Hey, guys the new kid on the block.I just brought home my first corvette(1978) and the tach doesn't work.I found that someone replaced the circuit board on the back of the tach,but had the studs reversed so they were not making contact.I corrected the stud issue ,but now the needle at an idle is below zero rpms. and when I rev the engine it gets to about 1800 rpms and drops to zero again. I's this a ground or short problem ??? Also the temp gauge isn't hooked up at the sending unit in the drivers side head,but there isn't a visible wire disconnected,what color wire am I looking for?? THANKS FOR THE HELP!!!!!!!!!!!

 

Welcome to the site racerx, you should be able to get alot of questions answered here, I also have a '78 that I have done quite a bit work on including the tach. I installed a new control board on the back and it still did'nt register correctly, it just so happens there's a speedo shop about 30 mi. from my house, I took the tach to him and he callibrated it on the spot, if the board is the same as mine you can adjust it by the pot on the front of the board, you'll need aa electronic tune-up tach to use as a reference. The water temp sending unit wire is green with a single clip for the sending unit, the wire breaks out of the harness with or near the alternator wires. You may also want to look at the post titled 72 motor 77 vette for more on C3 wiring, have fun.

 

78Buckshot is right, it may need to be calibrated, this is a good website for info, ideas, or help, http://www.corvettemagazine.com/2006...meter_tach.asp. I would think if the board was fried you'd have nothing. Also, if your running any thing else than stock equipment, i.e. an MSD starter, that was my key to fixing my tach. As far as the Green wire for the temp gauge, make sure the prior owner did'nt tuck it in any of the conduits that the wires run in. I am sure alot of people will tell you, get a shop manual, assembly manual, and anything else that might help you learn. Good luck with the new vette.