HEI power wiring...

[Jabes1]

I have a 74' with HEI ignition. The factory HEI wiring is completely gone. I have it powered incorrectly and its melting the insulation on a tan wire Im using from the firewall bulkhead.

I would like to properly wire the Positive + power supply to the coil. Looking at the schematic (my interpretation) the + is a 20G Y (Yellow) labeled 20Y 7A which splices to 20Y 7B. The 20Y 7B looks like it attaches to the R terminal on the starter solenoid. Is this correct?

From 20Y 7A it also splices off to 20 P/B 3. What is P/B? is it pink or blue or purple or blue? This wire then appears to terminate at the firewall bulkhead engine harness terminal 3.

The schematic also calls for a 1.35 Ohm resistor for the V8 engine where is splices at 20P/B 3. Do I need the resistor?

Basically do I just need to run a wire from the + Terminal on the coil to the R Terminal on the Starter Solenoid, add in a splice wire back to the number 3 terminal on the firewall bulkhead engine harness?

[Just call me Sean]

This one is easier to read.

[cadillac_al]

Pretty interesting, my 74 still had points ignition.

[geezer#99]

As did mine Al.
All the wiring is gone for the hei because it never existed.
All you need is a dedicated 12v power source for the hei. Either from a 12v spade on the fuse box or from the ignition switch.
The yellow wire and resistance wire are not needed for an hei.

[406 Q-ship]

1974 would be a points ignition system. If you are converting to HEI then you need to replace or route around the resistor wire and up grade to 12 ga wire. I usually will run a bypass wire from the bulkhead connector and where it plugs the original resistor wire in the bulkhead connector. The yellow wire that runs down to the starter is the R wire that supplies power to the coil in cranking. Early ignition switches did not allow power to the ignition system when cranking the engine.

[MJN]

My '74 was also points but I converted to HEI. I removed the factory distributor power wire from a ~76 parts harness I had and replaced the resistor wire my '74 had. Easy swap and looks factory since I used factory wiring.

[Jabes1]

Originally Posted by geezer#99

As did mine Al.
All the wiring is gone for the hei because it never existed.
All you need is a dedicated 12v power source for the hei. Either from a 12v spade on the fuse box or from the ignition switch.
The yellow wire and resistance wire are not needed for an hei.

Okay... this makes sense. I've owned the truck since I was 16/17 and have had the HEI wired this way since I got it. I just recently upgraded to a more powerful coil and maybe thats why its melting the insulation.

[VWNate1]

" Early ignition switches did not allow power to the ignition system when cranking the engine. "

Not sure where you ever got that idea .

The entire point of the second terminal on the starter solenoid was to by pass the calibrated ignition wire from the key switch when cranking so the spark was stronger .

I add HEI systems to everything and my simple method is one of those tiny cube relays that's rated for 50 amperes, kicked by the low power feed (7 ~ 9 VDC) from the key switch .

Easy and doesn't hack up the factory harness and isn't glaringly obvious .

[Jabes1]

Originally Posted by VWNate1

" Early ignition switches did not allow power to the ignition system when cranking the engine. "

Not sure where you ever got that idea .

The entire point of the second terminal on the starter solenoid was to by pass the calibrated ignition wire from the key switch when cranking so the spark was stronger .

I add HEI systems to everything and my simple method is one of those tiny cube relays that's rated for 50 amperes, kicked by the low power feed (7 ~ 9 VDC) from the key switch .

Easy and doesn't hack up the factory harness and isn't glaringly obvious .

The OEM coil will draw 50 amps? I like the idea of running it this way. I need to add a fusible link and I plan on connecting it to the accessory lug on the factory busbar. Do you run a fuse? How big of a fuse is needed?

[VWNate1]

No ;

Either way draws under 15 amperes .

Ignition systems are typically not fused for safety reasons, I don't -ever- fuse them as I don't think I know more than the Engineers .

If it worries you, set up a separate dedicated power circuit and add a circuit breaker .