Starting motor "click" but not the usual suspects...

Hi all, just got my 79 lightweight S3 (only had it a week) running sweet with clean carb and a filter, only for it to stop starting. Ignition gives a single loud click but doesn't turn.

Battery fully charged and checked. Took off starter, cleaned and checked/replaced. Still the click.

I can spin starter by putting jump lead from pos terminal straight to battery and she fires up fine.

Voltage from battery + to the relay junction (little box with two bolts where all power leads seem to run from) is a bit "iffy" .Jumps from 4v to 7v to 12v then generally holds at 12v ish. Haven't checked cable to starter yet.

Old corroded cables the likely cause?

Cheers

Update, I've just realised the box with two bolts I thought was a relay is the starter solenoid!!!!

Think it's probably the culprit!!!

Yep sticky solinoid. Make sure the inner spring is ok.

I opted for a new one for sake of £15! Will fit it tomorrow! Cheers