72cuttys

Can I use the factory resistor wire to activate a relay and just send 12v directly to my HEI from the battery? If not, what is a good spot to tap into to get 12v keyed?

Found this diagram, however it is for a GTO and I dont not know if they used the same points setup as the olds.

oldcutlass

That will work. The points setup is the same as an Olds.

jensenracing77

X2, It will work but why not just go from the ign terminal on the fuse box? Those relays are fairly reliable but you're relying on the relay to get you home.

jensenracing77

I guess you could keep an extra in the glove box

4speed455

X2 on running a new wire off the IGN spade on the fuse block. You will have to run a 12v wire to that relay anyways. Why not do less work and use less money/parts.

I actually have a M&H engine harness set up with the proper wiring and connectors for an HEI distributor and internally regulated alternator. Mine needed to be replaced and I was able to order to my specs. It looks identical the factory harness except for the mods.

jag1886

Yes you can, I did this on my 65, I just removed as much of the original wire as possible and replaced it with regular wire, works perfect and you won't have some cobbled up looking wiring coming through the firewall.

jag1886

You are missing the point of the relay, you can run a 10 gauge wire direct from the horn relay to supply power to the ignition when you use a relay, this makes for a very reliable power supply for an HEI instead of trying to suck the power off what is sometimes an overtaxed stock fuse box.
Yes I do carry an extra in my tool box right beside the replacement HEI module.

jensenracing77

If you are looking for a more direct power source I can understand but how much amp draw does an HEI coil have?

oldcutlass

If the relay fails, all you have to do is jumper terminals 30 and 87.

dmullin

Your relay idea will work fine. I've had a similar set up on my 70 442 for years.
However, if you are sourcing power from the horn relay stand off, use 10 gauge wire to the relay and from the relay to the coil/module connection.
I suggest a 25 or 30 amp fuse.
14 gauge wire will lose some voltage ,while #10 won't at these current levels and wire lengths.
Also, be sure to buy a minimum 30 amp relay of reputable quality. It will last longer, and have less voltage drop across the internal contacts.
Happy wiring.

72cuttys

All this mention of using the horn relay for a source, what is wrong with just using the battery?

dmullin

There isn't anything wrong tapping off the battery if you fuse it close by.
But the horn relay stand off is intended for branching from, and its closer, neater and also comes from a fusible link source.

72cuttys

Im not currently around my car, where is the horn relay stand off?

dmullin

On most older cars it would be on the firewall, on my 70 442 it is on the inside of passenger fender. Just above the inner fender mounting lip.

72cuttys

Will the horn relay provide 12v while cranking? Or do i need to use the starter wire for that.

jensenracing77

It is 12 volts all the time. Runs from the battery to the terminal, nothing between.

oldcutlass

What determines 12v during cranking are the 2 wires that used to be on the coil positive terminal of your original wiring. There is the resistor wire and the wire provided for the bypass circuit from the starter. In your drawing they are connected to terminal 86 on the new relay.

RAMBOW

This is what I've done on several cars- just cut it back to the minimum length you can safely work with by the connector- strip, then solder on a new wire, cover with heat shrink. Always gotten the full 12 volts afterwords.

72cuttys

I found it, I see what you are saying. I thought you were saying to use the horn relay as a switched 12v source.

I took the carb off last night, might swap my HEI while I have easy access to the dist.

Fun71

I measured mine several yeas ago using a Fluke 189 multimeter in Fast Min/Max mode and the highest reading was just over 5 Amps. I am not 100% certain I was able to capture the peak values with this method, though.

jag1886

You guys are still missing the point of the relay, it has nothing to do with what amperage the ignition is pulling and has everything to do with how much amperage everything else added together is using.
What I mean is you are driving at night with the air on, blower motor on high headlights on high beam and stereo running full blast, that's when that old fuse box is being seriously overtaxed. When you have a stand alone ignition system it has a better chance of not having a voltage drop that could harm something.
Am I making any sense?

oldcutlass

Exactly, with the relay, your ignition load is not going through the cars electrical system. Your guaranteed full battery voltage to the ignition at all times.

Fun71

I missed nothing; I was simply answering the question that was asked.

And are you certain that the fuse box is being "seriously overtaxed" in that situation? I have been there many times and nothing catastrophic happened.

dmullin

Hei ignition systems are designed to run at full electrical system voltage.
The electrical system designed for the original ignition will make the hei operate, but at what level?
Electrical loads don't really pull current. A given voltage will push a given current through a given resistance.
Therefore, if extra resistance is added to the primary ignition circuit by factors such as switch contacts, fusebox and bulkhead connections, in many cases 16 gauge wire and corrosion, you will have an operating voltage drop that induces less secondary current. Less spark.
My point is that by installing a higher output ignition you are requiring more out of the supply circuit than was originally designed for, that's before we account for all the aged parts.