I am assuming this is 12v lights. Lights can run in daisy chain. The issue can be at adjacent light or overhead fan /break in chain. I had pairs of wire stuffed and crimped one end of butt connector. Some if these just pull right out. Crimp tool and installers hand not strong enough to crush that end.
Also unless you run a ground wire you may not know if you lost ground instead of power.
Some member posted making a plug with wires and battery clamps and use an extension cord. You want an inline fuse in pos wire in that. Now you have you can use male end to test to pos or ground or create another plug with wires , test probes or mini clamps ect. Could also use cig lighter plug might want constant lamp rigged those plugs can be iffy.
Don't forget to mark pos & neg and be careful with power probes so not to fry anything. Powered testing is something I would do for lights ect but not probing unknown plugs pins outs etc.
You can also buy a powered probe tester meter for autos, trucks and forklifts. Still needs good pos & ground. Long ways away in MH. Our old forklift mechanic had one looked super handy I actually forgot about it until just now. You could swap from low impedance voltage tester/ "has some load" testing to powered testing. Now I think I might try to find one.
Here's one that's probably way beyond what's necessary has digital scoping WOW... if you scroll down there's whole bunch similar and cheaper less complicated.
Autel PS100 Power Circuit Probe Kit with 40Ft Cable, 12V 24V Automotive Circuit Tester Electrical System Tool, AC DC Diode Resistance Checker Digital Voltage Tester, Multimeter, Short Finder https://a.co/d/bKQWNXe