Did you snag a set of the manuals and schematics? I'll attach a copy here in case you idn't get your yet.
I assume you're talking about the RUNNING LIGHT circuit, but you didn't specifically say that. And I'm also assuming the ONLY function that's flaky is the running lights. If other functions are flaky such as the turn signals or brake lights, or especially if lights are interacting like the brake lights dim if you also turn on a turn signal, then a bad GROUND is more likely than a bad fuse.
Front fuse #32 feeds the threaded stud that's intended for the red wire ring lug everybody who's a regular reader here or on trailvoy knows about. It's only used for trailers that need a full-time battery recharge feed. Nothing to do with trailer brakes or lighting.
Running lights are fed by the Park Lamp relay, but are fused by REAR fuse 42. That's almost certainly your problem. For completeness, the list is as follows:
- Trailer brake controller feed - front #19
- Red wire trailer battery charge - front #32
- Backup lamps - front #27, then the backup switch on the side of the tranny, then front #4
- Parking and running lamps - Park LP relay, then read #42
- Left brake and turn signal - flasher module, then front #51
- Right brake and turn signal - flasher module, then front $50
