melex 252

[quailwood_shop]

Hello to all out there
I have a melex 252 .
the cart was brought to me because the batteries were dead even though they were just replaced , I was told they were installed by a local cart shop and had worked for a while until the lady started to smell burning and she parked it .
I have charged the batteries and I have tested them for surface charge and have tested each cell individually using hydrometer and they are all holding at 6.2 volts . I have checked all connections and all cable's are tight.
but when I hook the batteries up the negative throws a huge spark and the motor begins to run regardless if the key is on or off ? and regardless if the accelerator pedal is being pressed ?it shuts off in neutral. the burning smell is coming from the negative on the last battery in the series .
any help would be much appreciated

[49ford]

I noticed no one posted ideas on this. Did you ever figure this sparkin thing out?