Tachometer and Cab Hole Questions

[1970GMC350]

Hello all! Forgive me if my questions sound really dumb, I'm a newbie when it comes to all of this. I'm learning as I go along when I'm working on my 1970 GMC and loving every second of it. Now, onto my questions.

I'm wanting to wire a tach up. Can I wire it into the distributor? In the blue circle, it's stamped "Tach Bat". I believe this is an HEI ignition as I couldn't find my ignition coil anywhere.

Forgive the cobbled up wiring in the background. I need to put a new engine harness in. A prior owner didn't do a very good job at splicing and cutting wires.

Also, the firewall holes mentioned in this post
https://www.67-72chevytrucks.com/vbo...d.php?t=722258

Did every truck that rolled off the line have every one of these holes? The hole labeled "clutch rod" in the first picture and "trans linkage" in the second is uncovered on my truck. I want to make sure there's nothing missing on my truck that I'm not aware of and plug that hole.

Thanks in advance for any help!

[Palf70Step]

Yes that is where you hook up the tach pickup. Far as the holes, they all came with all the holes. There is plugs to cover the unsed holes, but I know myself finding a factory clutch plug seemed to have been hard. On my old truck when I went automatic I just welded up any of the unused holes.

[bluek5]

Here is another thread on the subject.
http://67-72chevytrucks.com/vboard/s...ight=tach+wire

[1970GMC350]

Thank you for your help!

[BigBird05]

That yellow wire that is suppling voltage to the dist looks a little suspect. Make sure you are getting a full 12V on it when cranking over the engine. When people add HEI ignitions they sometimes don't change the resistance wire to a regular wire. If you want to change it over to the factory correct color wire it would be a 14 gauge pink wire. You can also get the correct connector that locks the wire in to the dist.

[GMCPaul]

Both the 67-70 Firewall Clutch Delete Plug and the 71-72 Firewall Clutch Delete Plate & Gasket are reproduced. You'll find both on the following page of our website
https://gmcpauls.com/rubber&ws1.htm
67-70 Firewall Clutch Delete Plug

71-72 Firewall Clutch Delete Plate & Gasket

Paul Jr @ GMCPauls

[bry593]

Originally Posted by BigBird05

it would be a 14 gauge pink wire.

12 awg gxl (general purpose cross linked jacket)

[1970GMC350]

Originally Posted by BigBird05

That yellow wire that is suppling voltage to the dist looks a little suspect. Make sure you are getting a full 12V on it when cranking over the engine. When people add HEI ignitions they sometimes don't change the resistance wire to a regular wire. If you want to change it over to the factory correct color wire it would be a 14 gauge pink wire. You can also get the correct connector that locks the wire in to the dist.

Thank you for pointing that out! I'll change that out along with the engine harness. This is the mess of wiring on the passenger side of the engine compartment. The headlight wiring harness used to look similar to this. I tried to make sense of it but ultimately had to get a new one. The previous owner really jimmied it together.

[pjmoreland]

The following thread has information on installing an HEI BATT wire.

https://67-72chevytrucks.com/vboard/...d.php?t=708975