I picked up a vintage Stewart Warner Tach Model number 997RS6. It seems new in the box. I hooked it up to a Chevy 350 with the HEI distributor. Green wire to the Tach connection on the distributor, red wire to the power source and black wire to a ground on the battery. The darn thing won't read the signal from the distributor. The needle moves slightly when it's powered up but it won't register the RPMs.I know that it is getting a good power source and the ground is fine. I also hooked up another tach to see if the signal source in the Distributor was good. It was.
I think that the tach dates back to 1959 and wonder if that has anything to do with it. The Steward Warner tech guy in Canada hadn't seen this tach and couldn't find anything on the internet. Any help would be greatly appreciated. Thanks