Tach wont work

[mdrussell2]

hey guy I have a 73 sleekcraft and a 75 merc inline 150hp motor. I bought a new tach from autozone and cant get it to work. I tried hooking it up as to manufacturers specs but i get power but with boat on I get no rpms. I also tried a couple places on the switch box the motor manual says is where the tach wire goes to and no luck. the manf. spec says took hook up green wire to negitive side of coil but my coil is hot on both sides. kinda stumped here. Can i not use an automotive tach for marine use?

 

[Moody Blue]

Re: Tach wont work

If you bought an automotive tach then you are out of luck. Not compatible with the marine ignition systems.

When you do find a marine tach, you may need to change the tach pick-up point on the motor. Originally the tach signal (brown wire) was taken from the BROWN terminal on the switchbox. The newer tachs (1980's ish) require the tach signal to be taken off the stator directly. You will have to remove the BROWN tach signal wire from the switchbox and connect it to either of the YELLOW wires that connect to the rectifier. These yellow wires are the stator wires.

 

[mdrussell2]

Re: Tach wont work

after looking in the motor manual i saw that there is a tach hook up on the ignition control box if i used it would i still have to change the brown wire to the stator

 

[Silvertip]

Re: Tach wont work

No -- you can't use an auto tach on an outboard. Outboard tachs get their signal from the charging system (the stator). Auto tachs get their signals from the ignition system. These are two totally different looking pulses. The auto tach cannot recognize the output pulses (or count them properly if it did).

 

[mdrussell2]

Re: Tach wont work

sorry i was talking about with an outboad tach not the auto tach trying to figure out if i have to change tach signal from the switchbox to the stator if i use the control box hook up or does it still depend on the year of the tach

 

[Moody Blue]

Re: Tach wont work

The tach connector on the MerControl control box is wired back to the motor thru the wiring harness. The tach signal source, is still at the engine. If the brown wire is connected to the switchbox, you will have to remove it and connect it to one of the yellow wires on the rectifier. Does not matter which yellow wire. If you have a tach from the 60's or early 70's then leave the brown wire connected to the switchbox.

 

[mdrussell2]

Re: Tach wont work

thanx for the help guys