Welcome to our Site for MG, Triumph and Austin-Healey Car Information.


MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - Ballast Resistor

My car is a 1975 Early rubber bumper GT .I have converted to 12 volt coil and need to ensure that i have bypassed the ballast resistor.Where exactly is it
and what should i look for?
K.R Jackson


The ballast resister is a piece of iron wire bound up in the wiring harness. On a TR6, it's a pink and white wire, looking somewhat like a shoelace. I assume it's the same on an MGB.

Regardless, it's easy to eliminate. Just run a jumper wire from the white wires on the fuse box to the plus terminal of the coil. You can leave the existing white/light green wires there or pull them off and insulate them, your choice. 16ga wire is adequate for the jumper.
Dan Masters

As Dan says but the pink wire is inside the loom tape so unless you start cutting that you won't see it. It is white at the fusebox end and white/light-blue (if a factory V8) or white/light-green (if originally a 4-cylinder) at the coil +ve and solenoid boost terminal.

But why did you convert from the 6v coil? In most cases that will be a retrograde step.
Paul Hunt

Many thanks for the information on the ballast resistor wiring.When I completed the engine conversion I was using the original SD1 coil and asked my electrician to bypass the ballast resistor.I was not sure he had actually done this hence the questions re the ballast resistor.
Having gone 12v and looked at the advice on the site it seemed that a Lucas 12v sports coil DLB105 was the way to go,it has impressive output throughot the rev range. I had just ordered it 5mins before reading your post, I am now of course wondering if i've done the right thing.
Thanks again,

Kevin Jackson.
K.R Jackson

Kevin, whilst a sport coil has a potentially (ho ho) higher output the actual HT voltage is determined by the plug gap. The 6v coil, ballast and boost circuit can make the difference between starting and not starting under marginal conditions like cold, damp and poor maintenance.
Paul Hunt

Paul,Thanks again for your input,the new coil arrived this AM from BHive excellent service as usual, ordered at 3PM yesterday arrived 10.30 am today, so will try it out, it's got to be better than the original SD1 unit.If starting is still a problem I can always revert to the 6 volt option.

K.R Jackson

This thread was discussed between 21/09/2004 and 23/09/2004

MG MGB GT V8 Factory Originals Technical index

This thread is from the archives. Join the live MG MGB GT V8 Factory Originals Technical BBS now