The Corvette Kid

I put an LS-3 in my 61 vette and I mounted a small Sunpro tach in the inst. cluster. How do I wire the tach since there is no distributor. Thanks, Bob

C1ROD

Is the Sun Pro Tach wire or Cable driven?

see link this may help
http://www.abbott-tach.com/cablex.htm


Answer from Australia

63 grandsport

should of been a tack wire on new wiring harness

John McGraw

Yep, should be a pulse output from the computer that hooks to the tach. The pulse from a LS3 ECM output, usually requires most tachs to be set to the 4 cylinder mode to read correctly.



Regards, John McGraw

1coolC2

Most, if not all of the aftermarket harness's provide the pulse output for the tach and as John stated above, most of the after market tachs require you to set it to the 4 cylinder mode.

If you are using a factory harness from a Corvette/Camaro that you got with the engine from a "pull out", you can look up the pin number on the controller (ECM) for the tach output or perhaps post on LS1.com and someone can provide it to you.

R/
Jeff

Poorhousenext

You can use an RPM pickup from MSD if you do not have a tach signal wire.

http://www.msdignition.com/product.a...721&terms=8918

http://www.msdignition.com/uploadedF...structions.pdf

mikey

note if you get the wire hooked up and are still having problems let us know the issues.. a weak signal from the ecm requires a pull up circuit in a lot of applications and if you can't set the tach to 4 cyl mode you can change the output from the ecm to read like a normal 8 cyl pulse (reportedly). i say reportedly on that last part because i found the section in the ecm to change it but it did not affect my tach which still reads half.. i'm probably going to have to buy the dakota digital unit to convert the signal (this piece will do both frequency conversion and pull up circuit)..

The Corvette Kid

Thanks guys, I took a look at the instruction manual that came with the GM harness and it does come with a wire for the tach, and it does say to set the tach for 4 cyl. As soon as I get my speedo back from the repair shop I will hook it up and see what happens. Thanks again, Bob

CFster

If you can't get the right number of cylinders, then Dakota Digital makes a tach interface. It can accommodate just about any engine swap.

We recently used one with a '67 GTO that we put an LS3 in.

-Colin

mike coletta

Use the tach signal wire from the ECM, and set your tach to 4 cyl. If it doesn't come up right away, you'll need to add a "pull up" resistor. Use a 1K ohm resistor (any size). Put a 12v ignition wire to one side of the resistor, and attach the other side to the signal wire from the tach. Don't cut the signal wire, just tap into it.

Mike Coletta