Tachometer hookup on a 1978 305 OMC

[fabrimacator21]

When I bought my boat the tach wasn't working... after some inspection something doesn't seem quite right with the wiring.

First off I'm not sure what I'm looking at. Theres the coil, then theres a black box looking thing bolted to a bracked on the intake manifold and it has a few wires running to the coil. Is this the ignition module? The black box has a green wire sticking out that got cut and I have no idea where it should go. I'm guessing to the coil or tach. Can this be right? I don't have the money for a manual right now... is there anywhere I could get a wiring diagram for it?

Where should the signal come from for the tach? Theres no wires coming off the coil itself, just 2 posts with a bunch of wires hooked up to both.

Also the tach only has 2 posts.... one ground and one signal... should both 12v power and signal be on the signal post?

I'll try to get some pics of it this weekend.

 

[fabrimacator21]

Re: Tachometer hookup on a 1978 305 OMC

Ok.... I bought a new tach and now I'm wondering how to figure out which is + and - on the coil. One side say BAT... is that pausitive?

Also the directions say to hookup the hot wire for the tach to any wire that has 12v signal in the "ON" position.... not accessories. Can hooking it up to a wire that also has power when the accessories are on hurt it?