Tach Lights not working

[Zonie]

You can use your DVOM to check continuity between the blue on the speedo to the output on the nav switch, and do the same from the black on the speedo to a known good ground. That should pinpoint your problem. If it turns out to be a ground you can just tie into any ground from one of the other lights. Another approach would be to use a test light from the blue on the speedo to one of the grounds on the other lights. Then do the same from the positive (blue) on one of the other lights to the ground on the speedo. Same test, different tools.

 

[arlowe13]

You can use your DVOM to check continuity between the blue on the speedo to the output on the nav switch, and do the same from the black on the speedo to a known good ground. That should pinpoint your problem. If it turns out to be a ground you can just tie into any ground from one of the other lights. Another approach would be to use a test light from the blue on the speedo to one of the grounds on the other lights. Then do the same from the positive (blue) on one of the other lights to the ground on the speedo. Same test, different tools.

Yes, I have already determined the grounds are different for the tachs, only. The ground wire going to the tachs comes from the engine versus the house battery of all the other lights, BUT the positive lead for the tach lights IS coming from the house battery. This is why I think just connecting the negative poles of my 2 batteries might solve this.

 

[arlowe13]

All is good after connecting the negative posts of my two batteries.