Help with tach wiring

[marksa1458]

Have a 1968 Mercury 500 with a MercControl controller and would like to connect a tach. the controller has the three plug connector and I purchased the harness off of ebay.

There is a gray and black wire coming off the tach and a brown, black and white coming off the harness.

I think the gray from the tach connects to the brown of the harness for the "send", the black from the tach connects to the black of the harness and I have no clue what the white wire would connect to. Believe it is a hot 12 volt connection and it has a bell shaped plastic connector?

If someone can point me in the right direction it would be appreciated!!!

 

[Faztbullet]

Re: Help with tach wiring

That looks like a old aqua meter tach, you are correct as how the wiring connects and the " bell shape" connector is a lamp socket for that snaps in a guage..

 

[marksa1458]

Re: Help with tach wiring

Great fast reply - Yup it is an Aqua Meter tach - a little rough but like the looks of it.

ok - so it would be ok to tape off the white wire and not use it and the tach should work. Also should it be set to 6P for a mercury engine?

 

[Faztbullet]

Re: Help with tach wiring

Yes tape it off and will have to look up tach setting as if i remember that is driven off switchbox and not the rectifier on that model...

 

[marksa1458]

Re: Help with tach wiring

Connected everything and the engine won't start. Unplug the tach harness and the engine fires right up. After researching some more, some posts said a wire had to be disconnected and reconnected to the rectifier. If this is the case what wire has to be disconnected and where do I connect it to? Or is the tach bad?

 

[Faztbullet]

Re: Help with tach wiring

I looked up wiring diagram and whats happening is with tach installed its grounding the switchbox. The diagram shows wiring is jumped on rear of harness(engine) and this would have to go to one side of the rectifier to make tach work.
http://www.maxrules.com/oldmercs/Wiring/1966ona/26A.jpg

 

[marksa1458]

Re: Help with tach wiring

Looks like the wire harness at the engine didn't have a connection for the tach. I couldn't get continuity at any of the pins and the 3 pin connector on the remote.

Ended up running two wires - one connected to the rectifier and the other connected to the ground at the starter, set the guage to 4 pulses and it works.

Will keeping the guague connected this way damage the rectifier or interfere with the charging system?