Second wire on a coil?

[enkeivette]

So an ignition has two posts, one hooks up to 12v+, what does the other post hook up to?

My dist has two wires coming from it, one red, one black. The red is 12v+, and the black wire goes to the other post on the coil. I would think it was 12v-, but then by process of elimination there is no wire left for the tach signal... Is it the tach signal?

[94cobra69ss396]

The black wire is the negative and it should go to the distributor unless you are running an MSD box. If you're not running an MSD box then the trigger for the tach goes to the negative side of the coil. If you're running an MSD box then there is a seperate wire for the tach. Don't hook the tach up to the coil with an MSD box or you won't get spark. I don't remember what the wire color was on the MSD but I can check my instrutions sheet for the one I installed on the Chevelle if you need me to.

[enkeivette]

No I'm not running a coil, I'm going HEI. I'm just trying to sort out the wires that were attached to the coil. So it sounds like my leftover wire that was on the other post is probably my tach signal wire right?

[kdracer73]

I will post pics in a few...very busy !

[kdracer73]

http://i925.photobucket.com/albums/ad94/kdracer73/parts006.jpg
http://i925.photobucket.com/albums/ad94/kdracer73/parts002-1.jpg

HEI Coil should have 3 wires. In pic 1 the silver strap is a ground through the ign module in the dist, with the 3 wire connector.Here:
http://i925.photobucket.com/albums/ad94/kdracer73/hei012.jpg

Without the ground srtap the coil will work....for 20 min or so before burning out the module.

[enkeivette]

I'm pretty sure my HEI is grounded into the computer. Just wondering if the second wire on an old style coil is the tach output.

[kdracer73]

http://i925.photobucket.com/albums/ad94/kdracer73/hei011.jpg
In this shot....the spade on top right is ign power, the one on the left top is tach feed only. the other 3 are for the 3 wire connector for the module.
http://i925.photobucket.com/albums/ad94/kdracer73/hei012.jpg
The coil ground is fired through the module.
Some later HEI dist have a another 4 wire connector to the pcm for timing control. but should run without it , since base timing is set with it unplugged.

[enkeivette]

So... do you guys think the wire is tach feed, negative, or neither? I'm confused by all posts.

[kdracer73]

I think we are having a information breakdown. Are we talking about factory HEI harness? It would have a pink wire from ign switch-12volts with key on. the OE tach wire should be white. The ground is the dist casing. A HEI only needs a single 12 volt feed to make it work. That is the one in the upper right slot from my picture.

If it has been changed to something else at some time, that does not work the same,...the colors won't match.