Outback ExtremeAire compressor. Mine is mounted on the frame just forward of the battery boxes - from there it goes to a relay mounted about 6" forward of that - then power routes to the Air compressor.
Do you have an air compressor mounted underneath? If not, it may have quit on the previous owner and they just pulled it.
About 2yrs ago (I think) I replaced the Pressure Switch, Relay, and Circuit Breaker because my compressor stopped working, At first I thought I fried the compressor by drowning it in high water...but after hooking jumper cables to it she started right up. I didn't want to go through these three components to decipher which was the culprit so just changes all three out and it has run great since.
EDIT: They have the 30, 40, 50. and 80amp listed on their site
https://www.extremeoutback.com/produ...c-accessories/