68-70 B-Body tach from charger specialties ( non rally) issue with tach bouncing

[Suregrip391]

I hooked up a tach in my 70 B-Body I purchased from Charger Specialties. I also purchased the tach lead from them. It's a reproduction of the original. I hooked the one wire to the negative side of the coil and the other to a 12v power "key on" terminal on the back side of my fuse box. The tach works great except for when I use a turn signal. It pulses and gets worse when I use the clutch pedal it seems. Bounces around all crazy. Driving down the road it's nice and smooth. No issues. At first I thought I had it on a turn signal circuit so I moved it to another 12v "key on" terminal and it does the same thing.

I checked with Russ at charger specialties and he said he don't know what is causing this. He said if I have a condenser hooked up to the positive side of the coil, try it without. If I don't have a condenser, put one on! So I tried it both ways, made no difference.

I'm thinking it's a ground issue but I don't know for certain where to start with this. Any ideas?

 

[Bruzilla]

Sounds like a bad grounding issue.

 

[Suregrip391]

Yes, I agree with you there. But not sure where to ground. The tach housing sits in the cluster is made of plastic. I think it gets its ground from a cluster screw but not certain.

 

[Suregrip391]

Fixed! Installed ground strap from firewall to block and cleaned up the ground from battery to core support.

 

[GetX'd]

Congrats! I had a similar issue with a factory tach that was bouncing all over the place too. We got in front of my issue with the ground as well.

 

[Suregrip391]

Congrats! I had a similar issue with a factory tach that was bouncing all over the place too. We got in front of my issue with the ground as well.

Thanks! It's great when you can get things working properly.