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MGB 1979 MGB coil w/ altered wiring

wingsandwheels

Senior Member
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Hi All, want to confirm my understanding of the late MGB ignition and what coil I should be using. Interestingly I've found two different wiring diagrams for this car.

My new to me '79 has the original electronic ignition (external amplifier) but with the resistor wire and ballast resistor bypassed resulting in the coil getting the full ~14+ volts running. The coil is a 16c6 which is a 6 volt coil. I cannot (yet....haven't started unwrapping the blue tape) find the ~9v feed from the resistor wire from the main harness.

My inclination is to return the car to its original spec, figure the engineers had some good reason for what they did, but it is running so well that I am a bit hesitant to change anything. The engine was 'detoxed' by the PO's mechanic. I'd say DPO, but the work and the wiring changes appear to be carefully if not well done:D

My questions are:
Assuming I don't return it to original spec:
-Should I run a '12v' internally ballasted coil such as a Lucas DLB101 or Bosch Blue. Can't see the original coil taking full voltage, but it has lasted so far...
-do I need to run a resistor to the feed to the ignition amplifier? Seems to be getting full system voltage.
-any other thoughts


Thanks all.
 

bob67bgt

Jedi Knight
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I do not mess with later MGBs but the earlier ones like my 74 have a resistor wire that runs to the front of the car and then back if I recall correct. I do not think you will find a "normal" resistor for the ignition system on your car. Hope this helps!
Bob
 

Joe Reed

Jedi Warrior
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Do you have two white/green wires attached to the coil? If so, one is the resistor wire and the other is the feed direct from the starer solenoid...
 
OP
wingsandwheels

wingsandwheels

Senior Member
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Do you have two white/green wires attached to the coil? If so, one is the resistor wire and the other is the feed direct from the starer solenoid...
Hi Joe, no, that feed is tied away, there is a white feed to the coil and a white feed from the coil to the amplifier. If one of the w/g wires is the resistor and the other is full 12 during starting, I should be able to test that. Odd, the resistor wire on my tr is a large pink wire. Thanks.
w
 

The Green Hawk

Freshman Member
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I am currently researching the same ignition unknowns on my car!! Like so many times before, establishing what came on the car originally is half the battle.
I agree with you that the factory setup is the preferred setup......especially with the distributor and ignition systems

Please take a look at the link, I have shared it before but find it a great resource for HEI and CEI distributors
https://worldphaco.net/uploads/CUSTOMISING_A_RELUCTOR_STYLE_DISTRIBUTOR.pdf

Peace
 

JPSmit

Moderator
Staff member
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The only thing I would point out, and I think we are talking about the same thing is, having an internal ballast wire is IMHO a bad idea. Our cars (and their wiring) are 40+ years olds, and having a wire in the harness providing resistance and therefore heat cannot end well. With my Vauxhall I have cut out the ballast wire for safety reasons. While origonality is great, upgrades for safety especially are just common sense.
 
OP
wingsandwheels

wingsandwheels

Senior Member
Offline
The only thing I would point out, and I think we are talking about the same thing is, having an internal ballast wire is IMHO a bad idea. Our cars (and their wiring) are 40+ years olds, and having a wire in the harness providing resistance and therefore heat cannot end well. With my Vauxhall I have cut out the ballast wire for safety reasons. While origonality is great, upgrades for safety especially are just common sense.

That thought did cross my mind...especially given how crispy the ballast wire appears on my low mile TR6.

So, as best as I can determine, my car originally had an Opus system that was replaced with the later Lucas system w/ separate amplifier. My current thinking is to bypass the ballast wire and get the proper, internally ballasted coil (effectively back dating the car's set up...essentially the same as my '72 Rover w/ Pertronix).

At this point is my question is does the power feed to the amplifier need to run through the ballast resistor (the OE aluminum finned one) or can it take straight 12v? It is currently getting (and appears to have been for some time) straight 12v and running well........

thanks again all
 
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