Original type wiring harness with HEI

[62lwbc10]

Hello all, I am looking to re-wire my 58 using the original type harness that Classic Parts sells for 200 bucks. Im not running any aftermarket electrical stuff (power windows, A/C, rasio, etc), so I figured I would use the original style harness they sell (no fuse box, everything is fused at headlight switch).

I have an updated modern motor with an anternator so they have a version of the harness for this. The thing that is confusing me is the fact that I have an HEI distributor and the harness as-is is meant for a coil type original distributor. What kinds of mods to the harness will be needed to be able to use the new harness with the HEI ignition? I assume its possible since the truck now has the original harness, but the wiring is all homemade and a mess and I cant make heads or tails of it. SInce i have HEI, should I use a mode modern type, fuse block type of harness? Im really hoping to use the original type harness but now am confused. Please let me know your thoughts.

Thanks,
Mark

[NEWFISHER]

Heres a pretty good walk through and a simple solution mabey to your rats nest.
http://www.stovebolt.com/ubbthreads/...72037&page=all

[OrrieG]

Sort of similar, when I put an HEI in my 64 Chevelle I pulled the coil and dist. taped off the original wiring and ran a switched 12v lead to the HEI. It needs to be full 12 volts, I had a switched connection in my stock fuse box I use. 12 GA wire. The other connection on the HEI is for a tach lead. Check the voltage coming off ING 1 on your ingnition switch, it should work.

[NEWFISHER]

When I converted my 55 Chevy wagon to HEI and alternator instead of generator, all of the directions and help always suggested 10 gauge wire to the ignition circuit, don't skimp there.

[1project2many]

Yes, there is reason for using the large gauge wire. As mentioned in the thread linked previously, there's a large "instantaneous" current draw with HEI and using too small a wire will cause the system to suffer. You can, however, install a relay near the distributor to supply power to the HEI. The relay coil will be powered by the original diameter wire from the ignition switch and the relay contacts will use 10 or 12GA wire connected from battery plus to the relay then from relay to HEI. This method is safest as it does not force the ignition switch to handle additional current required for the HEI.

[mr48chev]

I did my 71 GMC exactly the way OrrieG did his truck. It has worked great for two years.
It (the heavy wire to the HEI) does need to be wired into a connection that is hot any time the key.

I chose to tape the original wires back into the harness just like he did because there may come a time when I or someone else wants to put a stock point style distributor back in the truck. A minute or so of unwrapping the tape and it's ready to go in that case.

Make sure that you get the correct wire connector to connect to the HEI so that it doesn't break connection going down the road. I had a regular female slide connector on mine and it would loosen up enough so that if I hit a rough spot of road the engine would sometimes quit. Not fun at 3:30 in the morning on the way to work.

[OrrieG]

I like the relay idea, need to look at my aftermarket harness to see how it is set up.

[1project2many]

Make sure that you get the correct wire connector to connect to the HEI so that it doesn't break connection going down the road. I had a regular female slide connector on mine and it would loosen up enough so that if I hit a rough spot of road the engine would sometimes quit. Not fun at 3:30 in the morning on the way to work.

For many years you could buy the connector through the pars stores. At a minimum you should use the correct style spade terminal. The generic parts store versions are not good at staying put and are not as good with high current. This is the right one:



You should have these around anyway as they match the OE terminals in our trucks.

[_Ogre]

I`ve only done 2 hei conversions, but i just eliminated the resistor and used the stock ignition wire on both

[OrrieG]

I did some looking around, you can get the stock GM HEI replacement socket and pigtail online. I don't know if the aftermarket ones use the same socket, I would assume they would so the aftermarket dist would be a direct replacement without rewiring.

[62lwbc10]

Hey thanks for the feedback. So it seems I will be able to use the new original type harness with the HEI, taking consideration of your suggestions. Just to be clear, this is not a conversion, the truck has the HEI already with a badly molested original harness (that originally had a generator). I now have the HEI and alternator. Let me ask you, its very likely the PO just used the original wire from the harness to power the HEI (I still need to confirm). If this is the case, what issues could I expect? I am having some motor issues and Im now wondering if the issues Im having could be somehow related to issues with the wiring to the HEI. Id be interested to hear your thoughts.

THanks in advance,
Mark

[1project2many]

Depending on what's happening you may have insufficient spark under load or acceleration or it could be as bad as strange running at idle due to very short spark duration (saw that one when HEI was connected to original resistance wire). The majority of conversions done using original gauge wiring don't display any noticeable issues but to me it only makes sense to wire it properly from the beginning rather than have to diagnose a problem after the fact.