Table 4-2. Unit Troubleshooting Procedures (Con't).
TEST OR INSPECTION
Visually check button contacts inside light socket for looseness, corrosion, or other
If button contacts are loose, corroded, or otherwise damaged, replace (see
Use an extension wire, as required, long enough to reach between
Location of connectors will vary with light being checked. If connector is
inside light box at rear of semitrailer, stop/taillight must be removed (see
Trace circuit between button contact at light socket and first connector. Check
continuity in wire between button contact and first connector. Check for a short in
same length of wire. Check for loose, disconnected, or damaged connectors and
If there is continuity, that length of wire is O.K.
If there is no continuity or wire is shorted, replace wire (see paragraphs 4-20,
4-21, 4-24 through 4-26, or 4-28).
Check for continuity and a short in wire between first connector and next connector.
Repeat wire checks until circuit breaker in voltage control unit at front of semitrailer is
reached. Check for loose, disconnected, or damaged connectors and wires.
If there is no continuity, or if wire is shorted, replace wire (see
Check circuit across circuit breaker posts.
If there is continuity, circuit breaker is O.K.
Perform step 7 if affected light operates on circuit breaker #1, #2, #5, #6,
#7, or #8.
Check continuity in wire between circuit breaker post and pin at front of 12-volt
If there is continuity, that wire is O.K.
wire, visually inspect for a bent or corroded connector pin. If pin is damaged,