re: wiring question
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77mali
pila
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G3GM :: G3 Tech :: Electrical
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re: wiring question
by alleyball4 Sun Mar 31, 2013 9:22 am
When someone switches from a 350 to a 454, or let's say a 6 cyl to a 350 on a 73-77 car, what has to be changed as far as the wiring harness?
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Re: re: wiring question
by thatfnthing Sun Mar 31, 2013 11:29 am
If we're talking about the engine side, the only concern I can think of would be if you are going to an HEI distributor from points -- the + feed wire will be a resistance wire in points applications to keep from burning out points prematurely. HEI expects a full 12V, so you will need to replace this with a 16ga wire directly from the ignition.
Also, if there's a tach, the HEI has the tach output alongside the + feed, so you will need to get the appropriate pigtail.
Everything else should carry over unchanged.
Also, if there's a tach, the HEI has the tach output alongside the + feed, so you will need to get the appropriate pigtail.
Everything else should carry over unchanged.
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Re: re: wiring question
by 77mali Sun Mar 31, 2013 11:49 am
Agreed.
The only possible differences from model to model might be related to accessories such as A/C, dual horns, etc as far as what you might have versus making one up or buying a used one.
The fuse box on the engine side is broken up into 2 "blocks". One side is for lights, side markers etc. (closest to fender) & the other is for the engine harness which has all the wires you should need for Alt & Starter,etc.
Might be some year to year differences too like the headlamp connectors (rounds are different than quads) but it's mostly minor switching over.
The only possible differences from model to model might be related to accessories such as A/C, dual horns, etc as far as what you might have versus making one up or buying a used one.
The fuse box on the engine side is broken up into 2 "blocks". One side is for lights, side markers etc. (closest to fender) & the other is for the engine harness which has all the wires you should need for Alt & Starter,etc.
Might be some year to year differences too like the headlamp connectors (rounds are different than quads) but it's mostly minor switching over.
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Re: re: wiring question
by pila Sun Mar 31, 2013 12:35 pm
When I switch to an HEI from points type ignition, I feed the HEI with a wire from the fuse block, where there's a tab marked "IGN", which is only powered when the switch is on, and not when the key is turned backward for "accessory". My '74 has been that way since 1990, so I know it works 
A female spade lug works OK to tap into the fuse block male terminal.
A female spade lug works OK to tap into the fuse block male terminal.
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Re: re: wiring question
by alleyball4 Sun Mar 31, 2013 1:40 pm
thanks for the info ....
and yes, I am running an HEI distributor.
and yes, I am running an HEI distributor.
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Re: re: wiring question
by 77mali Sun Mar 31, 2013 1:48 pm
Did all 73's have points & is that yet another 1 year only 73 thing?
When was the switch to HEI?
When was the switch to HEI?
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Re: re: wiring question
by thatfnthing Sun Mar 31, 2013 2:12 pm
IIRC, the switch happened in 74 mid year, so some models had it, some did not.
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Re: re: wiring question
by dynchel Sun Mar 31, 2013 7:40 pm
If you need a harness, I bought one through opg but it was made by m&h electric fabricators. When I called the tech line I was told they can modify harness's to your needs (like a hei in a '73). It sounds like a good place to deal with, my harness is perfect, using factory color wires and looms. There number is (562) 926-9552 if you're interested.
Last edited by dynchel on Sun Mar 31, 2013 7:50 pm; edited 1 time in total (Reason for editing : Correction)
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Re: re: wiring question
by dynchel Sun Mar 31, 2013 7:47 pm
77mali wrote:Did all 73's have points & is that yet another 1 year only 73 thing?
When was the switch to HEI?All gm cars had hei's (and cadalitic converters) for the '75 model year. Some higher end cars (like caddys) got them in '74.
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Re: re: wiring question
by ant7377 Sun Mar 31, 2013 10:11 pm
Call American Auto wire if you need a harness. He has a 73 BB SS Chevelle of his own and knows the car pretty well. You have all you need there though. Alt wire is the same and if you are running HEI already you are good to go.
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Re: re: wiring question
by alleyball4 Sun Mar 31, 2013 11:41 pm
how much are the M and H, and the American Autowire
on my resto-mod car, I went with an EZ Wiring harness. It had tiny writing on the wires, to identify what each wire was. The problem was, my eyes weren't as good as I thought they were, it was so small, the lighting has to be good, and your eyes have to be 20/10 to be able to read them .. lol
I will make some calls, tomorrow, and see what they say. On the SS, I want to stay closer to stock, even though, that's not something you would easily see.
I know rewiring my other car, took me a few weeks to do, so it wasn't as EZ, as they make it sound ... lol
on my resto-mod car, I went with an EZ Wiring harness. It had tiny writing on the wires, to identify what each wire was. The problem was, my eyes weren't as good as I thought they were, it was so small, the lighting has to be good, and your eyes have to be 20/10 to be able to read them .. lol
I will make some calls, tomorrow, and see what they say. On the SS, I want to stay closer to stock, even though, that's not something you would easily see.
I know rewiring my other car, took me a few weeks to do, so it wasn't as EZ, as they make it sound ... lol
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Re: re: wiring question
by dynchel Mon Apr 01, 2013 6:42 am
When I bought the under hood harness (about 4 years ago) I paid $150.00. They claimed it to be restoration correct.
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Re: re: wiring question
by thatfnthing Mon Apr 01, 2013 9:46 am
Keep in mind, though, you're paying largely for convenience. Its maybe $20.00 in actual wire & parts. Everything you need can be obtained via ebay and places like Waytek and Mouser, but then again I actually enjoy that kind of puzzle. 
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G3GM :: G3 Tech :: Electrical
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