Gerry, when it comes to anything electrical
, faulty grounds are usually the hardest thing to find.
If there were multiple faulty grounds, then I can understand the possibility of the furnace
being in and out more than once. Think you found something, repair it, put it back in then find another fault further down the circuit line, remove & repair newly found problem.
Don' forget that a 1980's trailer is now over 25 years old and has seen a lot of condensation in the normal air around it in that length of time, so if you are repaired with just a few ground connections cleaned up, your not doing too badly. It's not unusual to replace 25 year old furnaces at home or in your RV.
Maybe you can drop by and help me trace a couple of electrical
problems on my 31 year old British Sports Car
Some shops that do a very large amount of furnace or gas appliance repair are set up for full bench testing of these appliances, but not many have the space for a dedicated test area so they test the units in place in the trailer etc.