72 Ignition wiring gets hot

[Supertommy68]

I have a 72 Cheyenne Super 4x, 1/2 ton, 350/TH350 and some questions-
first, Years ago, put Mallory unilite in with promaster coil. Ran the original coil wire to the new coil way back when. The wire gets real hot when the key is on (not running). Like melting hot. Why? Its been melted so many times I have cut it back to where its only 6" sticking out at the firewall and spliced.

Second, I have a new replacement harness (form LMC). This has the yellow wire coming from the starter, which looks like its supposed to go to the coil. I am ditching that Mallory and promaster and am putting in an HEI. Does this yellow wire power the coil? Or do I hook up to the wire that gets hot when the keys on?
I have a rats nest of wires, hence the replacemnent harnesses. Any help is appreciated. I don't want a fire.

[bosco200]

Is there only one wire getting hot and melting the ones around it....please be careful my truck almost caught fire about a month ago because of wiring issues and my wiring was fried from the battery to the ignition.
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[BAGNDRAGIT]

sounds like you have a bad ground somewhere, and if you search the forum there are wiring diagrams showing the entire truck..

give a holler if you need more help.

[Monty]

if you are installing HEI, you need to run a new 10 or 12 gauge wire from the IGN terminal on the fuse block to the distributer. the factory wire will not support the added load the HEI puts on the circuit.

Summit and Year One sell a new replacement wire for this. Year One part # 00510

[BAGNDRAGIT]

Monty is dead on, thwe factory wire is a resistor wire and will supp,ly 12v initally but after heating up it will drop to about 9.5v. which will not support and HEI. you can buy the wire from where Monty stated, or you can just get the connectors and a piece of standed 10 or 12 ga wire and do it yourself. i dont know how much the part is though. i have more wire laying around than i know what to do with.........see what happens when you get into the electrical engineering field....

[Supertommy68]

Thank you all for the advice.
It is only that one wire getting hot, thankfully. Since its a resistor wire maybe the aftermarket coil draws too much or something.

I did get a color wiring diagram and the factory (repro) wiring diagrams, but was unable to find an HEI setup in the books I have. Maybe they didn't have it yet.

So the new wire to the HEI is off the key-on, right?

Then this still leaves the yellow wire thats coming off the starter. What should I do with that? I guess a better question is what did it do in the first place?In the rats nest I now have, that wire has been cut off and taped for a while, and the truck runs without it. I'd love to post pics of the way it is now but its pretty embarrasing. Can't wait to get this wiring cleaned up and safe again. Thanks for all the help.

[BAGNDRAGIT]

you should have 12v keyed power going to the coil. (this is the wire that needs to be replaced) and then you should have a 12v keyed(start) wire going to the starter. i will look when i get home and see how mine is hooked up, i dont remember.

this might help.

[Monty]

the wire going from the starter was to bypass the resistor wire while the starter is engaged. this puts full 12V to the ignition while the engine is starting. the HEI does not have an input for that wire, and is (or should be) already getting the full 12V anyway.

the pre-made wire from Year One or Summit is ~$10 or so. i've made them myself, and i've bought them. it depends on if i have the connector for the distributer end to work with, and if a splice in the wire will matter cosmetically.

[doodah man]

I switched over to hei this past weekend. I ran a 12 ga wire from the ign unfused terminal under the dash through the grommet for the speedo cable to the hei bat terminal. Both ends are attached by female spade connectors. I taped off the yellow wire that was connected to the points coil and left every thing else as is. I don't know if leaving the old wiring is a problem, but my new wire gets 12+ volts at all times and the truck is running great.
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[lt704]

It is hard to see on my msd coil pack on my hei where the battrey terminal and where the tach wire goes? Does anyone know if the yellow wire is on the left or right on the coil?. Thanks Russ

[Supertommy68]

Originally Posted by Monty

the wire going from the starter was to bypass the resistor wire while the starter is engaged. this puts full 12V to the ignition while the engine is starting. the HEI does not have an input for that wire, and is (or should be) already getting the full 12V anyway.

the pre-made wire from Year One or Summit is ~$10 or so. i've made them myself, and i've bought them. it depends on if i have the connector for the distributer end to work with, and if a splice in the wire will matter cosmetically.

Monty-
Now I know what that yellow wire did. I guess I will be taping it off like doodah man did. I should be getting my new wire from yearone this week. I bought a tach wire from them too. I don't know if I really needed it. I have a factory tach dash cluster sitting in a box on the shelf and want to put that in soon. Thanks to you all for the help. Its a real confidence boost to know there are guys out there that know how to do this stuff right. My prior methods were limited to tie wire and duct tape.

[70STOVEBOLT]

Originally Posted by BAGNDRAGIT

you should have 12v keyed power going to the coil. (this is the wire that needs to be replaced) and then you should have a 12v keyed(start) wire going to the starter. i will look when i get home and see how mine is hooked up, i dont remember.

this might help.

So is that wire from the neutral safety switch the yellow one? Mine has had the yellow wire taped off since I got the truck. It will start in any gear so the neutral safety switch is not working.

[Supertommy68]

Stovebolt, I think the purple wire to the starter, from the switch, goes through the neutral switch. Don't have the diagram in front of me, but I think thats how it goes.

[70STOVEBOLT]

If that's the case, and mine will start in any gear, does that mean the N.S.S. is bad?

[Supertommy68]

Thats a better question for Bagndragit probably, but here's my deal- Mine starts in any gear too. Bout 10 years back, I sold my original tilt steering column (stupid). The buyer installed a van tilt as part of the sale. Since then, i haven't had NSS or reverse lights. I recently bought a tilit column out of a cheyenne parts truck. It is the same as the one I used to have. the NSS and reverse switches are on the column at the bottom. For many years I thought they would be on the tranny. I don't drive the truck much, so didn't much care. Anyways, now I know the van-tilt didn't have the switch on it, so it has not been hooked up at all for a long time. Theoretically, I would think the truck wouldn't start at all if the switch was disconnected or bad. It makes no sense to me, unless someone jumpered the wire to bypass the switch. Thats why I said its probably a Bagndragit question, or maybe a new thread to garner some more interest in the topic. Sorry I couldn't help more.

[70STOVEBOLT]

Mine was originally a 3OTT and I bought the trans, column linkage, everything I needed to convert it to an automatic. It has always started in gear since the conversion. It doesn't bother me but I always worry when someone borrows it that's not familiar with it.