Chris said it, CON = Continous Starter solenoids are rated for like 30 seconds, try to hold them connected for 30 mintues bad things happen.
You can replace that 22 year old isolator with many isolator relays you can get at most any RV store If the vehicle is a motor home you can even upgrade to a bi-directional isolator (though that takes a bit more work)
A bi-directional lets the house converter charge the chassis battery when you have power to the house 120 system. Many models out there so I can not recommend one over another.. Just visit your RV store parts counter.