Can anyone identify the terminals on the back of the 1975 tach.
There are 3 male spades, I know they are for Lamp, ground, signal wires, just dont know which terminals are which. I'm using this tach in a 68 with an Gen3 LS6 conversion along with a Dakota tach signal unit.
Thanks

 

My 78' wiring diagram shows a white wire from the dist, black to ground and pink/black from the fuse box. There is a separate bulb that plugs into the back of the tach at least on my 78'

 

can you disconnect one at a time? then see what works and what doesnt?

 

If you take the cover off where the spade terminals are, the printed circuit board has the terminals labled. They should be for the ground, 12 volts, and to the tach terminal on the hei. Not necessarily in that order. And no don't start hooking the wires up and guessing or you will be looking for another tach.

 

If you are looking at the terminals on the tach board or looking at the back side of the tach with the plastic cover on it, you will have three terminals to look at! There are two on the top and one on the bottom of the tachometer. Looking at the back of the tachometer (from a 1975-1977) with the terminals to your right the plugs are as follows. (If it is an original 5658645 A board, it will not be marked as to which wires go where).

Left top plug is positive, Right top plug is ground and the lower plug is your pulse wire from the distributor. Below is the order of the wires with P = pulse. (Remember this is holding it in your hand and looking at the back. . . with the top of the tach up) If you wire it wrong you will fry the board.

+ -
P

As mentioned, the wire on a 1975 to the tach was a white wire that ran from the distributor to the tach.

You do realize you should also run a tach filter in this system to avoid spikes to the tachometer from the HEI distributor.

You can test the tach real easy before you install it too!

When the ignition key is turned in the on position with out starting the car the tachometer is powered up! When powered up the tach should go to zero instantly. This is the same as doing a hardwire test!

If you run 12 volts to the positive side and a verified ground to the ground side, and the tachometer instantly hits zero! It is waiting for pulse from the distributor. Run a wire from the distributor (tach connection) and start the car. The tach should work. Might save you some time if you want to verify the tach is good before installing it in the car.

If you need more help email me direct at Willcoxcustomerservice@willcoxcorvette.c om I think I have a picture of this board with the terminals marked. I'll have to check, but if I do I would be happy to send it to you.

Willcox

 

http://forums.corvetteforum.com/show....php?t=2033600

 

Why did you choose the 75 tachometer? Why not move up to a later model? Was your choice made for you by the way the tachs are put together? 75-77 only being the one that fits stock dash pads? I am going to be going down this road sometime soon and would like to know.

Thanks.

 

75-77 will fit in the dash can for the 1968-1974 cars. 1978-1982 tach will not.

Willcox

 

I have the same set up (LS6 in a '76) and I was starting to look at how to make the stock tach work. What is a Dakota tach signal unit and how does it hook up and work?

 

The wiring harness is a 1968, so wire colors dont help me.
Thanks Wilcox and Carriljc, exactly what I needed.
No Hei on this one.
It's a 2002 LS6 I installed in a red 68 roadster, planning on taking it on Hot Rod Power Tour next week. So on a strict time schedule.
All LS engines use a 4 cylinder tach signal as the signal is from one bank of coils. The Dakota unit is supposed to change it to whatever is needed. Used the 75 tach 'cause it fits the dash. Refaced all the gauges white. You can read the preview story about this car in next months Popular Hot Rodding magazine. BTW, that's my 730 hp LS7 in Car Craft and CHevy High Performance, July 08 issues.
I appreciate all the suggestions.
Thanks
Jeff

 

If the Dakota will change the pulse signal to the tach, then run it to the pulse connector and you should be fine. I do not know anything about the Dakota, but I do know about the factory tachs.

All you need is power, ground and a signal to make it work.

w