Practically Classics Forum

Hi,
After starting my mgb, the ignition light stayed on. Any ideas how to sort this. Tried starting it again thus morning expecting batteries to be flat, but all started well. It's a late 67 gt

A battery will start and run the car for quite a long time before it goes flat without charging. If you have a multi meter, put it across the terminals on your battery with the engine running and see how many volts it shows. A healthy charging voltage is 13.8. If you are seeing less than 13 with the engine running then you have a problem with your charging circuit. this can be a bad earth on the alternator, a bad connection to the main cable or a fault in the exciter circuit.
You need to test the voltage at the main and exciter terminals on the alternator to be sure of the exact fault. I am not sure how the charge warning light on an MGB is wired but unless you have good reason not to trust it, it is probable that the alternator is no longer charging and needs to be overhauled / replaced.

Would a '67 car have an alternator? I would expect to see a dynamo with an RB340 control box.

Fair point, Whenever I have had a car with a dynamo, it is one of the first things to replace.
It is possible to adjust a voltage regulator and I know there are members who will know how to test and adjust them. You can still test the output from the dynamo itself to ensure it is producing voltage but when it comes to voltage regulators, I have only attempted to adjust one once, 5 hours later I went out and bought an alternator.

Regulators rarely need adjusting. If they give trouble, it is usually contacts dirty and these can be fixed with a gentle clean. Usual suspects would be brushes or wiring. Easy to fix.