Installed a new Autometer tach. At idle the RPMs jump when the turn signal is engaged. Any ideas on what could be causing this? Grounds are solid and wiring is all correct.

 

Where are you connected to power for the tach?

 

Switched battery power from the fuse block. My oil pressure, water temp and voltage gauges are also using the same feed.

 

The tach light feed is tapped off the speedo gauge light wire. I believe its the grey one

 

Gray lights are instrument panel lights and that should not matter. For starters you might try hooking a jumper directly to the power at the battery and see if that helps. Electrical issues can be strange and hard to find.

 

Yes they can be. I will try your suggestion.

Thanks

 

Sounds right and matches the installation diagram I found on the web:



What type of ignition system do you have?

 

What type of ignition system do you have?[/QUOTE]

GM HEI

 

The only thing I can think of to cause that is the voltage at the switched power source is dipping when the turn signal bulbs illuminate. A regular (low) current alternator and minimum output at idle speed may be the cause. What is your voltage gauge doing when this happens?

 

Also double check your ground connection and make sure all your crimp terminals are solid. You can try tapping off a different power point.

 

Rick -a couple of thoughts.

1) Where did you end up mounting your tac?

2) Pull the top of your cap off and shock your coil wires to make sure they are not loose.

3) Back in the day, I had a Sun tac mounted in my 72 CS with HEI, and I could have sworn there was a switch or stew that allowed you to go from points to electronic ignition. I never had a problem with it. However I have been reading about needing a resistor in the line for certain tacs. I would say this is a last resort, but here is an example of what I am talking about .

 

Thanks guys for the comments. I'll be working on this at some point this week and will report back.....