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Old 03-28-2013, 03:11 PM
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Points to HEI

converting a point system to HEI on a 71 chevy pickup. I know that your supposed to bypass the resister wire. The problem I'm having is that when I crank the engine over to find a 12v source I see the whole electrical system drop to 9v. It drops right at the battery? Also, I'm I supposed to take the resistor wire out that goes to the starter and replace it also? Take if off all together? Any help would be greatly appreciated!

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Old 03-28-2013, 05:14 PM
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Cut your harness back to where the resister wire starts...That is your 12 volt source for the distributor.
The reason the voltage drops when you are cranking it is that the starter is taking all the power. When running, it will be 12+ volts
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Old 03-28-2013, 05:40 PM
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Thanks for the info.....My concern was that I was told the HEI would fire at all at 9 volts, and if I'm cranking the engine and I can never find a 12 volt source then it'll never fire. Will it in fact fire at 9 volts when cranking? I do see where the resister wire ends, i'll cut it back to that point and put in new wire....but at that same point there is more resister wire that goes to the starter, do I cut that out also? and leave it off the starter?
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Old 03-28-2013, 06:17 PM
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IMO I'd replace the resistor wire all the way back to the ing switch....... my reasoning..... old wire-new system. It will work just fine by just removing the resistance part tho'

Remove the starter solenoid "I" or "R" terminal wire (non resistance wire) at the starter and off the Pos post of the old coil, it isn't needed.

How the old system worked: When the key was turned to start, the starter solenoid engaged and the "I" terminal went hot and provided a full 12v to the coil to aid the vehicle in starting, when you released the key to the run position, the solenoid dis-engaged and removed the 12v from the coil and the resistance wire provided 9-ish volt to the coil. The coil only needs 9-ish volts to operate properly and if it recieved 12v all the time it would burn up in short order etc.....

The HEI needs 12v constantly, so..... you need to insure your current run wire (old resistance wire) provides 12v while the key is in the start position and in the run position. If it doesn't you can hook back up the "I" terminal wire etc.... or find a wire that does.
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Old 03-28-2013, 09:34 PM
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I had a issue once with a resistor wire - I finally used that wire to turn on a relay - then I had direct power from the battery to the distributor. That worked great.
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Old 03-29-2013, 09:21 AM
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That's what I was going to suggest -- use the ballast wire to trigger a relay. I've done that with both my '70 Caprice and my '71 Thunderbird and they both work great.
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Old 03-29-2013, 09:58 AM
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Leave the resistor wire where it is. Unhook the yellow wire off the starter and the wires off the old coil and tape them all up into the wire harness. You might do a resto some day and want to use them again.
Run a 12 gauge wire from the hei to your fuse box. PLug the wire into a 12v unfused terminal on the box. There should be a couple there.
Time your motor and fire it up.
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Old 03-29-2013, 10:09 AM
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Thanks for the info! one question about the wire going to the starter, would having that hooked up cause a drop in voltage when cranking? I'm just curious about that and what exatly is the purpose of it, if we can run it without it on there? I'll give this a shot tonite, I have a used HEI (never do that again) and I'm having the module and coil tested today to make sure they are good. Anyway, I really appreciate all the help!!
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Old 03-29-2013, 10:33 AM
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If the yellow wire is hooked up it will have 12v in it only when you're cranking the motor. It might make your voltage drop if somewhere in your wiring that yellow wire is grounded.
The yellow wires purpose is to supply 12v to the coil on your points type ignition when starting. When your motor's running the power to the coil comes thru the resistance wire. Reduces the voltage to the coil to 6-7 volts. 12 v to the coil full time overheats it and it melts.
If you unwrap your wiring you'll see where the yellow wire is connected to the resistance wire. You don't need any of the yellow or resistance wire to run your hei. Some people plug in a new wire to the junction box where the resistor wire plugged in, some people prefer to run a new wire all the way to the ignition switch and some do like me. Run a wire to an unfused tang on the fuse box.
Once you get the wiring right to your hei do you know how to time your motor and break it in?
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Old 03-29-2013, 10:58 AM
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Running a wire straight to an "unfused tang" on your fuse box is all well and good, but now you've got an unfused circuit feeding your coil. That's not optimal -- what if there's a short to ground?. The coil draws a fair amount of current.

At least put a fusible link in that wire, at the fuse box end of it. (14-gauge wire, with 18-gauge fusible link would do.)

The benefit of the relay is it delivers full voltage to the coil, not voltage that's been reduced somewhat by the resistance of the ignition switch itself and all the extra wiring to go to and from the switch... That's why many folks run their headlights off relays, to get the maximum voltage and brightness.

You can get these Bosch-style relays for about $5 on Ebay. I think I paid $10 for a pack of 5. You can never have too many, there's always something fun you can do with relays...
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Old 03-29-2013, 11:09 AM
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OOPS!!
Forgot to say I wired a 30 amp inline fuse into my 12v supply wire.
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Old 03-29-2013, 11:45 AM
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Hah -- I made an oops, too. While extolling the virtues of utilizing relays I just remembered that I forgot to wire in a fusible link in my Thunderbird (I did put one in my Caprice). So now I have to remember to go back and do that. "Practice what I preach" and so forth...

Mark Hamilton at MadElectrical.com sings the praises of fusible links -- he prefers them to other types of fuses. Of course, any (properly rated) fuse is better than nothing...
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Old 03-29-2013, 02:52 PM
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Thanks for a the great info! I'll sounds like i need to pull that yellow wire off of the starter....i see where its connected to the coil wire further up in the harness, I found a place on the fuse box that has switched power and it looks like it runs at 12volts when the switch is in the run position but drops to 10.5 during cranking. One thing i did notice when I was testing last nite that no matter where I checked the voltage during the cranking cycle it dropped to about 10.5 volts. Is this gonna cause me an issue with the HEI during start up? ( had the module in the distubutor checked today and it was bad, Im replacing that tonite)
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Old 03-29-2013, 03:03 PM
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I admit I'm not an expert, but keep in mind the starter draws a lot of current, which necessarily depresses the voltage somewhat -- something to do with Ohm's Law. I believe you'd get that kind of voltage even in a perfectly operating system, until the starter disengages, that is. Then it should go back up to 14.2 or whatever (alternator voltage).
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Old 03-29-2013, 04:01 PM
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Once again, thanks everyone for all the great help!! I'll let you know how it turns out.
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