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MG MGB Technical - Bypassing Ballast Resistor for Pertronix Ignitior
|Looking for suggestions for the cleanest looking approach to bypass the ballast resistor on my 79 MGB when I convert over to a pertronix Ignitor II electronic ignition. As I understand it I can get the 12V from either the fuse box or the ignition relay. I can leave the 12V wire coming from the starter solenoid to the coil but need an additional 12 V source for running during non starting conditions. Also what are others doing with the now unused 6V wire from the ballast?|
|Any White wire is switched 12V power from the coil. Tape the 6V wire back to the harness.|
I'm not sure if the II ignition is set up for a non-ballasted coil; and if you are running a non-ballasted coil. If it is, then you don't need the second wire that runs through the ballast resistor (and the resistor for that matter) The hot feed to the coil would then be a switched white wire per FRM.
I'm running one 12 volt battery, and an aftermarket hot coil that is designed to be run with a resistor. I'm only using one feed to the coil (even in starting it's passing through the resistor) and my car fires immediately on the coldest of days. I'm running .050" ++ gap with over 10:1 compression ratio.
With a hot coil and an electronic ignition, the need for the extra coil voltage in starting conditions appears to be a redundancy.
You do need to confirm whether the coil you are using is a coil designed to run on 6 or 12 volts. If it is a coil designed to run behind a resistor, (a 6 volt coil, in effect) then you should not bypass the resistor.
I've run a coil designed for a resistor without a resistor in the feed to the coil. The coil ran too hot to touch but didn't fail. After about a 1,000 miles I went back to the resistor and the coil cooled way down in operation. No apparent difference in performance either way.
|All B with resistor have the resistor incorporated in the harness as a very long high resistance wire - no discrete resistor. The resistor wire is W/LG, visibly connected to a group of W just below the fuse box, going to the LH headlamp harness end as various colored fiberglass braided wire, turning W/LG, then coming back to the distributor. There is a second W/LG which originates at the starter solenoid special terminal to provide 12V on start.|
Any W will provide 12V when the IGN is ON, so both W/LG can be taped back.
All dependent on the coil used and the requirements of the Pertronix unit, as Barry says.
Barry - "coldest of days" indeed!!
When it's a frosty cold morning here in Nor Calif I pull the choke all the way out and it takes 5-10 seconds to fire off.
Thats almost "immediate".
When its a mild day or warmed up it will fire virtually instantly.
I don't think a hotter spark from bypassing the resistor would make a difference.
|How about -20F? I expect them to fire then too - and they do, with or without the ballast stuff. And I expect it to take about 4 revolutions if it's above 0F.|
|Barry and FRM,|
I will be using the coil designed specifically for the Ignitor II. It does require a 12V feed. From reviewing my wiring diagrams for the 79 which original had an Opus electronic ignition there was the ballast resistor feed on one side of the coil and a separate "block type" resistor for the distributor. I am trying to determine which wires I can continue to use to keep things as clean as possible under the hood. I know that one of the white green wires will be 12V from the starter and I can leave this one to the (+) side of the coil. The other is the white green is the wire from the ballast in the loom and will need to be disconnected. I will need a 12V feed to replace this one. I am currently trying to determine if I can leave the two wires currenltly attached to the (-) side of the coil (I believe they are white/black). Both windings in the coil need a 12V feed I assume. I am trying to determine if these are 12V.
|Looked again at the wiring diagram and it appears that I leave both white/black wires as they are: one going to the tachometer and the second the distributor so these should be fine. Trying now to decide on the best place to take the 12V feed for the (+) side of the coil. Fuse box versus ignition relay (?W1 terminal).|
One W/B to the tach stays, the one to the dist is not used - tape it back to the harness. Tape off both W/LG to keep things simple. Remove the finned resistor and tape off those wires. Tape off the whole 3 prong plug. Leave all these in place so it can be changed back or can be figured out by any competent mechanic at a later date.
All you need is one White from any White near the fuse box, or from a W junction point in the harness nearby. Easiest is off the W at the relay, or you can come off the W/N at the relay or fusebox. That goes to coil +. Then the two wires from the Pertronix go to the coil.
Total = 4 wires at the coil,
Coil - gets a W/B, and whatever from the Ignitor
Coil + gets a W and one from Ignitor.
If you are still following this thread...an additional question. If I run a lead straight from the white at the relay will this put additonal current stress (i.e. earlier failure) on the ignition switch itself. And would it therefore be better to take the feed from the W/N at the relay or is this faulty thinking?
|I just bought a pertronix ignition and coil for my stock '66B. I haven't installed one before and haven't looked at it yet.|
Since we're on the subject already and there is good advice flowing is there anything I need to look out for? Does a '66 coil have a ballast resistor? Thank you, -Jeremy
Unless altered by a previous owner the 66 should not have a ballast resistor in the wiring loom. The coil should already be fed with a 12V lead. If you have the Ignitor I you should be able to use your standard coil (3ohm I believe). If you have the ignitor II most recommend purchasing the FlameThrower coil for this ignitor (.6 ohm I believe).
|Yes, W from the W will put the IGN load on the switch, but that's what it's for. It's all the other stuff that overloads it, and the relay feeds all that through the W/N. |
If the relay fails you can still run the car if the fuel pump and IGN are off of the W side.
Another good place to hook in is at the junction of the rear harness with the main harness, just behind & below the fuse box; all you should need is a bullet connector.
Thanks...found the white you are talking about with a four way bullet connector so that indeed would seem ideal as all I will need it a single white wire with a bullet on one end and female spade connector on the other. Thanks again for your help.
This thread was discussed between 06/05/2007 and 10/05/2007
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