It has been stated before without challenge that Hyner did not used to follow the modern trend of re = positive black = negative .
They often used the connections the other way round. Some old vehicles also used + to the chassis _ check the VEHICLE BATTERY with a voltmeter - digital ones are around £10 and IMO no one should contemplate working on a vehicle without using one.
If you have connected the leisure battery the wrong way round the POTENTIAL damage can be extensive BUT the actual damage (if any) needs to be explored by someone who knows what they are looking at and what to check.
Get some help and advice - don't just blunder along thinking you will be OK - you may cause further damage to the vehicle.
Buy a voltmeter URGENTLY.
Thinking of; Mavis, Ray, Sandra and Albert at this time.
Any comments above are only MY OPINION and should be read as that.