HEI Wiring Question/Is This Right

[72 Cheyenne K20]

I have a 72 Blazer w/a 350. Hei is already installed but the wiring is really funky. They had some kinda vacuum module hooked up between the dizzy and the carb. It had wiring connected to it that went through the firewall to another module and a hot lead to the fuse block. I unplugged it from the fuse block while the engine was running and there was no change, so it's gone. Now, I just wanted to make sure that I'm hooking up wires correct.

1) The pink wire that comes out of the firewall that splits into 2 yellow wires (1 to the coil and 1 to the starter) needs to be replaced with a 10 gauge wire that goes to the positive side at the dizzy and no yellow wire to the starter anymore.

2) The only wires going to the starter are the positive lead from the battery and the purple wire from the firewall.

Is it that simple or am I missing something. Any help would be great.

Thanks, Scott

[JimKshortstep4x4]

Scott,

It is simple and it sounds like you have it figured out.

The vacuum switch that you removed is part of the TCS system (Transmission Controlled Spark) that was installed on the trucks and Blazers.
It controlled when the vacuum advance could operate based on temperature of the engine and if the transmission was in high gear.

Jim

[shifty]

http://67-72chevytrucks.com/vboard/s....php3?t=148346 (scroll through this for lots of pics on HEI setup and rewire)

Your setup is wrong w/pink+yellow split wire. You should have only two wires, no splits -

1) The pink wire from the firewall to the coil.
2) The purple wire from the firewall to the starter.

The pink wire will be constant voltage when key is in the ON position and the purple wire goes to the starter and supplies power when the key is turned to the crank position.

[pjmoreland]

You should eliminate the pink and yellow wires and run a 10 gauge wire from the "Ign Unfused" terminal on your fuseblock straight to the "Batt" terminal on your HEI distributor. The original factory ignition wire drops the voltage too low for the HEI to work properly.

[67chevemall]

^ what he said! Plus they can burn up real hot! maybe even ignite.

[shifty]

10 gauge is excessive. I got some 12 gauge from Home Depot (pictures are in the link) and that was fine. The important part is that you don't use the stock white-cloth wrapped wire, there are no splits or T's in it anywhere and it goes direct from the firewall block to the HEI coil terminal. The wire should be gas and oil resistant also (it should say on the wire sheathing).

Are you sure you would run it unfused? By doing that, if it ever shorts out on the block (from heat) and ground to something, guess what you're going to be melting?

I would put a fusible link in-line as close to the firewall block as possible.

[pjmoreland]

I'm pretty sure the stock ignition wire is unfused, other than the 16 gauge fusible link that connects the battery to the electrical system. I agree that 10 gauge is overkill since the red wire feeding the entire electrical system is only 12 gauge to begin with. I can't imagine it could hurt anything by using 10 gauge though, and it certainly can't hurt to put a fusible link in there. I used the HEI power feed wire from a late '70s truck with the original connector on the end. It looks like it's a 10 or 12 gauge wire.

[JimKshortstep4x4]

Cheyenne 20 has the wire harness apart and he is right the pink wire connects to two yellow wires. One goes to the coil the other goes to the starter. He is planning on eliminating the stock hookup including the pink and yellow wires. I assume that he is terminating the new ignition feed wire to a spade which plugs into the original firewall connector. Whether he does that or routes the wire inside to the ignition unfused is a matter of choice. We have done dozens of the conversions and prefer to hook up the coil wire to the outside connector in the stock location for appearance.

Here is a picture of the stock coil wire. The pink wire, and most of the yellow wires are inside the harness.

Jim

[shifty]

If you need one of the bulkhead spade type connectors, PM your address over and I'll send one or two to ya (gotta find em first they're in the garage somewhere!!).

Expect it won't be there till next week though :\

also - seriously, check out the FAQ article I linked up up above, it has lots of good info about the rewire

[pjmoreland]

Hey Shifty, that's a nice writeup! I really like the idea of connecting the ignition power wire to the original connector. That's clean. Where did you get those spade terminals?

[72 Cheyenne K20]

Thanks for all the help guys. Thanks for the link shifty, that helps!. Hey JimK, thanks for that bit of info on the TCS system. I thought it looked factory but I've never seen this installed before. That brings me to my next stupid question, do I need it? Let me know when you get a chance.

Thanks, Scott

[shifty]

Originally Posted by pjmoreland

Hey Shifty, that's a nice writeup! I really like the idea of connecting the ignition power wire to the original connector. That's clean. Where did you get those spade terminals?

Napa. The part number is on that page. They have a little box, they sell them for a few cents each. I owe finding them to the guys here at the forum.

[racer face]

P.J. and Shifty have you on the right track. You need 14volts of power to an HEI distributor.There is a kit you can buy for less than $20.00 from MAD Enterprise(www.madelectrical.com) gives you wire, connectors,tie wraps etc and DIE-RECK- SIONS what ever they are.