TM   9-2320-273-20 Table  5-7.  Instruments  and  Indicators  Circuit  Troubleshooting. 1 2 3 1 2 3 INSTRUCTION INDICATION YES DIFFERENTIAL    LOCKUP    LAMP    INOPERATIVE. With    differential    lock- up  control  set  to LOCK,  and  ENGINE RUN  switch  ON check  for  voltage  to the lamp using a multi  meter. Attach   test   lead across  the  differential lockup    control terminals. Troubleshoot    wiring. Refer  to  wire  diagram and schematic in Appendix   D. PARK   BRAKE   LAMP With park brake ap- plied  and  ENGINE RUN  switch  set  to ON,  use  a  multimeter to check voItage to the lamp. Attach  test  lead across  park  brake switch   terminals (located   in   instrument panel  near  circuit breaker). Troubleshoot    wiring. Refer  to  wiring  dia- gram and schematic in  Appendix  D. 12  volts  dc  nominal. Lamp  lights. INOPERATIVE. 12  volts  dc  nominal. Lamp  lights. Check  for good ground at bulb. (Replace bulb) (para 5-63). Replace differential lockup  con- trol   (para 5-83). Check for a good  ground at  the  bulb. (Replace  the bulb) (para 5-63). Replace park brake switch (para 5-82). NO Go to Step 2. Go to Step 3. Go to Step 2. Go to Step 3. 5-42 REMARKS