355 Headlight weirdness

Hey all, I'm quite flummoxed by my left headlight motor's behavior. When I got the car, it was "trying" to operate, and would move a little bit down if I manually put it up. I took it apart, cleaned it up, and bench tested it (once the wiring diagram clued me in to what each of the five wires do), and it seems fine. But it doesn't turn when reinstalled, and my multimeter is getting very strange readings from the car after I removed the cleaned-up motor. When measuring between ground and the wire that tells the motor to operate, I'm getting fluctuating voltage, bouncing rapidly among 0, 7.5, and 68.5! The other four wires all read zero relative to ground. When I switch the position of the headlights, the behavior moves to the other signal wire. (One is green with a black stripe, one is purple.) I've tried swapping the relays and inspecting the fuse, and no matter what, I get good behavior on the right headlight and bad on the left headlight. The 68.5 volt reading has me thinking I somehow fried whatever the "headlight controller" is. (I would never think such a thing existed, but there's relay for it.)

Anyone seen this before?

 

Oops, I think the weird voltage is user error. I got the same results testing the terminals on the battery of my other car. Which implies that my motor is still malfunctioning for some reason. I'll just slink away now...

 

What are the diodes for? I mean, I know what diodes do in general, but why are there some inside the goo on this motor?

I only swapped relays, not headlights or motors. I didn't understand the fusebox legend, and thought there was some kind of separate "controller." It doesn't make sense, but I don't think a third relay truly makes sense either. It seems a small switch could handle enough current to drive two relays in parallel. To add to my confusion, I was using my new meter incorrectly, so I thought I was getting high-voltage transients from a damaged electronic device of some kind. Turns out the meter defaults to AC mode. Suboptimal for my purposes.

Further examination shows I didn't clean up the disc on the motor's gear well enough. I used 400 grit sandpaper, but there is still corrosion, which doesn't conduct electricity. (I thought it was just discoloration.) Continuity checks confirm major dead spots remain. So I ordered a drill bit with a grinding stone on it. I suspect I will have both headlights operational again late tomorrow night!

 

Wow, thanks for this - it's much better than the one in the shop manual, which doesn't show the diodes, is not at all clear about what/where the plugs are, and worse, has different colors from the ones on the motor itself. Did you make this one? Or is there a better source than the shop manual?

 

Finally got the motor fixed! The first shot shows part of the switch with several areas rendered nonconductive by corrosion. It had actually been worse, before I sanded it with 400 grit paper. At that point, it had started closing all the way, but not opening. So I took it back apart and spent several minutes grinding it with a stone in my drill, being careful to avoid the plastic bumps (which are surprisingly hard to see in my office light), and finally reaching the state in the second picture. Since this one showed continuity on all spots on the disc, I put it back together, even though it still looks ugly and not shiny. The point is, it works now!
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Yeah, I wanted to make sure I didn't overpay for a 355, plus I really love the color scheme on mine (Grigio Titanio with rosso something interior). Because of that, I bought one with a long list of issues. I don't mind this at all, as it builds familiarity with the car, and I'm a fan of sweat equity. As for the magnitude of this particular issue, given the amount of liquid that ran out of this motor when I first disassembled it, it had obviously been operated or stored in the rain quite a lot. I just hope there's not comparable neglect/abuse damage to the engine.

 

I think you were either the author or the inspiration for the pdf I used to tell me how to deal with this issue, so thanks for that!