Tachometer is dead

[trcop]

I traced the wires at the gauge and found that it had 12 volt at the ignition connection and also twelve volts at the signal connection...(grey wire) however when i start the engine and disconnect the grey wire clip off the motor the engine stalls.....there is a purple wire in the two wire harness but that also is has a 12 volt reading with the test light.... i also jumped the signal and ground connection behind the gauge and the needle did not move....

MY question is how do i determine if the gauge OR if the sending unit is bad...im pretty handy but find this whole electrical system is somewhat of a puzzle...

i have faria guages and am running a fourwinns 4 cyclinder horizon 170 volvo penta 3.0GLP-C.....

please help...and thank you for your effort and time.

 

[Bondo]

I traced the wires at the gauge and found that it had 12 volt at the ignition connection and also twelve volts at the signal connection...(grey wire) however when i start the engine and disconnect the grey wire clip off the motor the engine stalls.....there is a purple wire in the two wire harness but that also is has a 12 volt reading with the test light.... i also jumped the signal and ground connection behind the gauge and the needle did not move....

MY question is how do i determine if the gauge OR if the sending unit is bad...im pretty handy but find this whole electrical system is somewhat of a puzzle...

i have faria guages and am running a fourwinns 4 cyclinder horizon 170 volvo penta 3.0GLP-C.....

please help...and thank you for your effort and time.

Ayuh,.... The sender unit is the Coil,.... it's (-) terminal,.....

If ya ground the grey wire the motor dies, the Coil is grounded,...
The purple feeds the Coil,...

 

[trcop]

im sorry, i think i confused two separate issues(also not sure if what i did was correct so here it goes)....first my question should be how do i know if the coil is bad.....what is the proper testing procedure for the coil and SECONDLY how should i test the gauge itself?