Need tach help, please! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**68350** · 03-18-2006, 09:13 PM

I have a factory tach in my 70 chevy and it doesn't work. I have the brown going to the neg on the coil and the pink going to the fuse box. My test light says I have power all the way to the end of the harness where it plugs into the tach on the back. How can I check the tach to see if it is good or not? thanks

greenhorn male · 03-18-2006, 09:27 PM

I simply connected a portable engine analyzer to the coil neg and battery, then do the same with your tach under the hood. Make sure your connections are good and you're not using too small of a wire guage. I used alligator clips as test leads and noticed that the the tach I tested this way didn't respond with small guage wiring until I switched to larger wire. My 2 tachs and engine tester all had different reads.

**68350** · 03-19-2006, 01:11 AM

so you are saying to use something like a VOM meter and hook one lead to the coil neg and the other to the battery. then connect what for the tach? what kind of readings should I get? Sorry, it just confused me...

JimKshortstep4x4 · 03-19-2006, 07:59 PM

If the wires from the coil and fuse panel are hooked to the right terminals on the tach with the case of the tach grounded it should work. If it does not work then there is probably an internal problem with the tach itself.

I believe that greenhorn male was using an engine analyzer with the
analyzer set up so that it was acting as a tachometer. It appears that he got three different rpm readings with three different tachs.

Jim

03-18-2006, 09:13 PM	#1
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Need tach help, please! I have a factory tach in my 70 chevy and it doesn't work. I have the brown going to the neg on the coil and the pink going to the fuse box. My test light says I have power all the way to the end of the harness where it plugs into the tach on the back. How can I check the tach to see if it is good or not? thanks __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

03-18-2006, 09:27 PM	#2
greenhorn male Senior Member Join Date: Jan 2003 Location: Bay Area, Northern California Posts: 1,344	Re: Need tach help, please! I simply connected a portable engine analyzer to the coil neg and battery, then do the same with your tach under the hood. Make sure your connections are good and you're not using too small of a wire guage. I used alligator clips as test leads and noticed that the the tach I tested this way didn't respond with small guage wiring until I switched to larger wire. My 2 tachs and engine tester all had different reads. __________________ 03 Tahoe 72 GMC Super Custom 2500 Custom Camper, my reliable workhorse. Dual gauged tanks, dual battery trays.

03-19-2006, 01:11 AM	#3
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: Need tach help, please! so you are saying to use something like a VOM meter and hook one lead to the coil neg and the other to the battery. then connect what for the tach? what kind of readings should I get? Sorry, it just confused me... __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

03-19-2006, 07:59 PM	#4
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: Need tach help, please! If the wires from the coil and fuse panel are hooked to the right terminals on the tach with the case of the tach grounded it should work. If it does not work then there is probably an internal problem with the tach itself. I believe that greenhorn male was using an engine analyzer with the analyzer set up so that it was acting as a tachometer. It appears that he got three different rpm readings with three different tachs. Jim



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