I am putting a factory electric tach in my 73. Need to know the wiring. As I look at the back of the tach there is a three wire hookup. A single center lug an a left and right double lugs. I am sure it would be a positive wire a negative wire and a tach feed wire. Any help on which one goes where?

 

Are you referring to a Corvette factory tach that was associated w/ a HEI distributer? I can't really help but that info might be helpful for someone here that can. A factory shop manual for a '75 and later should have the wiring diagram for the HEI/tach setup.

 

Yes, it is afactory corvette tach out of a 75-76 corvette. I beleive that some of the 74 also used an electric tach and am not sure when the dash was changed after 76. I also fined it hard to beleive that no one on this sight has a wiring diagram for corvettes during this time period for a C3. Help!!!!

 

Near as I can tell,the white wire goes from the "Tach" terminal on the HEI to the white wire on the tach. The Red wire on the tach is 12V and the black wire is ground. That's on the schematic for my 79. Good Luck!
Ron

 

Thanks for the reply, but no help. If I had the three wire connector with wire in it. I know red is hot, black is ground leaving the white to go to the Dist. I do not have the connector. I need to no what lug is what.

 

Cuda,
Hope this works for you.
There should be 4 wires from the tac

White: to 12V dash lighting
Red: 12V ignition switch or connection on fuse box saying IGN
Black: to ground (your tach may have a built in ground so it would only have 3 wires)
Green: to tach terminal on HEI

Schoon

 

Again thanks, but I do not have a white wire or a red wire or any wires. I have three metal lugs or terminals(spade type) on the back of the tach. One single terminal towards the bottom of tach and two terminals right above it, one to the left and one to the right. Ineed to know to what terminal does the positve wire attach. what tyerminal does the negative wire go to and needless to say the third wire will go to the Dist.

 

I found a post about tachs,the fellow mentioned 3 terminals,one at 9 oclock,one at one and one at four. He was pretty sure the 9 oclock one was the ground,unsure of the other two. Should be easy to determine,ground the 9 oclock,touch 12v positive to one of the others,if the needle goes up,that's where the signal (white) wire goes,if the needle goes down and stops at zero,that's the red wire. You must have the printed circuit on the tach before it will work. I'm guessing that you have because the three flat connectors are what plugs into the dash pcb.
Ron

 

I teach automotive at a college here and do not let my students do "what if test" and I am not to fond of doing them myself. I tried doing an ohms test, but the results were to inconclusive. Since it seems the curcuit board fails with some regularity, i would surly think some one has tested the wiring prior to just replacing the board and therefore knows were there was power,were there was ground and that just leaves signal.

 

Several of the aftermarket Corvette suppliers have a tech section on their website. Might be able to find something there.