My service vehicle soon light won't go off

Fuse. When the fuse blows for the tail-lights, the dash lights go off, they are on the same circuit because otherwise you might be driving around without tail lights and not know it. If it turns out the fuse is blown, and a new fuse immediately blows again, time to start tracing wiring for short. If fuse is OK, if you have a 12V tester, see if you have juice at the tail lights. If so, check ground wires. Also see if there is power on the 'hot' side of the fuse bus...if not, headlight switch may be bad, it is possible for the switch to work for headlights but not make connection for tail/dash.

Which has nothing to do with 'service vehicle' light