I don't think you need to remove the fender, but you do need to get uo behind/above the inner liner. You can do that by removing the flare (carefully, preceded by lots of PB Blaster, because you're likely to break off most of the little studs), or by popping the plastic barb fittings that hold the liner against the inner fender. You'll need to remove the inner liner to take off the fender anyway, so doing it isn't wasted effort if this doesn't provide sufficient access to reach the wiring.
The fender itself is held with about four bolts on the top, covered by the edge of the hood; two on the bottom just ahead of the door; two from the door post, accessible with the door open; and two (I think) in the front behind the headlight. When I replaced the front fenders on my MJ I recall removing the entire header -- don't remember the details, but I think it was necessary or I sure wouldn't have done it.