Help with OEM type tach upgrade install.

[smorg007]

I finally gave up and purchased the OEM aftermarket tach conversion upgrade for my 72. It installed in the cluster gauge without cause or concern and looks great. I have two questions;
(1) Next step refers refers to using the existing 3/4" hole in the firewall or if you don't have this hole "DRILL IT". Problem is it does not say where this hole should be drilled to match factory placement.
(2) The supplied wiring diagram shows connecting the brown wire to the negative side of the coil with the supplied eye connector. I have an HEI distributor so I don't have this type of coil. My HEI distributor has a male spade connector on the cap for tach, so I assume I can cut the off the supplied eye connector and replace it with a female spade connector and connect as though I was connecting to the neg. side as coil?

If someone can post a picture of where this hole is in the firewall I would appreciate it and let me know how to connect to HEI so I don't damage my hard spent investment.

Thanks in advance.

[OhioDan]

Hope this helps? No, they're not the same pic.

[JimKshortstep4x4]

Here is a pic of a 72 firewall with the factory tach hole. This hole was punched at the factory as can be noted by the lip around the outside of the hole. (The firewall is dimpled so it makes it easier to drill).

Jim

[smorg007]

Thanks for the help.

[WIDESIDE72]

I always wondered what the stock tach hole looke like....

[67Slider]

I just bought the same kit and have the same questions. Do you need an HEI pigtail? I have seen some sell but didn't know if you need it or not. I have also seen some ground from the third post to the metal tin. Is this the ground or does it ground to the tin?

Thanks in advance,
Matt

[smorg007]

Originally Posted by 67Slider

I just bought the same kit and have the same questions. Do you need an HEI pigtail? I have seen some sell but didn't know if you need it or not. I have also seen some ground from the third post to the metal tin. Is this the ground or does it ground to the tin?

Thanks in advance,
Matt

Hi Matt,

I drilled the 3/4 " hole in my firewall where JimKshortstep4x4 pic showed it to be. I then swapped out the circle type spade for a female spade and routed the wires through the firewall and along the factory wire loom and connected the tach wire to the hei male "tach" connection. I then ran a ground wire from a good ground source under my dash and connected the ground to the back of the tach marked ground I then connected the wiring harness to the fuse box and back of tach and everything is working just fine. I did not use the metal tin as my grounding source.

Hope this helps.
Stan

[Andy4639]

The tach should work fine as wired. The pigtail is a option but as smorg007 points out not a have to!
Mine has been installed since 1987 and it worked great until this past winter when I pulled it out of the truck for a new dash altogether.

[67Slider]

Cool. Thanks guys. Truck is in paint jail but I have been tinkering with parts. Just finished the tach dash repaint and refinish.
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