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Old 08-05-2010, 10:35 AM
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Resistance Wire

My Vette Has Been Changed From Points To Hei. Whoever Made The Change Fired The Hei From The Resistance Wire And Just Jammed It Into The Batt Terminal On The Hei. This Is A 1971 Vette Small Block. I Have Changed Several Points To Hei In The Past And Know This Won't Work Very Well. This Wire Seems To Have Come From The R Terminal On The Starter And Has A Black Factory Looking Wire Hooked To It. Does This Piggybacked Wire Go To Ign? Also My First Attempt To Hook The Batt. Wire From The Hei To Assy. Terminal Was Hot Only When Turned To On And Run. Seems I Ran Into This Problem About 25 Years Ago. Corrected It By Finding A Hot In Run And Start. Thanks In Advance.

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Old 08-05-2010, 05:44 PM
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HEI likes 12 volts minimum. Less voltage can and will take out the module. mount a relay on the firewall. feed the relay with a fused battery wireto #30 terminal and #87 to the BAT on the HEI.use your ignition hot wire to activate relay #85 and ground #86 . Key on supplies HEI with power in run and crank.
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Old 08-06-2010, 10:33 AM
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Resistance Wire

Thank You Very Much Doc.
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Old 08-06-2010, 12:41 PM
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There is a reason the resistance wire is used, it is there so the voltage remains the same when running or cranking. When the starter is engaged the entire system voltage drops due to starter motor load to about 8 or 9 volts or even lower when the weather is cold, it then jumps back to full voltage when the key is released. If the system were optimized to operate on full voltage (12) it would be getting a low voltage (8 or 9) just when it needed full voltage the most during starting-especially in freezing weather. If the system is optimized to run efficiently at 8 or 9 volts then running straight 12 volts presents an overload so either a resister wire or a separate resistor is utilized to drop the voltage during run to about what it would be when the starter is engaged. Then during cranking when the system is under starter motor load a by-pass wire runs to the ignition that is hot ONLY during cranking and this wire by-passes the resistor circuit delivering full system voltage (which is only 8 or 9 volts under starter load) during start. Looking at a schematic should tell you how the by-pass is done with your system but regardless there should be a voltage supply from the ignition in "run" and one that is hot only during "start". This is the reason vehicles with a conventional coil only have 8 or 9 volts on the coil "hot" wire regardless whether it is solid state or point type ignition.
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Old 08-06-2010, 12:59 PM
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If yor running a HEI why not replace the resistance wire from the fuse block connector on the fire wall to the HEI and be done with it.
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Old 08-06-2010, 01:20 PM
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For whatever reason the option to edit a post is not working right now,

I mistakenly said that a full 12 volts presents an overload but that should have been an overvoltage. Not sure how the start voltage drop is dealt with on an HEI system since I deal mostly with Fords but a look at a schematic should reveal the proper connections, Ford or GM the the start voltage drop function is the same and should be dealt with for a proper hook up.
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Old 08-07-2010, 08:59 AM
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If you have less than 12 volts to that HEI, you WILL take out that module. Points systems will burn up the contacts with a full 12 volts, when running. 12 volts at start up was used to give the system a boost to start and knocked down to 6 volts to extend life to the contacts. running the HEI with the resistance wire will result in a no start and a trip to the parts store.
HEI REQUIRES MINIMUM 12 VOLTS AT ALL TIMES............MRTS33 is correct, you canreplace the resistance wire or ballast. A relay supplied system will gaurentee 12 volts to HEI if system is taxed by other loads such as lights, heater, etc.
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Old 08-07-2010, 11:11 AM
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There should be 2 smaller wires on the starter.
PPL is the one that energizes the starter solenoid & starter
Should be marked 'sol'

Another yellow? wire runs from the (IGN??) post and back up to the coil.
This is what provides a full 12v to the coil during cranking only.
(connects battery to to coil only when the starter is engaged)

You can---after changing the resistor wire --- splice this yellow wire
to the at least 12ga ignition wire feeding the HEI.

