This question came about while I was trying to fix a VHF transmitting hum. I was disconnecting the radio, and when I pulled the black ground wire off the 12V panel, the radio still would power on. I found that the coax antenna cable was carrying strong DC ground to the radio. Also, I found that with any of the mast lights off, their red positive wires would also read as weak DC negative grounds (10-11.5 V, I'm guessing light contact of exposed wires with the mast). When you flip them on they read as normal positives and the lights operate as normal.
So, I'm guessing I should go up there and insulate around all the light connections (steaming, foredeck, anchor, tricolor) and also insulate the VHF antenna bracket? Anyone else had to track this down before? If our masts are all part of the common ground, seems like a bunch of us would have this going on unless we all had really great previous owners.
Incidentally, this wasn't the source of the radio transmit hum. So, it really isn't causing a problem that I can tell. Leave as is?
_________________ Zach Duncan SV Holiday Hull# 280
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