HEI Distributor Internal Wiring Oddity

Congratulations, you have discovered one of the enigmas to engineering...specifically: Why does production not always match design?

Good call, SolarEagle. The lead is apparently the ground side of the coil secondary; via the screw it is clamped to the coil frame, and to the ground strap which is under the coil frame. Note a loose screw here could mean intermittent contact and associated misfiring. Not GM's finest moment.

And watching the link you provide, I notice my HEI is slightly different than the one in the video. Mine has 4 screws which go thru the coil cover, thru the coil frame and into the cap. I don't have separate coil screws and coil cover screws.

Yeah good luck trying to find something like this.... enough to add a few grey hairs I think....

Will it make the engine run?

Isn't that all that really matters?

Probably a ground wire to provide RF shielding. I don't know if this is like yours.

Aha. Just found this pic of an MSD HEI unit. Note there are TWO ground leads, the one from the coil to a screw, and another from a different screw that terminates on the ground strap. Redundancy. I think I'll add this second lead to my HEI.

If you noticed the mention of the low voltage wiring in SE's video, it shoes that the ground wire in the connector is only to supply a ground path for any stray high voltage from the coil or cap. The control unit grounds through the distributer housing. SO... if you attach a jumper wire from a 12 volt source to the red wire in the cap, the one with the + next to it. And you attach a jumper cable from the negative on the battery to the dist. housing, you also will be able to spin that dist. gear and have the 8 plug terminals send lots and lots of voltage to the hand that you are holding that dist. with.

Send photos.

Yes, the control module grounds thru one of it's mounts to the dist body to the engine to the frame or battery. But the HEI coil is different than typical external coils, which are wired like this:

...where the secondary winding is grounded along with the primary winding thru the points. The HEI coil seems to bring out the secondary winding's ground thru the black lead. I checked mine and the only continuity from the HT terminal (on the bottom of the coil as it sits in the dist) is to the black lead. And the black lead goes to a screw that goes thru the coil frame to the ground strap and the strap connects thru the harness to the dist body where it finally gets to ground. I think it looks like this:

...so the black lead and it's partners are essential to getting good sparks where we want them at the plugs. A loose screw could cause sparks inside the coil housing.

Too late to edit my last post, but: the secondary doesn't ground thru the points, but thru the primary winding. I think. It's getting late and I've been going from garage to bed to computer several times already. Goodnight all.

What no MSD 8 box to run that street rod. How did the rear end come out.

The Mallory MaxFire is plenty. I've gone the MSD box route...I think I've had 4 ignitions over the years...an MSD, 2 Mallorys and now the HEI. What is wrong with me?

Lockduke, you remembered my rear end thread which I had completely forgotten! I just updated it, go take a look. Turned out very well.

Done