1978 85HP, Johnson Power Tilt and Trim

I have a 1978, 85 HP Johnson outboard. I have rebuilt the boat and I have installed a trim gauge. The old boat didn't have 1. I have tested the sending unit with an Ohms meter and the gauge. Both work as they should. My gauge has 3 terminals on it other than the lighting. one has an (I) on it. I would assume this would be the "Hot" or 12V when the ignition switch is turned on. Another one has an (S) on it. I assume this one would be from the sending unit. And the last is in the middle and I assume it to be ground. When I power up the system the gauge will not function as it should. it will not register untill the engine gets to almost full tilt then the gauge will jump to reading full tilt. I assume I have it wired wrong and have changed it around but I still can't get it to work. I would thank you for any help as how to route the wiring. I have 2 wires coming from the sending unit. both look to be black. Thanks :'(

Re: 1978 85HP, Johnson Power Tilt and Trim

Right on the terminals. It needs two connections on the ground terminal. The second wire from the trim sender is one and a ground is the other.

Re: 1978 85HP, Johnson Power Tilt and Trim

Thanks for the info I'll give it a try.d

Re: 1978 85HP, Johnson Power Tilt and Trim

Cray3194 said:

Thanks for the info I'll give it a try.d

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I retraced my wiring and testing. I found that I did indeed have a bad sending unit. So I bought a new one but my gauge reads it all backwards. I have change the leads around from the sending unit thinking I could reverse the current flow. No such luck for me. The gauge reads DN when the motor is UP and UP when the motor is DN. Any clues? :/