caterpiller man

Hi everyone. I have trojan 124a serial number 61-1084 that has not been started in about 5 years.
It has a diesel engine. The engine is not a cat nor a detroit. I don't if it is a positive or negative ground.

Someone told me it has a voltage reducer. The electrical system is 24 volts. How can I tell if the voltage reducer is functioning.

Any assistance would be greatly appreciated.

Thanks in advance.
Don McHattie
Casper Wyoming