Practically Classics Forum

Hello everyone,
Just drove the Stag over to Robsport, drove home and changed the ignition coil and now I won't start, won't fire at all. I haven't checked for a spark as it got dark, but does the coil body need an earth? Being as the coil is painted black I wasn't sure.
Cheers!
-Peter

No, the coil body doesn't need to be earthed.

JPB wrote:No, the coil body doesn't need to be earthed.

Err - far be it from me to question someone who clearly knows more about electronics than me, but surely it does? How does the HT side complete a circuit? Surely ones side of the secondary coil is the HT king lead, and the other side is the coil body = earth?

OP - do you have the original coil still? I know I'd be changing that back straight away to check it really is a fault isolated to the coil.

Cheers!

The "earth" side of both coils is common.
The following sketch should explain why no can earthing is needed:

Tried the old coil this morning and nothing, sooo i must have touched or knocked something but no idea what it is :S

Thanks John. Never knew that!

Peter - correct, you've somehow introduced the fault when you changed the coil. So, I assume this is still conventional points ignition? In that case, first check all the coil and dizzy connections for soundness. Then go round with a meter and see what's missing. Check the Low Tension side - you have 12V at the + terminal of the coil? If not, trace this back until you do. Then check you have a voltage on the other side of the coil with the points open, and then 0V with them closed - or you could check this side with an ohm-meter for continuity.

A wiring diagram will help here if you're not sure what goes where.

All the best with it!

Ah right forgot to mention it is on lumenition. Yep I have 12v to the + side then the -VE side i have 12v aswell and that has the wire to the lumenition box and 2 other orange wires. is that right? I have 12 volts on the - side when the little disc isn't breaking the signal in the dizzy so is that wrong? Cheers!

It's gone quiet Assuming you still have the problem what about the basics i.e. fuel getting through and spark at the plug are often overlooked.
A very rough and ready but effective method is to remove a plug and set it in it's lead with the plug body in firm contact with the head and then crank the starter - the darker the better and you will see and hear the spark if things are OK.
On fuel - disconnect at the carb inlet and crank if it's a mechanical pump or just switch on if it's electric - keep it brief on the starter or ignition switch as there should be quite a gusher if the pump is healthy.
In the interests of health and safety DO THE IGNITION CHECK FIRST AS RESIDUEL FUEL VAPOUR COULD EXPLODE and have a can to catch the fuel. Also have your garage fire extiguisher handy - you do have one don't you
If both checks are positive it should start and run - simples If it fails either check, go into that system. Of course you could simply have run out of fuel

Connect the amplifier in accordance with the diagram pmd. Without that connected correctly, you'll find that it won't start - no matter what else you do.

Sorted! Lumentition module replaced and now all is good thank you for all your suggestions.