Diagnose a wiper problem

[Redline]

Back history: The previous owner of my Coupe had replaced the wiper speed rheostat with a simple pushbutton switch. No idea why. I put in a proper rheostat and all worked fine for three years.

The other week I lost the wipers (in a downpour of course) after it had swept 2 times. Each time I replaced the 8A fuse, it would blow after half a sweep.

I took the linkages out, cleaned and greased them (although to be honest, they were quite free and the grease was still quite clean).

I disconnected the motor from the harness (and noticed at that time the stellar wire substitution job that the PO had done):





Anyway, with the motor disconnected from the wiring harness, if I turned the column switch on, the relay would click on and off under the hood, and I could run the blower motor simultaneously without any problems. No blown fuse. I thought this meant (thankfully) that there were no weird shorts in the dashboard and internal wiring.

I hooked up the motor (without linkages) and it would blow the fuse after only a second or so of running. "Aha!", I thought, the motor is bad. Ordered a new one for a pre-1973 BS Spider.

So first imagine my surprise when I got this (top):



The mounting bosses are the wrong size. Don't tell me Fiat used a different motor for the Coupe and Spider...

I decided anyway to hook it up and see how well a brand new motor runs. Slowly. And it blows the fuse after a second. Grrrr.

Any ideas of what to check and how (i.e. with a multimeter, voltage drop across what parts of the circuit etc.)?

[spider2081]

Couple questions
Do you have a wire diagram for your car
Do you have a way to test the original motor out of the car? If not is there a place you can get it tested.

without being able to test the motor you have no way or really knowing if the problem is in the car or the wiper motor.

I have tested Spider motors that resemble your new motor and they draw less then 5 amps on high speed. I would think you original motor should be about the same.

[Redline]

I have a wiring diagram.
I could probably test the current draw at work.

[spectorbob]

Hey, I'm new to fiats, so someone else will have an idea about common issues, but from an electrical standpoint, you probably have a high resistance, corrosion somewhere. If you suspect rheostat, you can bypass it and then give it a try. The connector you show also looks a little iffy.

[Redline]

Thanks. The rheostat has a normal resistance over its range, but I'll bypass it anyway to see what's up. I poked around the wiring diagram for the first time in ages and was amused at the grounding in the car. Maybe it's the same in all cars, as I've never really looked before at grounds or ground problems, but I was surprised to see how far away some components are grounded through other, unrelated components. The wiper motor, as far as I see, ground all the way back at the headlight relay and the interval wiper rheostat is grounded via the cigarette lighter. It starts to make you appreciate how you can totally ruin the system if you haphazardly cut out circuits when "fixing" things.

The connector is certainly iffy, in terms of splicing in the wire, but the blades are all clean on the five blade connectors and that one single wire has a solid crimp to the loose blade. As far as I can tell, it anchors securely, and as the new motor with a new connector also blows the fuse, I guess it's not that oddball connector that is the problem.

[spider2081]

I could be mistaken but I think the main ground for the wiper motor is the case of the motor itself.

[Redline]

There are some inconsistencies between the nice PDF wiring diagrams that are available on the web and the one that's in my owner's manual, which I tend to favour. It's a Euro-market car, of course, so maybe also different. My diagram certainly shows no direct ground of the motor case, but rather grounding via one of the five wires.

On the US 69-73 Spider wiring diagrams, it shows a 6-wire connector, which is anyway different, and the wiper motor is grounded back to a common ground near the battery.

[spider2081]

I wasn't sure. I know i have run the motor for my 81 spider out of the car by attaching a ground to the metal case. Sounds like you have the ground location under control. A bad ground would not cause a fuse to blow. It could cause the motor to turn slow or not at all but not the fuse to blow. Our cars have been around so long a previous owner could have used the wiper circuit for an added light or horn or whatever. That is why I think checking the motor out of the car is so important. You might find out yu have 2 good wiper motors.

[Redline]

The sharp eyed will noticed that the PO rewired the motor from 5-wire to 4-wire, leaving off the Blue/White wire that comes from both the interval wiper controller and column switch. Why do people do this?



The wiring to the motor seems normal and in good shape*. The dash rheostat gives 0 - 65 ohm over its range. The interval controller clicks on and off normally with power

Any idea what the consequences of this deletion on the motor side would be? With this odd wiring, the interval function still worked before the new problems, so what is the point of the 5th wire on the motor?



* however, the voltage at the connector is only about 11.5 V (12.4 V at battery) with the engine not running (but ignition on). Is this normal?

[spider2081]

Maybe that motor is not the original motor that came with the car. Did you take out the last screw and inspect the park/delay switch on the other side of the soldered connections?
Looking at your photo there is a red and a green wire going into the motor itself. I believe one is the fast and one is the slow speed winding in the motor. The motor ground is made to the motor housing by the remaining screw in the park switch cover.
I would think if the new motor wiring does not match the removed motor wiring it will not work properly. I would compare them. You may have to modify the new motor wiring for it to work properly.

A friend purchased a new wiper motor for his 75 Spider and I had to swap a couple wires on the park/delay switch. I remember one was a ground don't remember what the other was.

[Redline]

Bypassed the rheostat and still no happiness. Still need to test the motor draw on a test bench...

But at least I finally found an accurate wiring diagram for the BC Coupe:

[spider2081]

WoW that is pretty cool. The beauty of schematic diagrams is the symbols are internationally recognized so anyone anywhere in the whole wide world can read them. Great find. LOL

[DocGraphics]

As one who has drawn/read schematics for years that's funny right there, don't matter who you are!

[TX82FIAT]

I'll bite. Maybe poor grounds but I suspect a hot to ground at some point in the circuit prior to the motor. Older wires may have moved or rested against metal.