Safety relay which connects to alternator,starter relay, key switch,ground and controller.via wires. What is the function of this kind of a safety relay.
On the safety relays I've run across, it's usually a neutral switch ensuring it's in neutral before it will crank, also a few seat relays to make sure you're in the seat or one on the parking brake. A few others I can't remember now, but all things to keep someone from starting one and it doing something unintended or unsafe. If possible look in the service manual in the wiring diagrams tracing the starting path, finding where relays are located. From that if you have access to trace wires, you might be able to test and see if any of these are not functioning. Usually on old equipment they just get bypassed.
The safety relays on the engine starting systems prevent engaging the starter while the engine is running. Those type of systems showed up with the Japanese excavators being exported all over the world. The safety switches for the hydraulic controls generally prevent movement of the machine when the operator is entering or exiting the cab. I've seen clothes get tangled in the left hand control levers many times.