Mystery wire on alternator

Dec 4, 2019
25
Beneteau 423 Jacksonville
Now that I have your attention, there really is a mystery wire on the alternator. On my Volvo Penta D2 55, there is a red 12 gauge wire attached to the "D+" terminal on the alternator. There are also 2 wires on a spade connector there (one red/blue, one brown) that go into the big relay thingy on the port side of the motor. The red wire, which looks aftermarket, goes to a relay in the aft cabin (2-cabin model here) that appears to do nothing. The red wire attaches to the relay, and there are 2 black wires Siamesed and go to battery ground, I am pretty sure. There are no other wires on the relay. There are disconnected/cut off wires labeled "autopilot" in the area, but they are clearly not in use.
When the ignition key is off, the red wire has no voltage. When it is on, there is about 3.5 volts in the wire, and when running, the wire/stud shows system voltage - 13 volts or so. From my info search on the engine wiring, the two other wires go to the engine panel and input to the low voltage light. My feeble electrical knowledge says this is to excite the field of the alternator at low RPM.
Any ideas? I am planning to replace the alternator and want to make sure I don't remove/disconnect anything really important.
 
Dec 4, 2019
25
Beneteau 423 Jacksonville
Further investigation reveals that the mystery wire leads to a relay for the windlass. Said relay is inoperative. We were guessing that it was there so the engine had to be running to use the windlass. The system was replaced and rewired sometime and the above was bypassed.
 

NYSail

.
Jan 6, 2006
3,048
Beneteau 423 Mt. Sinai, NY
Yep.... beneteau wired the windlass that’m way. I am going to also remove mine.wher did you find the relay?

greg
 
Dec 4, 2019
25
Beneteau 423 Jacksonville
I followed the red wire off the alternator under the port aft cabin bunk, (we have a 2 cabin model) in the space where the battery wires live. There is another relay for the windlass, not connected to the alternator, and the relay in question is outboard of that device. I disconnected the relay from the alternator and the ground to the battery. There is another wire, a black one, that disappears into the wrist-sized wiring bundle aft of the engine, along with the old autopilot wires, also cut off and coiled up.
Working on an older boat (and even new boats) requires you to be part mechanic, part plumber, part electrician, and a large part detective.
 
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Oct 22, 2014
20,991
CAL 35 Cruiser #21 moored EVERETT WA
Working on an older boat (and even new boats) requires you to be part mechanic, part plumber, part electrician, and a large part detective.
It is in the nature of boats and the job description of the owner.

Thinking on a grander scale, as Skipper at sea, you are the mayor, police chief, public works engineer, diplomat, and minister. And while holding all of these titles your are expected to know and preform all of the tasks for their department staffs.

Sometimes it is great sailing a boat solo. I can ignore the complaints.
 
Dec 4, 2019
25
Beneteau 423 Jacksonville
And the skipper must do this in heavy seas, at night, by the light of a headlamp. But it gives us a knowledge of the boat and all those other things that benefits us at times.

As for sailing alone, single seat military pilots have said they enjoy the quality of the company in the cockpit...
 
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SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Where do you sail out of in, Jacksonville, Jeff?
 
Dec 4, 2019
25
Beneteau 423 Jacksonville
The Riverside area. The St Johns River is a nearly 40 mile long, 3 mile wide sailor‘s dream. We are several hours from the ocean, and the tidal currents can add to that trip. Once there you have easy day sails to St Augustine and Cumberland Island. I guess I should note that I live in Jacksonville, Fl