MG Car Repair: 1971 MG Midget, positive earth, negative earth

Question
I have not used my '71 Midget in about five years.  I removed the old battery, and (I thought) took careful notice that the system was positive grounded.  I installed a new battery and hooked up the positive ground, and when I did so a good spark arced from the battery post to the connector, and the generator began to smoke.  I ordered a replacement generator, but am afraid that if I hook it up, I'll blow the new generator.  Maybe I made a mistake, and the system is negative ground.  Is there a way to confirm whether the system is positive or negative grounded?
Thanks in advance

Answer
Hi Robert,
All 71 Midgets were negative earth. However, the cars with generators could be changed, but I can't think of any reason why anyone would change a negative earth to a positive earth. I changed many older positive earth MGs to negative earth because the owner wanted to install a high end domestic radio or in a few cases they wanted to install an alternator in place of the generator.

All alternators must be negative earth and generators can be changed with a procedure.

The only reason I can think of why a generator would smoke is if you started the engine with the polarity backwards. Or a regulator was bad which would have caused the generator to smoke no matter what polarity it was. If your regulator had one set of points burned closed when you connect a battery to the system (in either polarity) it would have powered up the generator and if that generator was not turning it would have smoked the large brown wire going to the generator and the generator too.

Other components on the car require a certain polarity. The ignition coil is one, the heater fan motor will blow in either direction but not as well in the wrong direction. Some wiper motors had a cancel device that did not work well backwards. Some aftermarket fuel pumps would not run backwards, the original SU pump would run in either polarity.

Howard