Crazy Ground - power issue on 115ETL77S (1977 - 115 johnson)

[dacostadesigns]

I have been in the process of attaching a tach to my motor. I haven't bee able to get a legible reading on the multi-meter. When I touch the ground/black lead (only) to the ground on the motor gives an un-readible readout. It almost looks like it jumps around based on engine pulses, but this is with ONLY the negative lead touching on the meter. Anybody have thoughts or experience with this?

 

[GA_Boater]

The red lead is dangling? What scale are you using? What happens if the red lead is touched to whatever you are trying to measure?

I would try another meter.

 

[racerone]

The tachometer runs off the alternator / battery charging system.

 

[fireman57]

If it is on a pontoon check all your wires from you battery underneath as mine had a wire pinched where it ran over the crossbraces and was shorting things out.