most is grounds related and not that bad. after 30 years of existence a bunch of... inadequacies have popped up in the wiring.
I added her to the registry:
it's a utah truck. the usual things (rust) aren't as much of a concern for you guys. the basic used-car items apply. look for hacked up wiring or other PO shenanigans, make sure you bring it up to operating temp, take it for a test drive, etc.
pop the oil filler cap and peek at the insides. at 300k I'd assume it was well maintained, but that doesn't mean it's had an oil change in the last 30k and the rockers could be caked in sludge. be prepared to start swapping out soft parts and change all the fluids.
found a new-to-me search engine for junkyard Jeeps
https://row52.com/Search/?YMMorVin=YMM&Year=1984-1993&V1=&V2=&V3=&V4=&V5=&V6=&V7=&V8=&V9=&V10=&V11=&V12=&V13=&V14=&V15=&V16=&V17=&ZipCode=&Page=1&ModelId=2938&MakeId=155&LocationId=&IsVin=false&Distance=100
mid 20s around town (lots of hills in this area). but she can still pull the low 30s on highway trips. she's slipped just a little now that she has big tires and 200k.