Weird issue - Just started with Tach addition

[BillgreenC10]

1972 C10. Everything worked fine, I added a Tach from Bothers and everything still worked fine. The Tach was not working though, and I read that the tach itself needs a ground. Others say the tach is grounded and doesn’t need its own ground wire, even though there is a grounding bolt on the back of it.

I didn’t ground it, but everything was still working so I decided I would get to it when I could. It’s been about 4 months.

Just recently, if I turn on the parking lights or headlights, the turn signal indicators on the dash light up. If I activate the left turn signal, the right indicator on the dash flashes, and Vice versa. The turn signals themselves flash correctly based on left or right turn.

Could the lack of the tach ground be it, even though it’s Beem fine for 4 months? I’m gonna add the tach ground tomorrow, but while it’s torn apart I wanted to see if you guys had other advice of things for me to check?

I suck at electrical, so feel free to talk to me like a 1st grader. Thanks for any help.

[PbFut]

I had this exact same issue, though my Tach worked. The odd light issue just started happening one day about 6 months after I installed the tack. I suspected a ground issue and spent a day or two searching all the lighting connections in the the front of the truck. I guess because the turn signal was involved I began to suspect a ground on the cluster could cause my issue . Sure enough, moving some wires in the cluster area gave indication something was amiss. I pulled the cluster and found one of the ground bolts to the circuit board was making less than desirable/intermittent connection. I ran a simple grounding wire hooping to all the ground points on the circuit board and for good measure the Tach pin to a good ground point on the dash. Solved the lighting problem completely. Tach also works flawlessly. One other point. The yellow lead that use to go to the coil that is normally used to power HEI distributors is a Stainless Steal resister wire. It drops voltage about 2v. You should not use that wire to power the HEI. Replace it or bypass it with cooper to eliminate that resistance and get a full 12+ volts.

[RichardJ]

>>The yellow lead that use to go to the coil that is normally used to power HEI distributors is a Stainless Steal resister wire. <<

That almost sounds true.
Only the portion of the resistance wire that has the outer cloth covering is resistance wire. The resistance wire is Nichrome ( nickel-chromium) , not stainless.
The yellow wire from the starter solenoid is copper wire. The resister wire originates at the bulkhead connector and joins the copper wire, inside the wrapped harness. The copper wire then extends on to the distributor. This portion of the connection is copper wire and may still be yellow or not.
The wire from the starter solenoid should be disconnected and/or removed when installing a HEI.