Tach wiring question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tim R · 05-13-2011, 03:22 PM

I just got a restored tach dash for a guy here locally and was wondering if i need to ground the stud that sticks out of the tach above the 2 spade connectors on the tach . I got the tach wiring harness also but there was no provisions in the wiring kit for a ground . Also in the instructions it doesnt say anything about a ground

Thanks Tim

smorg007 · 05-13-2011, 03:31 PM

Quote:

Originally Posted by Tim R

I just got a restored tach dash for a guy here locally and was wondering if i need to ground the stud that sticks out of the tach above the 2 spade connectors on the tach . I got the tach wiring harness also but there was no provisions in the wiring kit for a ground . Also in the instructions it doesnt say anything about a ground

Thanks Tim

Hi Tim,

Yes you must ground the tach to a good ground source and the stud that stick out above the spade connector. I fried two tachs before I asked the same question. Grounded as above for third tach and have not had any issues since. Good luck.

**leddzepp** · 05-13-2011, 03:59 PM

The tach grounds throught the gauge panel...but it is not a bad idea to add another ground to it to make sure it is well grounded and doesn't fry, as pointed out above.

smorg007 · 05-13-2011, 04:06 PM

By the way, the two that fried were reproduction tachs and the third is an original GM OEM used tach. Don't know if that made a difference or not. None of the supplied instructions or the provided harness included any reference regarding the need to ground.

ChevyLvr4Life · 05-13-2011, 04:09 PM

That's odd, I've never heard of grounding the tach before, not disputing what you are saying, just haven't heard of it. I bought a used tach dash and swapped out my non gauge dash. Got me a tach harness and hooked it up. I had to move some wires around in the non gauge dash plug per GMC Paul's website to make the tach dash work. Didn't ground it, has been in the truck for over 2 years, so far so good.

**leddzepp** · 05-13-2011, 04:11 PM

Quote:

Originally Posted by ChevyLvr4Life

That's odd, I've never heard of grounding the tach before, not disputing what you are saying, just haven't heard of it. I bought a used tach dash and swapped out my non gauge dash. Got me a tach harness and hooked it up. I had to move some wires around in the non gauge dash plug per GMC Paul's website to make the tach dash work. Didn't ground it, has been in the truck for over 2 years, so far so good.

It is grounded through the gauge cluster.

smorg007 · 05-13-2011, 04:17 PM

Quote:

Originally Posted by leddzepp

It is grounded through the gauge cluster.

Hey leddzepp, is this grounded through the wiring plug harness since the bezel is plastic. It's possible I may not have had a good connection although everything was working in the cluster without issue. (Except the tach)

**leddzepp** · 05-13-2011, 04:23 PM

All of the gauges mount to the tin. There should be a wire that runs from the tin to the dashboard (cab) that subsequently grounds all of the gauges in the cluster. My temp gauge quit working once. For whatever reason, it was not grounded well to the tin, so I ran a separate ground wire directly from it to the dashboard. You can also do the same for the tach if you are concerned about frying it.

smorg007 · 05-13-2011, 07:33 PM

Thanks ledzepp, you solved my mystery. I did not have the ground wire you mentioned on my tin when I bought the truck, but now I do.

**leddzepp** · 05-13-2011, 07:47 PM

Good deal! I hate to see someone fry a tach....they ain't cheap (I don't have to tell you that!)

Longhorn Man · 05-13-2011, 08:02 PM

the inst panel is supposed to be grounded twice. Once through the harness, and once through a ground strap that clips to the tin, and to the dash.
I ALWAYS recomend to people to make a ground strap. Been saying it on here for 10 years now. A lot of headaches can be avoided.

Tim R · 05-13-2011, 09:03 PM

Great information , I thought I read somewhere here that it needed to be grounded. The stud has a G next to it so I was pretty sure it needed grounding

Thanks Guys

bmfm64 · 06-10-2011, 12:05 AM

I have a question about the other wires... Red/Pink? to fuse box, Keyed or constant power? And brown to coil... I'm running an HEI, can I simply plug the brown into the tach spade with the correct end installed?

