6 cylinder tach wire firewall hole location

[Dirt's72]

I am installing a 6 cylinder tach in my 72 using an original tach wiring harness which came from an 8 cylinder 72 big block truck. I'll be using it with a 250 inline 6 points distributor. I know where the correct hole in the firewall is for the 8 cylinder. My question is where is the correct place where a hole would be in the firewall to a 6 cylinder? The brown wire does not look long enough to reach the coil if using the 8 cylinder hole location. Also do I hook the brown wire to the negative side of the distributor or coil? Thanks

['68OrangeSunshine]

Originally Posted by Dirt's72

I am installing a 6 cylinder tach in my 72 using an original tach wiring harness which came from an 8 cylinder 72 big block truck. I'll be using it with a 250 inline 6 points distributor. I know where the correct hole in the firewall is for the 8 cylinder. My question is where is the correct place where a hole would be in the firewall to a 6 cylinder? The brown wire does not look long enough to reach the coil if using the 8 cylinder hole location. Also do I hook the brown wire to the negative side of the distributor or coil? Thanks

Coil.
Splice on a longer wire if the V8 unit won't work.
On the Chevy V8s, the Distributor is at the rear of the engine bay, but L6s have the Coil about the middle of the Passenger Side, and the Distributor forward of that. They likely had an L6-specific tach wire, but that was long ago. Use the V8 hole.
Make an extension of 20 ga wire [yellow] with a ring terminal on the end to reach the Coil. Splice it well and put insulation [tape, heat shrink tubing etc.] over that.

[Dirt's72]

Thanks Orange. I have a cut up tach harness I'll splice and save the good one. The wire is thick though more like a 12 guage. I think I'll just stab it through with the oil pressure tube. Hopefully this thing works.

['68OrangeSunshine]

I have an aftermarket Auto Gage by AutoMeter Tach fixed to my steering column with a hose clamp. Oil Pressure, Vacuum, and Water Temp gauges are mounted in a 'shin-scraper' panel below and right of the dash.
I had this Tach for years before I switched to HEI. I just changed the lead from a ring terminal on the [-] coil post to a Packard connector into ''TACH'' on the HEI Cap. Works great.

[RichardJ]

Instead of punching unnecessary holes in the fire wall, get the correct Packard connector terminals and use unused slots in the firewall/bulkhead plug.

The existing wire for the Dist power is the cloth covered wire in this image. That wire is a Nichrome resistance wire that the guys converting to an HEI dist are so deadly AFRAID of.
That resistance wire terminates inside the harness wrap, along the side of the valve cover. At that point, the resistance wire is spliced together with a wire (typically Yellow) that goes down to the starter solenoid and also another wire (copper) that connects to the coil.