TM 10-3930-671-24 Table 2-2.  Unit Troubleshooting Procedures - CONT. MALFUNCTION TEST OR INSPECTION CORRECTIVE ACTION ELECTRICAL SYSTEM (CONT.) 36. GAUGES DO NOT OPERATE. Step 1. Check sending unit of malfunctioning gauge (TB ORD 650). If sending unit is faulty, replace sending unit (para 3-22). If sending unit is OK, go to step 2. Step 2. Check continuity of malfunctioning gauge (TB ORD 650). If malfunctioning gauge has no continuity, replace gauge (Para 3-22). If gauge has continuity, notify DS/GS maintenance. 37. COLD START SYSTEM DOES NOT OPERATE. Step 1. Check continuity of glow plug switch wires #22 and #15 (TB ORD 650). If one or more glow plug switch wires have no continuity, notify DS/GS mainte- nance. If glow plug switch wires have continuity, go to step 2. Step 2. Check continuity across glow plug switch (TB ORD 650). If glow plug switch has no continuity, replace switch (Para 3-22). If glow plug switch has continuity, replace glow plugs (Appendix F, Continental Diesel Engine, Section 4.14). 38. HORN DOES NOT OPERATE. Step 1. Check continuity across horn fuse (TB ORD 650). If horn fuse has no continuity, replace horn fuse (Para 3-22). If horn fuse has continuity, go to step 2. Step 2. Check continuity across horn button switch (TB ORD 650). If horn button switch has no continuity, replace horn button switch (Para 3-22). If horn button switch has continuity, go to step 3. 2-25