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MG MGB Technical - ? Starter Wire

Under 1977 B noticed in wiring harness terminating at starter an unattached green and white wire. No prolem starting or anything else just a looose white/green stripe wire terminating with spade it at starter solenoid position what is it anyone now.
Jon L

Jon - Go to http://www.advanceautowire.com/ Click on Stock Schematics and scroll down to MB, MGC, MGBGT then scroll to your car's year. You can print out a color print of your wiring, which should give you an idea of where that wire should go. Cheers - Dave
David DuBois

It was installed to provide 12 volts to the coil when starting engine. This direct connection bypassed the ballast resistance in the wiring. After starting the voltage is removed from the white/light green wire and a reduced voltage is fed to the coil (around 7-8 volts) through the ballast wiring circuit.

Many cars have been modified with the addition of a points type distributor and a coil that doesn't need a ballast resistor, that may have happened to your car.
Clifton Gordon

It is nothing to do with points-type distributors or not. UK cars always had points distributors but all rubber cars had the ballasted ignition systems, as did all North American cars whether with Opus or CEI ignition. The missing wire means that you are starting on reduced voltage, which will probably be OK most of the time, but under adverse conditions can make the difference between starting and not starting.

It's also nothing to do with whether a 12v coil has been fitted or not and the ballast bypassed, in which case the wire does nothing at all connected or not connected, but you still run the risk of not starting under adverse conditions. There is no good reason whatsoever in replacing the 6v coil with a 12v and bypassing the ballast on a rubber bumper, only bad reasons.
Paul Hunt

Paul. "It has nothing to do with points-type distributors or not." True statement, on the face of it. But, not completely true here in the US. Brit-Tek, one of the better sources for MGB parts, sells their "ultimate ignition package" which includes a new Lucas 45D4 distributor (with points, condenser, cap and rotor), spark plug wire set, and a new Lucas Sports Coil. In their instruction sheet for the new system, they include how to wire the system to full time 12V operation to allow the use of the Sports Coil. (I have heard of Sports Coils for use with the standard RB ignition system, but have never seen any available here in the US.)

If one has a points type distributor, there is a very good chance that Brit-Tek was the original source. If one installs the Brit-Tek package, there is a good chance the system will be changed over to full time 12V input as part of the installation.

So, Clifton's linkage of the points type distributor and the conversion to the full time 12V input makes sense from a US perspective--especially on the US east coast where Brit-Tek is located. Even if all three of us understand that the points type distributor will function over a fairly wide range of voltage inputs, being a quite basic switching device, and will work perfectly well with either type of coil.

Les
Les Bengtson

I was only speaking for factory systems, after-market are a whole different ball-game. There are some that use a very low resistance coil in the tenths of an ohm, and in cases like those the coil, trigger and wiring *all* must be to suppliers specs.

I say again that fitting a points-type distributor does *not* automatically demand that you change the coil and wiring. If one chooses to buy and fit a package that *includes* a different coil then that is something else. A point-type distributor is not voltage dependant, it is only a switch. It is the coil that is voltage dependant, and so when changing a coil one has to be sure juist how the existing system has been wired. Going from a 6v coil and ballasted wiring on a rubber bumper car to a 12v coil and unballasted system is a retrograde step.
Paul Hunt

This thread was discussed between 01/08/2008 and 09/08/2008

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