starting point. It's a free $ test.

tilac999

I sure did get a spark. Must have cooked something. I'll look at the rear of the CE panel and swap relays and see if I can get to the bottom of this. One thing I noticed is the #11 fuse for the rear wiper fits loosely now, not like the other fuses. Not making proper contact when tested with circut tester unless wiggling it. Not good.

MainePorsche

If you're going to play at the CE board, you must disconnect the battery.

tilac999

100%.

I got the spark at the negative battery connection when I used a jumper cable to test that my original ground strap was the no-start problem. I must have contacted the rear wiper motor by mistake as that is when the problem began.

MainePorsche

I too have inadvertently made this contact, but I've never lost wiper function. On the 85, I still think it's probably the horn relay, but sounds like your CE board needs a good look at. Best wishes.

Alan

On your '85 fuse 18 feeds the horn and just the parking circuit of the rear wiper motor. Fuse 11 feeds the relay that runs the wiper (and does the 3 wipe extra delay).

There is a protection diode in the motor you could have blown up - in this case if the motor is constantly running the horn should still work it will be when the motor tries to park that the fuse will blow...

You could try removing fuse 18 - get the rear wiper running - insert a good fuse 18 and see if the horn works - until you let the motor park ... pff

If this is the case your motor diode is damaged (short circuit).

You can also replace the rear wiper relay with a standard SPST '53 relay - you won't get the 3 wipes but you will get normal function otherwise. I don't think the relay is your issue but its very easy to try... this will also mask the issue of the diode... so a good test and temp solution perhaps (with an SPST - an SPDT relay will likely still exhibit the issue).

Alan

dr bob

Once you've unfastened the CE panel, you can remove individual wire connectors from the rear panel and give them a gentle squeeze to restore their like-new tension.

If I were hunting this down, I'd start with removing the connections at the wiper motor, and lifting the CE panel connector so the wiring is isolated at both ends. Then test the wiper motor wiring to ground and for continuity, in case a conductor is melted.

tilac999

I've got a '53' relay coming and will swap it out and report back. Thanks.