Ignition coil swap...

[1TUFMB]

hey guys,
i have recently swapped over my ignition coil in my m/b and can not get it to start i have searched on here and tried several of the recommendations to no success,
i have installed a Bosch GT40R to replace the faulty standard one
the problem im having is that the m/b will crank and sort of start while i have the key turned to start it but once i let go it just dies so its cranking and everything but not kicking over

any help or ideas greatly appreciated

chris

[Brayden]

Sounds like you've got the wiring wrong, or the actual fault isn't with the coil. When replacing the coil its always a good idea to replace the points, plugs and leads too.

[gadj]

Check the ballast resistor. on cranking you have 12V through the coil but when you release the key to 'run' the power takes another circuit through the ballast resistor which drops the voltage somewhere between 7.5 to 10V.
(That is what I remember of it & may be slightly wrong so do further research) The ballast resistor is an oblong ceramic block usually mounted near the coil. The 'R' in GT40R means the coil is to be used with a resistor.

[ToranaGuy]

I thought the mighty boy got 9v when the ignition was in the "on" position?

Anyway, there is a thread on there regarding coil wiring, look & you will find it.

Here's one Coil Wiring Thread

Check your points gap - make sure they are opening properly!

Cheers

ToranaGuy

[1TUFMB]

I have replaced plugs leads points dizzy cap rotor button and theignition coil was the next thing I could think of I go over the wiring again today and thanks for the help so far

[1TUFMB]

afternoon guys,
i have today gone over the wiring time and time again i then tried putting the standard coil back in as it was and does the same thing any other ideas ??

chris

[karlmeredith]

disconnect the ballast resistor and check with multimeter for continuity if none replace it
while cranking it gets bypassed so will seem to start. then die when you release if faulty as the power to the coil has to go through it
also check the spring return in the ignition switch had one years ago (not on a MB but same principle) needs to spring back to run position, but the one i had wasn't quite returning from start to run so no power was getting through.

[1TUFMB]

got my hands on a spare ballist resistor swpped them round and hey presto it starts so im assuming the one i had was either buggered or playing up so yeah all is good now running fine thanks for the help guys

[gadj]

The ballast resistor is the most reliable of electrical faults to diagnose upon failure. Every time you will find the engine starts but as soon as you release the key it dies.