Friday, January 11, 2008


Wiper Motor Wiring, 1/6/2008

We had a beautiful day on Sunday, temps in the 50's, so I got a little work done on the boat.

The shrink wrap zipper door arrived Friday, so I put that on to gain access to the inside of the boat. Piece of cake -- tape it on, unzip, cut a hole in the shrink wrap. The inside of the boat seemed in fine shape, no condensation or mildew problems.

I went to work immediately on the windshield wiper situation. Over the summer, I bought replacement motors which appear identical to the old motors, but when I connected them up, they didn't turn on. I bench tested them with a 12-volt battery, and they work fine like that, so I knew it was a wiring problem on the boat. Both the old and new motors have an identical set of connections:
  1. "s": switched wire, runs to the switch at the helm
  2. "-": the ground wire
  3. "+": always-on wire, so the motor can self-park after the switch is turned off
Simple, yet the new motors didn't work. Some investigating with a multimeter revealed the problem: in the original wiring, the "s" connection ran through a switch to the ground, rather than to the positive feed. Sure enough, the owner's manual has it diagrammed exactly that way. I'm not an electrician, so I don't really understand why it would be wired that way.

No matter, I just rewired according to the instructions with the new motor. It was a fairly straightforward change: reroute the wire from the switched terminal to the positive feed instead of the ground bus. Now the positive feed comes off the fuse panel and splits to the "s" and "+" terminals, and the ground wire simply runs directly from the ground bus to the "-" terminal. I attempted a Visio diagram (below) of the change, so I can update the owner's manual to show the new configuration.

I attached one of the new motors, and it now works exactly like it should. In the spring, when I can access the bow of the boat again (under shrinkwrap now), I'll finish installing the motors in the windshield frame.

Thursday, January 3, 2008

Corrosion Protection

Oops, forgot one:
  • Galvanic Isolator. When the boat is connected to shore power (as ours always is), stray current flows through the AC ground and the DC bonding system. This current can really cause the zinc anodes to dissolve away quickly. An isolator blocks low voltage in the green AC ground wire, but passes higher voltages through if there's an electrical fault.