That's not how she was originally built, she used to have 2 fuel cut off solenoids, 1 on each tank, there were 2 switches in the centre console & a couple of LED's to tell you what was open. They were powered by the ignition but you could switch them both off, so the only fuel she had was what was in the carb. You could run on one tank until it went dry then flick the switch to bring the other tank in, you then had option to run for 5 minutes, then shut one of the valves again so you could run again until dry this meant you had just over 5 litres across both tanks left so go looking for a petrol station. Also meant when you were filling the tanks the valves were shut so no fuel was equalising. But I suspect the Birmingham butcher removed them.
Alan...