FAQ Project.

BOSCH WIPER MOTOR RETROFIT by James Seabolt updated 05/30/05

Since day one, the first thing I noticed about my Spider was it's medicore windshield wipers. I tried several things to boost the speed of the wipers. Everything from fixing the ground, cleaning/ greasing the motor, linkages, etc. All of this helped but it still wasn't up to par. I finally came to the conclusion that the problem was the motor itself. This whole system was marginal to begin with and age only makes it worse. But thanks to Ebay I was able to window shop for a new motor that would bolt right in. Finally I found that motor. The motor I used came from a 1977 VW Rabbit. I got this particular motor for $9.00 plus shipping. If you decide to look for one of these motors, any motor from a mid 70s VW or Audi up until the mid 80s should work. Just be sure it uses five wires. Also this wiper motor uses a relay style connector so it was easy to wire up. This motor is made by Bosch and bolts right in. However requires a slight modification so that the wipers will park and allows the use of the intermittant wiper function. This isn't the only motor that will work but seems to be the most readily available and without much fuss to modify.

I was also able to modify a wiper motor from a Yugo which also works much better than the Marelli motor. But after some bench testing I determined the Bosch motor was the best choice. The original speed of the Marelli motor was 46 RPMs on fast. After cleaning the Bosch motor and greasing the commutator bearing and reduction gear I got 73 RPMs when bench tested! Actual speed on a wet windshield was timed at around 65 RPMs. A significant increase in speed. Also the wipers no longer drag across the windshield when trying to swipe the windshield of dew in the morning or mist.

If you haven't checked out my webpage on restoring your electrical system, do so now. I'd also recommend cleaning the wiper linkage to make sure there is no resistance in the system.

Before doing anything, it's best to dismantle the motor, inspect it, give it a good cleaning and repack the reduction gear with grease. I cleaned mine in kerosene but this may not be a good idea on the commutator (the piece with the copper windings) because this is coated with varnish. This varnish protects the windings from shorting out. I'd recommend using an electric motor cleaner available from Autozone. The rest of the parts can be cleaned with kerosene. I used high temperature wheel bearing grease for disc brakes. Once again it might be better to use some sort of grease especially for electric motors. But don't ask me where to get it. I also applied grease to the commutator bearing.

While you have the motor apart, inspect the brushes and the copper portion of the commutator. If anything looks excessively worn, get another motor. They are cheap and not worth rebuilding. If they can be rebuilt.

The easiest way to put the motor back together is to pull the brushes apart and insert the commutator into the gear head. Then stick a flathead screwdriver between the reduction gear and the screw. This will prevent the magnets in the housing from pulling the commutator out of the brushes.

The Bosch motor uses five wires. The 1979+ Spider uses six wires. I believe the 1979+ X 1/9s also use six wires. I wish I had more information to back up my claims but I think Fiats from 1978 and back use five wire wiper motors. Somehow I accumulated several Marelli wiper motors over the years and I have some that use only five wires. So no matter which model or year Fiat you have, you can make this motor work on your car. The trick is to figure out which wires do what on the harness and go from there. Other than my Yugo which uses five wires, the only Fiat I own is a 1980 Spider so this is what I'll concentrate on. If you own say a 1981 X 1/9, these wires should have the same function but are different colors.

Blue/Black --> Always hot when ignition switch is on
Blue/White --> Hot only when wipers are in constant mode
Black/Grey --> Hot on both slow and fast, constant and intermittant
Blue --> Hot only on fast speed
Grey --> Hot only on slow speed
Black --> Ground


Here's a photo of the Yugo motor with the gear exposed. The Bosch motor is similiar.



Notice the fingers on the gear cover. As the motor turns each finger makes contact with a certain spot on the disc. One makes contact all the time. One touches the brass portion of the disc briefly and the other one makes contact most of the time.

The trick was to isolate the finger that is grounded to the body and solder a six wire to it. I took a some wire cutters and cut the tab and bent it so that it did not touch any of the other wires or the body of the wiper motor. Also notice that I trimmed off a section of the motor which was used as a support bracket for the VW wiper linkage. When I linked the wires from the car's wiring harness to the wiper motor, I used 12 AWG wire. This may be overkill. Just don't use anything thinner than 14 AWG.



The color of the wires on the Bosch motor do not correspond like one would expect.

Brown ---> Ground
Red ---> Slow
Yellow ---> Fast
White ----> Hot on fast and slow
Black ---->Always hot
Tab -----> Grounded to the wiper motor's body


Once the tab on the Bosch motor is isolated from the gear cover and a six wire soldered to it, it's just a matter of connecting the wires from the motor to the harness on the Spider.

So it's like this (Bosch motor ---> Spider's harness):

Brown --> Black
Red --> Grey
Yellow -> Blue
White --> Grey Black
Black --> Blue/Black
Tab ---> Blue white

Keep in mind the Spider uses a knob on the dashboard to control the speed so I may have the "speed" wires reversed. You will never know this on a Spider but on the X 1/9 where the speed is selected by the column switch, may show up as being reversed so keep that in mind if this happens.

Now let's assume you have an older Fiat that uses a wiper motor with five wires. Well your in luck because you shouldn't have to isolate the tab from the wiper motor! When I removed the gear cover from a five wire Marelli motor I discovered that one of the contacts in the park mechanism is grounded.

Here is a photo of the Marelli motor's gear cover removed. These should be the same on all Fiats except for the number of wires used. On five wire motors, one of the contacts will be grounded. So there is no need to break the tab on the back of the Bosch motor and solder an extra wire.

Notice that one contact is fixed and is attached to a tab which can make contact with two other contacts depending upon the position of the wiper motor. In this position the circuit is being completed "most" of the time. As the cam gear rotates, it breaks contact and makes contact "breifly" with the other contact. On the backside of the gear cover are wires soldered to these contacts. So once you figure out what these wires do on your Fiat, correspond them to the wires on the Bosch motor.

Since the wiring differs between models throughout the years I cannot explain which wires goto what on every model. But if you wish to carry out this conversion, just send me an email and I'll try to help. I hope this webpage makes sense.

OH and one more thing to mention. The Bosch motor turns in the opposite direction as the Marelli motor. At first I thought this might be an issue but it makes no difference. Just make sure you mark the location on the linkage so the wipers are correctly positioned. I found it best to turn the wiper motor on before connecting it to the linkage so it can park correctly, then connect it to the linkage, turn it on again, then install the wiper arms.