Early 90's 50hp Yamaha 2-stroke with the proper separate tilt and trim rams.

It's a 3-wire setup, I see +12v on both the up and down wires simultaneously when I hit the trim button in either direction, possibly a short between the 2 windings?

Foxtrot Oscar wrote: Sort-of reads like the switch is faulty - delivering +12v to both Bl & Gr wires. Bypass the switch (Disconnect it or the harness) and using a remote battery or jumper leads apply +12v to one wire/terminal (Bl or Gr) and Earth return the Black wire to the battery -ve post. If the trim motor runs then the problem is the switch. Possibly corrosion internally? Good luck.

Are you getting a solid earth on the earth wire? One way to wire a 3 wire motor would be a single main winding with a centre tap rather than 2 independent windings. That would mean that you would get your +12v on each lead even with only one of them activated. High current windings on a motor like that may only be very low ohmage so not strange to see it as close too a dead short on your average meter. Check your earths.

Tagit wrote: Are you getting a solid earth on the earth wire? One way to wire a 3 wire motor would be a single main winding with a centre tap rather than 2 independent windings. That would mean that you would get your +12v on each lead even with only one of them activated. High current windings on a motor like that may only be very low ohmage so not strange to see it as close too a dead short on your average meter. Check your earths.

Ha, gave the ground wire a wiggle and the wire dropped off the end of the crimp connector. Issue resolved, thanks all :)

Thanks for the followup report. I spent 10 mins yesterday writing you some extra diagnostic ideas but the damn system didn't post due to the dodgy internet I was using and I was too busy to rewrite it. One of the first things on the list was to try and bend the earth wire at the crimp edge and give it a decent tug. A huge % of electrical issues on boats can be traced back to corrosion in the wire where it goes into the terminal lug. Three rally simple tests to try if you don't have a meter handy - 1) heat - does the joint get hot when you try to operate the equipment, 2) Bend - does the wire feel too 'floppy' where it goes into the terminal lug, 3) tug - does the wire pull out when you tug it away from the lug.