A few minutes ago I connected the rig to a dummy load and it works normally..
In the car with the battery, or at home with a power supply? If it messes up in the truck, check the battery voltage at key down when it faults Both with and without a dummy load. Does it NOT fault if you turn the power down?
What kind of antenna are you using in the car and on what bands?
the difference between a dummy load being purely resistive and an antenna that is above that threshold is the resulting difference.
I’m not even going to guess what you are trying to say here.
I think the swr cutback circuit was too sensitive at setting 1..
Maybe, but you said the rig was “shutting down”.This usually means turning itself OFF.
Is the rig in fact turning itself off or is it a power foldback problem?
High SWR foldback does not turn the rig off.
The former sounds like a voltage problem, as has been mentioned, and the latter
sounds like an undetected antenna problem or coax short.
Regardless, you should set the SWR circuit back to the factory default
AND do a microprocessor reset before you proceed any further.
We are thinking the protective system which involves ALC ,output power, and current have grown apart for reasons not fully clear at this time but we need to complete a diagnostics for a more complete view of what is causing this erratic behavior and indeed rf common mode is always a possibility but may be only a minor player with this symptom.
Who is “we”? You have a qualified Tech helping you?
Not sure how circuits “grow apart”.
It’s impossible to even tell what is going on given little information on antenna type, bands used, modes, power levels tried,
power supplies, type of connections, etc…not to mention use of the rambling verbiage.