No, I checked with the belts loose. Should have taken the belts off shouldn't I :D. I'll check again with the belts off.

I checked the pulleys and they are OK. I tightened the belts. This helped the initial (see below) squeaking. (the belts actually need replacing soon). But the concerning thing is this sudden sound that comes about 20 seconds after start...

Hi. Thanks for that. I'll see what the auto shop has. I'll keep an eye on the ignition switch but it's consistently giving me a reading.

Thanks for this. I tested the relay on the bench, as you suggested. Seemed to work well (ie, activated the higher amp circuit), but not in the vehicle. Swapped another relay in and it worked. Either the original relay is unreliable or...

https://www.12voltplanet.co.uk/relay-guide.html They are pin numbers.

Hi. Latest on my woes! The white cable at the relay IS getting a regular supply of 10.3v every time I turn the ignition to crank. I think my early test must have been a mistake. Testing at the back of the ignition switch also gets 10.30v...