MGB Starting Problems

[HildaBilda]

I am new to the MG scene and my 1979 MGB GT is fighting me all the way to get up and running!!

The Story in this issue is:

- Car was running but lumpy and couldn’t change timing as distributor seized in housing.
- Got it out and saw it was a junk aftermarket piece so binned it and purchased a lovely refurbished 45D from Distributor Doctor.
- Swapped in an electronic ignition module. Popped it into car. Started up first time ran it up to temperature. Set timing - running sweet. All good.
- UNTIL - I simply disconnected timing light from coil and it died!!!! Would kot start again. Starter turning but no spark and now no ignition light on dash.
- Swapped out e-ignition module back to points & condensor. No change.
- No power to coil and no spark! Starter turns but seemingly getting nothing to coil and distributor. And no ignition light on dash.

Any help/ideas would be much appreciated. Teated all connections to starter relay, fuse box and coil. I am stumped for ideas.

What could have gone wrong?

 

[Gliderman8]

Possible bad ignition switch?

 

[mezy]

If the oil light comes on but no ignition light I would say ign switch is ok.
If no lights at all ign switch will need testing with a volt metre.
Is it dynamo or alternator

 

[Sarastro]

There is no reason why disconnecting the timing light should stall the car. So, something must have happened simultaneously. Take a close look at the wiring where the timing light was connected. It's possible that the wire is broken just inside the insulation--this happened to me once--or possibly at the distributor connection. It's also possible that the coil is defective internally, or there is a bad connection. This is probably something simple, so don't start tearing everything apart until you check the simple things.

I suggest using a multimeter to check for voltages at all the important points with the ignition on. Also check the coil primary resistance (between the two low-voltage connection points, with nothing connected.) It should be 3-4 ohms. Wiggle the terminals when you do this, in case it might be intermittent.

In most LBCs, the ignition circuit is not fused; dunno about the 79 BGT. If it is fused, check that. It's really easy to short something, blow a fuse, and not realize it.