Blower motor wiring short

[rkohl44]

I had an intermittent short in my blower motor wiring that I finally resolved. Sometimes the blower would work, sometimes not, sometimes if I jiggled the throttle, the motor would come on. Often, when I moved the throttle, the blower motor would rev up or down. Turns out, the ground wire ran all the way to the throttle cable clamp just aft of the carburetor. That connection had become quite corroded and flaky. To fix it, I simply cut the ground wire and made a new connection to one of the instrument panel grounds. The new connection is about 18 inches versus a 10 foot run to the throttle clamp.

Q1: Why (this is a Catalina 30) did the blower ground run 10 feet to the throttle cable clamp, when a much shorter connection was available?

Q2: Is there a reason why I should NOT run the blower motor ground to the instrument panel?

[ndutton]

In a nutshell, builders do things the way they do for their convenience, not yours.

All of the wiring connected between the instrument panel and engine is in a single harness often originally connected by plugs at either end. Mr. installer cuts a square hole for the panel, plugs in the harness and screws the panel in place. DONE in a matter of minutes! The engine end is often the same, prewired with a plug. With the blower switch on the instrument panel, its wiring is included in the factory harness that goes to the engine therefore that's where the blower wiring was originally connected.

Addressing your second question, there is an electrical engineering advantage beyond production line convenience though. When current flows through a single wire a magnetic field is created around the wire, known as a Gauss Field. That magnetic field can create havoc with sensitive devices and on a boat the compass is particularly vulnerable. Running both wires of a circuit together its entire length, both wires develop their own Gauss Fields, equal and opposite thereby cancelling each other out. Twisting the wires is even better.

As reported, your issue was with the connections, not the length so it's my opinion you are better off with the long-ish ground wire run from the blower back to the engine in immediate proximity with the positive load wire.

[rkohl44]

Thanks for the explanation and understood.

For whatever reason, the positive lead on my blower was connected to a positive terminal on the instrument panel already. The ground was the only one running back (err...forward) to the engine. I'll twist them together next time I'm aboard for some Gauss cancellation.

Also, my boat doesn't have the plugs. It has a thick bundle of wires from the engine to the panel. There's even a white 10 (maybe 12) gauge wire that's not connected to anything.

[sastanley]

What year is your C-30? Sounds like someone may have already re-wired it? My '77, which I know was still wired stock from CA, had the blower wires to the instrument panel. I am thinking about changing that to take the load off the instrument panel, as I have some extra circuits on my DC panel. I even have a new blower motor to put in, so I might as well fix the wiring too. On my boat, that thing draws 4.5 amps!

[rkohl44]

1982 and it doesn't look like it has ever been rewired, at least not in recent history!