factory tach question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

love it loud · 08-16-2003, 08:29 PM

I pulled the instrument panel out of the cab along with all the wiring and I want to use just the tach in it for engine break-in. (have separate mechanical oil press. and water temp. gauges to use, but no tach..) Question is, there's a three-wire plug on the back of the tach, and the distributor only has a one-wire plug for the tach.. The only thing I can think of is that maybe the other two wires are a power and ground? Not sure exactly how the factory tachs work.. if they're just energized from the distributor or if they need a separate power and ground. If so, could i just run a power and ground wire directly to the battery for now? Just need it hooked up to watch the rpm's during break-in. Thank you for any knowledge bestowed upon me regarding this subject!

75stepside · 08-16-2003, 08:57 PM

i've got a factory tach... and the harness... and that is the hook up! one to the dist, one pos and one neg.

ElGracho · 08-16-2003, 09:17 PM

Yep, that's right. The tach is marked on the back too, so you can use it to figure out which wire is which.

love it loud · 08-16-2003, 09:24 PM

sweet! good guess!!!

btw.. what's a factory tach worth? can't even find em aftermarket..

**N2TRUX** · 08-16-2003, 11:00 PM

Just the tach by it's self has some value, but not as much as the whole assembly. I would say 50-75 for a good working tach that has had the face and needle reconditioned.

08-16-2003, 08:29 PM	#1
love it loud Calibration Engineer Join Date: Oct 2002 Location: Windsor, Ontario, Canada Posts: 361	factory tach question I pulled the instrument panel out of the cab along with all the wiring and I want to use just the tach in it for engine break-in. (have separate mechanical oil press. and water temp. gauges to use, but no tach..) Question is, there's a three-wire plug on the back of the tach, and the distributor only has a one-wire plug for the tach.. The only thing I can think of is that maybe the other two wires are a power and ground? Not sure exactly how the factory tachs work.. if they're just energized from the distributor or if they need a separate power and ground. If so, could i just run a power and ground wire directly to the battery for now? Just need it hooked up to watch the rpm's during break-in. Thank you for any knowledge bestowed upon me regarding this subject! __________________ CANADIAN CONNECTION

08-16-2003, 09:17 PM	#3
ElGracho Gentleman Jim Driver Join Date: Nov 2002 Location: Poulsbo, WA Posts: 1,553	Yep, that's right. The tach is marked on the back too, so you can use it to figure out which wire is which. __________________ Joe '75 GMC Gentleman Jim '84 Chev C10 Short Wide - Super duper plain (manual steering, manual brakes, no dome light, no cig lighter) '85 Chev C10 Short Wide - Super plain Vortec 4.8 4L60E trans also: '81 K30, '83 C30 Crew Dually, '84 M1028 CUCV, '85 M1009 CUCV, another '85 C10 SWB, '89 R3500 Flatbed

08-16-2003, 09:24 PM	#4
love it loud Calibration Engineer Join Date: Oct 2002 Location: Windsor, Ontario, Canada Posts: 361	sweet! good guess!!! btw.. what's a factory tach worth? can't even find em aftermarket.. __________________ CANADIAN CONNECTION

08-16-2003, 11:00 PM	#5
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,021	Just the tach by it's self has some value, but not as much as the whole assembly. I would say 50-75 for a good working tach that has had the face and needle reconditioned. __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

08-16-2003, 08:57 PM	#2
75stepside Proud Member Join Date: Nov 2002 Location: Pittsburgh, PA Posts: 741	i've got a factory tach... and the harness... and that is the hook up! one to the dist, one pos and one neg.



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