Easiest way to wire up factory tach? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**lks dcvn** · 05-25-2020, 05:19 PM

I'd rather not spend ~$25 to buy a tach harness if I can help it.

Checking to see if this is the correct/easiest way to wire up a tach in my 70 GMC Jimmy. Single wire run to the HEI tach post through the firewall and the other 2 (12V and ground) wires stay local like in the pics below that I found on the forum from older posts.

Thanks.

Andy4639 · 05-25-2020, 05:46 PM

Just run the hot wire to fuse block to unfused 12 volts. You can do it that way but it may not be as good of connection.

**TBONE1964** · 05-26-2020, 02:49 PM

The tach wiring should be at least 14 gauge but 12 is preferred.

Do not tap tach wiring to the cluster hot feed. It is only 18 gauge and the tach needs 12 gauge wire.

The tach will ground to the cluster tin so really no external ground is needed but never hurts. Run the battery voltage directly to fuse panel "ign feed" with 12 gauge wire. Also 12 gauge to the neg side of coil.

**lks dcvn** · 05-26-2020, 05:33 PM

Cluster Feed or Ign Unfused for the tach power?

Thanks for the update. I can easily update the wire gauge and connections now that I have everything apart.

05-25-2020, 05:19 PM	#1
lks dcvn Registered User Join Date: Jan 2007 Location: Columbus, Ohio Posts: 4,348	Easiest way to wire up factory tach? I'd rather not spend ~$25 to buy a tach harness if I can help it. Checking to see if this is the correct/easiest way to wire up a tach in my 70 GMC Jimmy. Single wire run to the HEI tach post through the firewall and the other 2 (12V and ground) wires stay local like in the pics below that I found on the forum from older posts. Thanks. Attached Images

05-25-2020, 05:46 PM	#2
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Easiest way to wire up factory tach? Just run the hot wire to fuse block to unfused 12 volts. You can do it that way but it may not be as good of connection. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

05-26-2020, 02:49 PM	#3
TBONE1964 Cluster King Join Date: Nov 2012 Location: Junction City, OR Posts: 5,263	Re: Easiest way to wire up factory tach? The tach wiring should be at least 14 gauge but 12 is preferred. Do not tap tach wiring to the cluster hot feed. It is only 18 gauge and the tach needs 12 gauge wire. The tach will ground to the cluster tin so really no external ground is needed but never hurts. Run the battery voltage directly to fuse panel "ign feed" with 12 gauge wire. Also 12 gauge to the neg side of coil. __________________ Contact me on all of your gauge cluster needs. I specialize in restoration, repair and parts sales for 67-72 Chevy and GMC trucks. email me at tbonegarris@yahoo.com I am also a dealer for Counterpart for gauge cluster parts only. Also see my facebook page, CG&C

05-26-2020, 05:33 PM	#4
lks dcvn Registered User Join Date: Jan 2007 Location: Columbus, Ohio Posts: 4,348	Re: Easiest way to wire up factory tach? Cluster Feed or Ign Unfused for the tach power? Thanks for the update. I can easily update the wire gauge and connections now that I have everything apart. Last edited by lks dcvn; 05-26-2020 at 05:53 PM.



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