Some GM ignition switches do NOT provide ignition power while in the "START" mode, this is why an additional wire may be needed.
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Old 08-07-2010, 04:02 PM
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DC, points had noting at all to do with the voltage drop and in fact lower voltage would burn points faster than high voltage, AMPs burn the points not voltage and AMPs increase as voltage drops. Beside how do you explain why the voltage dropping resistance circuit is used many years after points were discontinued? A quick look at a manual for a later model with solid state ignition will show a voltage of 8 to 9 volts at the coil when checking the ignition with the key in run. If voltage is above this value then the manual instructs to check the resistance circuit and this is many years after points became history. Think about it, what happens when the starter engages? The voltage drops drastically to about as little as 8 volts so what happens to an ignition that is optimized for 12 volts? It would be getting a low voltage just when it needs full voltage the most! If the ignition coil were optimized for 8 volts and just one 12 volt wire is used then voltage would be ok at start up but would increase to 12 volts when the key is released. Luckily for us the engineers at the auto factories noticed this little problem and so coils were optimized to run on 8 to 9 volts with the resistance circuit dropping the voltage to this range during run. The by pass circuit is then used ONLY during start so that the resistance circuit would be by passed and voltage would not drop even further. Thus with separate run and start wires, with the run having resistance and the start by passing the run, the voltage to the coil remains the same in start or run. THAT is what the resistance circuit is for and it has absolutely nothing to do with burning points (or static in the radio as I have heard some argue ). I am not sure how the HEI system deals with this, probably similar to how Ford does it with the TFI module which does not require a separate resister but still requires both wires, one hot always in run and the other hot only during cranking. Any way you look at it if only one circuit is used then a system optimized for 12 volts will get a weak voltage at start up and a system optimized for 8 to 9 volts would get an over voltage during run. System voltage WILL drop when the starter is engaged and the resistance circuit is the only way around this.
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Old 08-07-2010, 08:15 PM
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when the coil discharges, where do you think it sends its load through.......I respectfully disagree with you on your understanding of the points ignition system and the GM HEI systems. what we're simply trying to do here is to suggest a way for his system to operate without problems and to make it simple. I only know what has worked for me and many of our racing oriented customers.
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Old 08-07-2010, 09:19 PM
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Sometimes simple works and sometimes it does not work so good, just because it runs ok does not necessarily mean it is running at it's best. Aftermarket ignition manufacturers usually opt for simple installations and it works for them because it is optimized for being simple to install, an example would be an aftermarket high performance coil that has instructions for a one wire hookup. In that case the manufacturer opts for a true 12 volt coil wound so that it functions with a full 12 volts in run and being an enhanced performance unit, plus they are assuming it is going to be installed on a highly tuned engine, it would rarely present a problem with the voltage drop at start up even with the slightly weaker spark from this lower voltage-the same may not work so well with factory parts. I have run into this several times on older Mustangs where "upgraded" later model ignition systems were used and the resistance by pass circuit was omitted, ran fine but often would be a bear to start. Sometimes depending on the system no external resistance is required and the solid state ignition takes care of the voltage drop but it still requires two wires-one hot in "run" and one hot only in "start". An example would be some Ford ignitions where they once used the starter relay (solenoid) to provide a terminal for the hot-in-start wire (resistance by pass) but this was latter dropped in favor of running the wire to the TFI module on the distributor along with the "run" wire, it was eliminated from the solenoid but it is still in the system and still serves the same purpose many years after points were eliminated. On an HEI system that has a hot connection in start, either from the key switch or the starter, eliminating this wire and just running one hot wire will allow the engine to run just fine but could result in a weaker spark at start up.

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Originally Posted by DOCTOR DC
when the coil discharges, where do you think it sends its load through.......
Not sure I understand what you are asking, you think the coil discharges through the points?

I understand very well how a points system works and have been working with them since the 60's.


The resistance circuit was and is used to maintain a stable voltage to the ignition system during the start up voltage drop and point life has nothing to do with it that is why it continued to be used after points faded into history. Besides as I said before AMPs burns points not voltage and lower voltage would present a bigger burn problem than higher voltage because to get the same amount of energy with lower voltage would require more AMPs. My point is that IF the HEI system the OP is asking about had a bypass wire, either from the ignition switch or the starter, then using a relay to eliminate this wire may not work so well, the factory uses that circuit for a purpose and preventing burned points is not that purpose!

Last edited by oldred; 08-07-2010 at 09:30 PM.
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Old 08-07-2010, 10:55 PM
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I beg to differ with you Oldred, in an OEM GM HEI system there is no resistance wire, no start bypass circuit, and they need battery voltage or more to operate most efficiently. If you notice, in a GM HEI system, the positive wire to the coil is always a pink 10 gauge, no resistance there,
At less than 13.2 volts, they will begin to miss under full throttle (maximum spark KV demand) conditions.
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Old 08-08-2010, 06:13 AM
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Yep Oldred, Rick and Doc are correct on the HEI and the voltage it needs. Factory GM cars with HEI do not have a resistance circuit, only the older points cars do.
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Old 08-08-2010, 09:31 AM
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Go back and read what I said, I said IF and made IF quite plain, the HEI system in question used a separate wire then it should not be eliminated. my point is that most systems do use this circuit to deal with the start up voltage drop and to eliminate this wire can cause problems. I brought this up because I have seen it happen more than once (not with an HEI however) and eliminating this circuit in the mistaken belief that it is not needed on any system that does not use points has caused a lot of people problems. I was simply explaining why the resistance circuit was used in the first place and why it should not be automatically just discarded with an ignition upgrade unless that ignition is actually designed to operate on just one wire, which that HEI may very well be. I was then "corrected" and told I was wrong and that the resistance wire was only used to prevent point burn and that simply is not true, as evidenced by the fact that the resistance circuit was/is used many years after points were eliminated.
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Old 08-08-2010, 09:37 AM
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But not on the system the OP is asking about, apples and oranges,
Lower voltage on an HEI system will get you misfires and fried modules.
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