View Full Version : Question about trim sending unit

01-21-2012, 12:49 PM
Does anyone know if a trim sending unit would be destroyed if +12V was applied to it instead of being connected to the sending connection on the trim gauge? I can't read any resistance on the brand new sending unit after I accidently applied +12V to the new one on my 23' Donzi fishing boat with a 250HP Merc outboard. I am installing a trim gauge which the boat never had before, but I reconnected the wiring the same way as when I tore it down without realizing the brown with white tracer wire was the sending unit wire which used to be connected to the ignition post for some unknown reason. It would not have mattered before since there was no sending unit. Bill

01-21-2012, 03:05 PM
Bill, I don't know very much about outboards, but the sending unit on an outdrive is a potentiometer. Ultimately the signal comes from the gauge and grounds through the pot and is read in Ohms.
If similar, to outboards, you may have fried it.

01-21-2012, 04:13 PM
I would guess fried. Put an ohm meter across it and turn it up and down.
The reading should vary with the turning and not be zero until all the way to one end.

Most likely will be shorted or open at part of the travel if cooked.

01-21-2012, 08:53 PM
Thank you. Yes, I assumed it is ruined since I get an open circuit from the sending wire to ground (the sending unit has a ground wire). That was a $48 mistake that I should have caught before hooking up the sending wire the way it was when I bought the boat. Bill

01-26-2012, 02:24 PM
I finally got the trim gauge working late last night, but not without quite a bit of adjustments - :yes: