65 Impala points to HEI conversion? - Impala Tech
Electrical & Wiring Troubleshooting electrical problems

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post #1 of 12 (permalink) Old 10-29-2016, 09:45 AM Thread Starter
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65 Impala points to HEI conversion?

Been rebuilding my car for a while and almost ready to try to fire it up. I decided to go to the summit ready to run distributor along with the recommended coil. It appears to be fairly straight forward but I was talking to someone and was told I better rewire the original harness with a heavier gauge ignition wire both under hood and under the dash? I'm sure this is this is a fairly common swap and wondering if anyone has had to rewire theirs or any opinions on this?
Thanks
Jim
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post #2 of 12 (permalink) Old 10-29-2016, 12:48 PM
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Following this as we have the HEI for ours ready to go. Just need to do it.
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post #3 of 12 (permalink) Old 10-29-2016, 01:46 PM Thread Starter
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I've found a bit of info so faron another site. They were pulling a new 12ga wire from the fire wall and replacing the old white fabric wrapped 20ga one that went to the positive side of the coil. I also see that the other wire that ran from the + side of the coil to the starter was eliminated.
I've torn apart my wire harness again and thought I would wait a bit to see of anyone else can add to this?
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Last edited by 65 Impaula; 10-29-2016 at 02:32 PM.
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post #4 of 12 (permalink) Old 10-29-2016, 02:50 PM
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When converting from a points distributor to an HEI you do replace some of the factory wiring. This is because the factory used a nickel-chromium (Ni-Chrome) wire to drop the voltage to the points from 12 volts to only 8 volts. The resistor wire was added into the ignition circuit to prolong the points life span.

On the other side of the wiring harness under the hood is a wire that runs up from the starter solenoid to provide full voltage (usually only eight volts due to the draw of the starter engaging drawing a lot of the batteries current) that powered the ignition while the starter is running. This made for easier starts as low voltage to the points results in a weak spark.

You can use a regular length of automotive 14 gage copper wire to replace the twenty or so inches of Ni-Chrome wire in your wiring harness to feed the HEI the full 12 volts nominal current it wants. It will drop the 12 volts nominal (usually about 13.6 when running) down to 4.7 volts by way of resisters inside the HEI module as with most transistors they operate between one to five volts. If you retained the piece of factory resistor wire combined with the resistors in the HEI module voltage would drop too far down to allow the module to operate as designed.

You don't need a 12 gage wire (won't hurt just a tad over kill for the load). The factory used an 18 gage wire which isn't heavy enough in my opinion for the load or to resist breaking from vibrations over time. I like 14 gage wire as it is a happy medium for that Goldilocks moment in terms of reliability and function.

Big Dave
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post #5 of 12 (permalink) Old 10-29-2016, 04:59 PM Thread Starter
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Thanks big Dave! I kinda thought the 12 was a bit too much also but since I just finished running it I'll leave it. Kind of a pain to pull the old wire and trying to get the pin apart at the block but what else am I going to do on a rainy Saturday?
So would you agree then that you can do away with the second wire running from the + side of the coil to the starter? Right now I only have the purple and red running to it now.
Thanks again Dave you are always a big help!

Last edited by 65 Impaula; 10-29-2016 at 05:49 PM.
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post #6 of 12 (permalink) Old 10-29-2016, 06:48 PM
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You can leave it as it won't hurt the operation of the HEI and is a good diagnostic tool for a bad switch that will energize a starter (motor cranks up and runs) but dies when you move the switch from start to run.

That little bit of wire isn't that heavy. But on a true race car you would yank it as every one hundred pounds of weight you loose you lower your elapsed time by a tenth of a second.

Big Dave
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post #7 of 12 (permalink) Old 10-29-2016, 07:00 PM Thread Starter
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Great point but.....it's already been removed.
Thanks again Dave!
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post #8 of 12 (permalink) Old 10-29-2016, 08:59 PM Thread Starter
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Dave if you are still around maybe you can help on 2 more questions.

Should I be concerned with running a heavier wire from the key switch to the fuse box also?

Just to clarify do I need to run a jumper wire from the R side of the starter and tie into the wire I replaced from the fuse box to the coil? I read some other posts around and some say yes others no. It seems like maybe it depends on the type of distributor/coil that's being used?
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post #9 of 12 (permalink) Old 10-30-2016, 07:43 AM
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One word of caution here: If your car was a 396, it came with a ceramic resistor block on the firewall ILO the resistor wire. So it needs to go, but you still need a heavier wire.

Mike

1965 Impala SS 396
1967 SS427
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post #10 of 12 (permalink) Old 10-30-2016, 08:37 AM Thread Starter
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I wish Michael. Mine is a 327 nut I appreciate your input
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post #11 of 12 (permalink) Old 10-30-2016, 11:48 AM
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A heavier gage wire works the same as a lighter gage wire it is just able to carry more current over any given distance. The longer the given distance (say a battery in the trunk), requires an increase in the wire gage to counter the added resistance of the longer wire.

Only down side is because a heavier gage wire is made of expensive copper, it costs more per foot than a lighter gage wire, and as I said above it does add weight.

An HEI distributor doesn't need any wires to be run from the starter solenoid. A heavier gage wire from the fuse box to the ignition key is a plus, but you are still relying upon the fire wall forward stock wiring to power the fuse box. So you don't gain anything until that feed wire is upgraded.

Big Dave
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post #12 of 12 (permalink) Old 10-30-2016, 04:06 PM Thread Starter
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Makes sense. I ran all new wiring from the firewall forward in the engine compartment. I think some snowy winter day I will probably do from the firewall back to the ignition to be safe.
Thanks again!
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