Tach stops when panel lights are switched on

[Chris_Masucci]

Hi Folks,

I recently converted to negative ground and added an alternator. I reversed the loop on the tach and swapped the diode around and it works just fine, including the red charge light. That is until I switch on the panel lights. As soon as I switch the lights on, the tach needle drops to zero. I don't actually have any of the exterior lights hooked up yet, but all the wires are taped off. The gauge lights all come on as expected.

Anyone ever run into something like this before?

Thanks!

 

[Patrick67BJ8]

Hi Folks,

I recently converted to negative ground and added an alternator. I reversed the loop on the tach and swapped the diode around and it works just fine, including the red charge light. That is until I switch on the panel lights. As soon as I switch the lights on, the tach needle drops to zero. I don't actually have any of the exterior lights hooked up yet, but all the wires are taped off. The gauge lights all come on as expected.

Anyone ever run into something like this before?

Thanks!

I made the same conversion and didn't have any problems. Unplug the light assembly that's on the Tach and see if that takes care of it. Also ck the red/white wire to see if it's touching the white wire to the Tach.

 

[Chris_Masucci]

Thanks, I'll check those things. I never considered the current for the light bulb inducing a current on the tach loop, but I bet that would screw things up.

 

[rjc157]

make sure the ground is ok

 

[GregW]

For reference, here is how my tach as wired up.

 

[Patrick67BJ8]

For reference, here is how my tach as wired up.

Try making a smaller loop. Move the ground wire away from the loop and make sure where the ground wire goes the other end is solidly grounded. Check all the grounds on all the instruments.