where to drill hole in firewall for factory tach wire

[mikedethlefs@gmail.com]

Looking for info on where to drill hole for factory tach wire to pass through?

[Captkaos]

Historically I ran the wire from an existing pass through.

[mikedethlefs@gmail.com]

I have an 84 C10 and I'm installing a cluster with the factory tach and need to know to drill the hole in the firewall to run the aftermarket tach harness with grommet. just trying to make it look correct!

[JohnnyPopper]

Isn't there a spare spot on the wiring termination block?

[bd]

Not a definitive answer, but from ancient recollection the tach wire passed through a one-wire grommet similar in appearance to the one imaged below.  The grommet passed through the firewall somewhere within the yellow oval.  The difficulty in ID'ing an exact location is that few 80's trucks were delivered from the factory with on OEM tach.  You may need to attend truck shows and pay close attention to determine grommet position more accurately.

If you are not insistent on an OE appearance, using an empty cavity through the firewall bulkhead connector is a clean solution.

[JohnnyPopper]

It's clear that GM factored in the option of a tach. Why would they decrease their profit margin by calling for a retrofit of a single wire? Time/profit???

Why make another hole when there are available slots on the 'firewall bulk connector" ? The cleaner the better!!!

[mikedethlefs@gmail.com]

I'll put a hole in the firewall in the marked area. When I did my Monte Carlo there was a dimple to mark where to drill. I figured GM usually makes things easy but maybe this option was so few they didn't mark a place.
Thanks for the rapid response.

[VileZambonie]

drill it wherever you want but the factory tach wire was below the bulkhead connector