Welcome to BGW.
You've got two issues. SOC (State of Charge) Meter inaccurate and Charger/Cart interface getting hot. And maybe some other stuff too.
First, the SOC issue.
Attached is a Battery Voltage/Specific Gravity table.
Measure the Battery Pack voltage with a DVM.
Find that voltage on the chart.
That is the percentage of charge your SOC Meter should read.
If not, it needs to be reset or replaced.
If replacing, there are dash mounted DVMs available that give you actual battery voltage rather than a LED bargraph or a analog green/yellow/red scale.
Also to get accurate fully charged (100%) battery pack and individual battery voltage readings, wait 12 hours after the charger turns off automatically, or drive cart about a mile, before taking the readings. The batteries will have a "Surface Charge" that dissipates rapidly right after they come off charge. You need to get passed it to get an accurate SOC reading.
Note: Always let the charger turn off automatically, do not stop mid-cycle.
The charger/cart Plug/Receptacle getting hot.
They might get warm over several hours of charging, but they shouldn't get hot in a matter of minutes.
Heat is developed when current passes through a resistance. If you've got heat, you've got resistance. It's as simple as that.
You mentioned cleaning the male and female connectors with a wire wheel. What, if anything, did you use to clean the
inside of the female connector? That is where the electrical interface of the female connector is.
To check the Plug/Receptacle connection:
Using a DVM, measure the voltage across each connection while the battery is being charged. It should be Zero, or very close to it.
Or if the connect is getting hot rapidly, remove the wires from the charger receptacle from the battery and make sure the Charger is unplugged from the AC outlet and measure each connection with an ohmmeter. IT should be Zero Ohms.
If the connections cannot be cleaned or tightened enough to get Zero Volts across them, they'll have to be replaced, otherwise you've got a fire hazard.
Hope this helps,
John