On Sat, 9 Mar 2019 08:13:00 -0000, "Brian Gaff"
wrote:

Sounds a bit odd if the lamp and the thermostat are linked. problem waiting
to happen if they rely on a bulb as a ref or something.

I believe many vehicle charging systems relied on the presence of the
ignition lamp to provide excitation to the dynamo (/alternator?).

I know my BMW motorbikes do.

Cheers, T i m