terry wrote:

Don't think the OP has a very good appreciation of the issues,
technical and legal liabilities involved; even if the arrangement (of
a previous owner) previously seemed to work OK!

It does 'sound' as though the generator output has; live (red), live
(black, neutral (white), and should have a green ground wire. Any of
those missing, then potentially unsafe and/or could cause damage to
house appliances!!!

Utility workers working on 'downed' lines during/after an emergency
can and understand , HAVE, received fatal electric shocks from line
which they understood were disconnected; by 'back feeds' from
negligent homeowners using improperly connected generators!

That's a possibility, yet I wonder who's making the bigger mistake: the
homeowner who doesn't know any better or the professional lineman who
should.

I'd think any lineman who treats a downed power line as "dead" will end up
that way himself.