
Holy mother of creeping currents, I hear your knocking
Wow, there is some cleaning and reinsulation needed at least.
personally.. I'd ripp that old mechanical control out and replace it with a more modern PWM controller,
just to be more gentle on the batteries and loose less power on the wiring.
Those 4 speed mechanical resistance controllers are reliable, that's very true.. even more reliable as any MosFet setup could ever be;
but honestly.. you always drain the battery at full rates with a setup like that.
To call it old tech would be an understatement.. that thing (electrically) is ANCIENT!
(looks like it's 1960s rather than 70ies)
And don't get me wrong.. new is not always better.. in fact quite often it's the other way around;
but this... I'd clean it, restore it and put in on a shelf for display (or on ebay for profit)
the motor would be powered by a more recent controller for sure
'sid