STOPLIGHTS DO NOT WORK-continued

TM 9-2320-279-20-1

Troubleshooting Malfunctions (Cont)

Table 2-9.

Troubleshooting (Cont)

Malfunction

Test or Inspection

Corrective Action

ELECTRICAL SYSTEM (CONT)

7. STOPLIGHTS DO NOT WORK (CONT).

Step 3.

Check for defective service brake stoplight switches. Start engine, build air pressure up to

100 to 120 psi (690 to 827 kPa). Shut off engine. Remove wires from service brake stoplight

switches. Press on brake pedal, check for continuity of service brake stoplight switches.

If no continuity, replace service brake stoplight switch(es) (para 7-46).

If continuity, go to Step 6.

Step 4.

Check for defective trailer hand brake stoplight switch. Start engine, build air pressure up

to 100 to 120 psi (690 to 827 kPa). Shut off engine. Remove wires from trailer hand brake

stoplight switch. Apply trailer hand brake, check for continuity at trailer hand brake stop-

light switch.

If no continuity is found, replace trailer hand brake stoplight switch (para 11-20).

If continuity, go to Step 6.

NOTE

Disabled vehicle's electrical system must be operational in order for stoplights to work.

Step 5.

Check for defective emergency tow stoplight switch. Hook up disabled vehicle correctly to

air lines and charge trailer air system. Remove wires from emergency tow stoplight switch.

Press on brake pedal on tow vehicle, check for continuity at emergency tow stoplight switch

on disabled vehicle.

If no continuity is found, replace emergency tow stoplight switch (para 11-14).

If continuity, go to Step 6.

Step 6.

Check for defective turn signal switch. Disconnect batteries (para 7-91). Disconnect wires

294, 003, and 004 from turn signal switch (para 7-50). With turn signal switch in neutral,

check for continuity between wire 294 (switch side) and 003 (switch side). With turn signal

switch in neutral, check for continuity between wire 294 (switch side) and 004 (switch side).

If no continuity is found, replace turn signal switch (para 7-50).

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