Tach only works with key

[duhn]

I have an 86 merc 150 hp blackmax. The tachometer works when the key is turning the engine. As soon as you let go of the key when the motor is running, the tach doesn't work.

Any suggestions?

 

[j_martin]

Re: Tach only works with key

Key switch is bad. I'd bet everything else that runs off the 12 volt switched circuit (like dash voltmeter) is also dead.

hope it helps
John

 

[duhn]

Re: Tach only works with key

I just put a new ingition switch cause the kids lost the keys. The only gauges on the console is the tach, speedo and gas gauge. I don't know if the speedo is working because the boat is still on a trailer. The gas gauge works fine.
The SND wire on the back of the tach is only reading 2 volts with the engine running. According to another post that I read, the rectifier is bad.

 

[j_martin]

Re: Tach only works with key

I just put a new ingition switch cause the kids lost the keys. The only gauges on the console is the tach, speedo and gas gauge. I don't know if the speedo is working because the boat is still on a trailer. The gas gauge works fine.
The SND wire on the back of the tach is only reading 2 volts with the engine running. According to another post that I read, the rectifier is bad.

The signal to the tach is one side of the power coil in the stator. It is a wretched AC signal with a DC bias to it. Metering it is pretty useless, unless you use a blocking capacitor and a DVA.

Do you have 12 volt power to the tach when the key is on?. If not, it's in the key switch wiring, and if you do, next item is to check the rectifier. There's a procedure in the FAQ forum here.

hope it helps
John

 

[duhn]

Re: Tach only works with key

There is 12 volts to the tach with the key. I checked the rectifier, it turned out bad. I put a new one in and I still have the same problem.

 

[Barnacle_Bill]

Re: Tach only works with key

You need 3 wires for it to work. (4 if you want it illuminated). Black wire to ground. Tach power goes to the purple wire on the switch, and a gray wire from the harness is the tach signal. There may be a socket on the front of the remote for these connections.