That circuit gets its power from the ignition switch up under the dash. Could be a loose or dirty connection on the ignition switch, or it could possibly be a broken contact in the back of the fuse box itself. And that requires the tedious task of removing the fuse box from the firewall and replacing the connector and or wire.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...