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MG Midget and Sprite Technical - Ballast Resistors

Having spent the last few days engrossed in the wonderful world of ballast resistors i thought i might turn to you guys for a bit of guidance. I have a Lucas DLB105 coil in a midget 1500, there are two wires going into the positive terminal on the coil, both white with a green stripe. My investigations tell me that one of these wires is the ballast resistor. Do i have the right coil fitted? If not, instead of replacing the coil should i just bypass the resistor?


Any help greatly appreciated!
Jamie Watt

The DLB 105 is a high energy 12 volt coil and is not compatable with your ignition wiring.

You need to bypass the existing wiring and wire a direct feed to the coil from the ignition. This will give the coil 12 volts

The wires connected at present give the coil about 8 volts when running and 12 volts during starting.

See here http://is.gd/yAqETw
Robert (Bob) Midget Turbo

Bob's got it... those two wires both feed positive voltage to the coil, BUT - one comes via a resistance wire to provide the reduced voltage Bob mentioned. The other one comes from the starter solenoid and provides a full 12V during cranking - when the engine starts, that one cuts out and the ballasted wire takes over.

Cheers, and best of luck,

-:G:-
Gryf Ketcherside

There's a reason for the lower voltage while the engine is running, less voltage across the points which makes them last longer. If you've fitted an electronic ignition then that feature is not needed and if you have the correct coil you can run a full +12v to the coil.
B Young

There are books with this stuff in..

The DLB105 is a Lucas sports coil not for use with a ballast resistor. If your car has a ballast resistor and you want a Lucas sports coil it's the DLB110 you need. page 52

I don't necessarily disagree with B Young's comments though that isn't my understanding of the benefit of a ballasted coil.


Daniel Thirteen-Twelve

Thanks guys, its an extremely interesting (although confusing) topic. Is it a case of swapping one wire (the one with the ballast resistor) with a new wire or do i need to alter its route in any way?

Im not sure if this will confuse matters or if the two issues are connected but i've also just bought myself a pre-engaged high-torque starter motor from Moss and there appears to be a spade connector on the new motor that isn't on the old one - i don't have a wire for it!
Jamie Watt

This thread was discussed between 15/02/2011 and 17/02/2011

MG Midget and Sprite Technical index

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