Component Test, Trailer Towing Package Wiring

Backup Lamp Relay

Testing of an ISO relay can be accomplished through the use of three No. 10 (or larger gauge) jumper wires and a Rotunda 73 Digital Multimeter 105-R0051 or equivalent. Remove (unplug) the relay to be tested from the power distribution box, fuse junction panel or individual connector. Using the multimeter, check for continuity between terminal 85 and all other terminals. If resistance is 5 ohms or less between terminal 85 and any other terminal, replace the relay. If resistances are greater than 5 ohms, continue with test.

Using two jumper wires, connect relay terminals 86 and 30 directly to the positive battery terminal. Using the multimeter set in the volts position, check for voltage at terminal 87. If battery voltage is not indicated, replace the relay. If battery voltage is indicated, connect a third jumper wire to terminal 85 and ground the jumper wire to a known good ground. Check for voltage at terminal 87A. If battery voltage is not indicated, replace the relay.