(1) Loosen screw and disconnect vehicle
harness connector MC18.
(2) Connect a jumperwire between wire
508 at vehicle harness connector
MC18, terminal A, and a known good
(3) Set multimeter select switch to ohms.
(4) Is there continuity between relay R7,
terminal 85 and a known good ground?
(a) If there is no continuity, repair
wire 508 (see schematic Fig 2-38)
or notify DS Maintenance.
(b) If there is continuity, wire 508
(5) Connect vehicle harness connector
MC18 and tighten screw.
(6) Close engine top cover.
Remove all jewelry such as rings, dog tags, bracelets, etc. If jewelry or tools contact positive electrical
circuits, a direct short may result. Damage to equipment, injury or death to personnel may occur.
Circuit breakers CB5, CB6, CB12, CB20, CB22, CB23 and relays R3, R13 - R19, R26, R28, R32, R33
are always electrically hot and can cause severe injury to personnel. Care must be exercised when
working under the electrical circuit board cover
Connector terminals are easily damaged.
Use care when connecting or disconnecting
Relay test must be performed with relay
On DDEC III trucks, wire 988 replaces