John Gilbert · 06-10-2011, 12:55 PM

Here's a link to a story I did on my '68 GMC adding a tach cluster with an HEI. http://www.customclassictrucks.com/t...er_wiring.html

05-13-2011, 03:22 PM	#1
Tim R Registered User Join Date: Jan 2009 Location: bmt,tx Posts: 127	Tach wiring question I just got a restored tach dash for a guy here locally and was wondering if i need to ground the stud that sticks out of the tach above the 2 spade connectors on the tach . I got the tach wiring harness also but there was no provisions in the wiring kit for a ground . Also in the instructions it doesnt say anything about a ground Thanks Tim

05-13-2011, 03:59 PM	#3
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,031	Re: Tach wiring question The tach grounds throught the gauge panel...but it is not a bad idea to add another ground to it to make sure it is well grounded and doesn't fry, as pointed out above. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul

05-13-2011, 04:06 PM	#4
smorg007 Registered User Join Date: May 2010 Location: Redding, Ca Posts: 371	Re: Tach wiring question By the way, the two that fried were reproduction tachs and the third is an original GM OEM used tach. Don't know if that made a difference or not. None of the supplied instructions or the provided harness included any reference regarding the need to ground.

05-13-2011, 04:09 PM	#5
ChevyLvr4Life Registered User Join Date: Aug 2010 Location: Martinsville, VA Posts: 150	Re: Tach wiring question That's odd, I've never heard of grounding the tach before, not disputing what you are saying, just haven't heard of it. I bought a used tach dash and swapped out my non gauge dash. Got me a tach harness and hooked it up. I had to move some wires around in the non gauge dash plug per GMC Paul's website to make the tach dash work. Didn't ground it, has been in the truck for over 2 years, so far so good. __________________ 1970 Chevy C10 LWB 307 3OTT 3.73 gear

05-13-2011, 04:23 PM	#8
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,031	Re: Tach wiring question All of the gauges mount to the tin. There should be a wire that runs from the tin to the dashboard (cab) that subsequently grounds all of the gauges in the cluster. My temp gauge quit working once. For whatever reason, it was not grounded well to the tin, so I ran a separate ground wire directly from it to the dashboard. You can also do the same for the tach if you are concerned about frying it. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul Last edited by leddzepp; 05-13-2011 at 04:31 PM.

05-13-2011, 07:33 PM	#9
smorg007 Registered User Join Date: May 2010 Location: Redding, Ca Posts: 371	Re: Tach wiring question Thanks ledzepp, you solved my mystery. I did not have the ground wire you mentioned on my tin when I bought the truck, but now I do.

05-13-2011, 07:47 PM	#10
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,031	Re: Tach wiring question Good deal! I hate to see someone fry a tach....they ain't cheap (I don't have to tell you that!) __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul

05-13-2011, 08:02 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Tach wiring question the inst panel is supposed to be grounded twice. Once through the harness, and once through a ground strap that clips to the tin, and to the dash. I ALWAYS recomend to people to make a ground strap. Been saying it on here for 10 years now. A lot of headaches can be avoided.

05-13-2011, 09:03 PM	#12
Tim R Registered User Join Date: Jan 2009 Location: bmt,tx Posts: 127	Re: Tach wiring question Great information , I thought I read somewhere here that it needed to be grounded. The stud has a G next to it so I was pretty sure it needed grounding Thanks Guys

06-10-2011, 12:05 AM	#13
bmfm64 Registered User Join Date: May 2011 Location: Covington, Wa Posts: 5,240	Re: Tach wiring question I have a question about the other wires... Red/Pink? to fuse box, Keyed or constant power? And brown to coil... I'm running an HEI, can I simply plug the brown into the tach spade with the correct end installed? Last edited by bmfm64; 06-10-2011 at 11:37 AM. Reason: fat fingers

06-10-2011, 12:55 PM	#14
John Gilbert Registered User Join Date: Sep 2009 Location: Placentia, California Posts: 567	Re: Tach wiring question Here's a link to a story I did on my '68 GMC adding a tach cluster with an HEI. http://www.customclassictrucks.com/t...er_wiring.html

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