Tachometer...only 2 wires?

[rtpassini]

Im replacing the factory tach and theres only two wires going to it. blackish/grey and green.

my new tach has sending unit, ground, and ignition hookups (along with lights)

do i need to run another wire?

 

[Moody Blue]

Re: Tachometer...only 2 wires?

I installed a tach for that same motor last summer. There is only 1 wire needed from the motor. You need to take the tach signal from either side of the rectifier inputs from the stator (yellow wires). The old style tachs took the signal from the brown terminal on the switchbox but this will no longer work with the new style tachs.

The other connections you need is switched +12V, GND and a power source for the back lighting if you so desire. Depending on the type of control box you have, there should be a tach connection plug somewhere on it. My "MercControl" box has a 3 pin connector that provides the tach signal from the motor (see above regarding where to pick off the signal), switched +12 and GND. You can pick up the tach harness on ebay if you search. The tach harness plugs into the control box and runs to the tach with all necessary wires (except for back lighting).

 

[rtpassini]

Re: Tachometer...only 2 wires?

can i just take the brown wire from the switch box and tap it into the rectifier wire? or do i need to leave the brown wire connected to the switchbox.

and when you say switched 12 volt, what do you mean by switched?

 

[Barnacle_Bill]

Re: Tachometer...only 2 wires?

Switched means you get power from the ignition switch. Normally a purple wire.

 

[Chris1956]

Re: Tachometer...only 2 wires?

RT, You need to see where the brown wire is connected under the cowling. On those old motors, some of the tachs ran off the switchbox. The newer tach run off the stator. Find the rectifier. Your's should be a big red one in the lower cowling. Move the brown wire from the switchbox to one of the rectifier's yellow wires. Do not move the brown wire that goes to the distributor.

The MerControl should have a three prong connector on it's front. That connector has switched +12VDC, ground and tach signal.

 

[rtpassini]

Re: Tachometer...only 2 wires?

when i was rewiring the motor, there was a brown wire that went from the connector to the switchbox for the tach. my rectifier is black. ill just add it to one side. or can i leave it and just use a jumper wire that goes from the rectifier to the brown wire on the switchbox....

i just dont want to fry anything with my motor or electronics, so i just want to be clear.

 

[Moody Blue]

Re: Tachometer...only 2 wires?

Your reply is a little unclear. Do not jumper anything together.

On the side of the switchbox with 4 wires, remove the brown wire from the switchbox terminal and connect it to one side (either one) of the rectifier.

That brown wire runs in the factory harness back to the control box (Mercontrol?) and goes directly to the 3 pin tach connector on the front edge. That tach connector also provides the switched +12V and GND needed to complete the connections to your tach.

The tach will have the following terminals (or similar) on the back;

IGN - connect to switched +12V
S(ignal) - connect to tach signal
GND - connect to system ground

Good luck.

 

[rtpassini]

Re: Tachometer...only 2 wires?

thanks, thats what i was looking for! yes its a mercontrol.

i wasnt sure if leaving an empty spot on the switch box was okay or not.

 

[rtpassini]

Re: Tachometer...only 2 wires?

old thread bringing back. now that i have the motor running, i cant get the tach to work

i have three wires from the control box. black, green, and white.
i cant seem to get the tach to work no matter how i put them. even the back light wont work. although, that could be a different issue.

also, what setting should i have the tach setting on? the little dial on back that you turn with a screwdriver.

 

[rtpassini]

Re: Tachometer...only 2 wires?

i think its supposed to be on 6p? is that correct. but i still could find anything about the color wires i have...

 

[Barnacle_Bill]

Re: Tachometer...only 2 wires?

Green wire? The ones you should be using are black, white and brown (sender). 6P is correct.

 

[rtpassini]

Re: Tachometer...only 2 wires?

yeah. its green. i have also heard of a purple wire being used...
and no, im not color blind. haha.

but my harness is white, black, and green.

the 2 used before i hooked up the new tach was black (im assuming ground) and green. is that the signal? would white be ignition?

 

[Moody Blue]

Re: Tachometer...only 2 wires?

OK, 3 wires from the control box "tach connector" should be as follows;
BLACK = GND
WHITE = switched +12V (ignition)
BROWN (green ?) = tach signal

On the tach you should have 5 terminals;
S = sender = tach signal
I = ignition = switched +12V
Gnd = GND
There are also two terminals for the back light, a +12V and GND. Don't power the backlight bulb from the ignition signal.

Set the selector switch to 12P. Use a multimeter and verify +12V on the white wire with the key in RUN position. Perform a continuity check for both the GND wire and the tach signal wire back to the motor.

 

[rtpassini]

Re: Tachometer...only 2 wires?

at the tach i tested for 12 volts with it in run.

the GREEN (or brown) tested at -12 volts.
the WHITE wire tested at .225 or something like that.

whats this mean?