THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

The way I test a Lucas generator in situ is to disconnect the large and small terminal wires, connect a jumper wire from one terminal to the other and a volt meter instrument to that jumper wire and the other voltmeter lead to ground. Start the car and SLOWLY increase engine speed above the idle and you should see a smoothly increasing voltage. Do not exceed 18 volts. If this test is successful, the likely issue is with the regulator or the wiring between the regulator and generator.

Welcome to the forum. Can you put your location in your details please so we know where you are. Helps when suggesting suppliers and you might be around the corner from another S type owner.

Are you still running the original RB340 voltage regulator?

I had a similar problem in fact I have had it twice. The first with the old RB340 which I replaced with a new one and it fixed the problem. Fairly cheap so not worth trying to repair the original. Only £31 from SNG https://www.sngbarratt.com/English/#/UK/parts/8fc02820-9366-4248-aed4-052b18f809c0?fromList=Search%20for%20%60RB340%60

The second was recently, again a drain on the Amp meter and a red light but I have since the first incident changed to a Dynalite alternator. Battery ran out of power as it was not being charged and I could not start the car. Same problem though being the voltage regulator. Changed the regulator in the alternator and problem fixed.

My 1967 3.8S ammeter shows continuously in the Discharge side, and the ignition lamp stays constantly on. This despite a NEW battery at full charge, and generator brushes with lots of life left. I removed and cleaned all voltage regulator leads. Are there readers who have had a similar issue?