2003 Yukon XL Denali Trailer Light Problems I have a 2003 Yukon XL Denali with the factory installed heavy duty tow package ... but have had trailer light problems for years. A few years ago the lighting control module burned up when I hooked up a new trailer with LED running, break and turn lights. After replacing the module, the lights were fine for this trialer and 2 others until the right turn signal stopped working. Now there''s not even an electrical signal where the fuse plugs into the interior fuse panel. I'd like to address the root cause problem before spending the time and another $100 to replace the lighting module. Any advice is appreciated.

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07 Apr, 2017

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Lighting control module ? ?????? Hazard / flasher module ! Now ( there''s not even an electrical signal where the fuse plugs into the interior fuse panel.) What FUSE ??????

Stop Lamps
The STOP LP 25 A fuse in the underhood fuse block supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery positive voltage is supplied to both the STOP 15 A fuse and the CHMSL 10 A fuse in the I/P fuse block, and to the turn signal/hazard module. The turn signal/hazard module then supplies voltage to both of the trailer rear turn/stop lamp supply voltage circuits. The voltage from the CHMSL 10 A fuse is to the center high mounted stop lamp (CHMSL) and the trailer jumper harness. The voltage from the STOP 15 A fuse is to the stop lamps, throttle actuator control (TAC) module, and the cruise control.
Backup Lamps
The backup lamp request signal is sent from the powertrain control module (PCM) to the body control module (BCM) on the Class 2 message system. This signal is based on the park neutral position (PNP) switch signal. The BCM supplies voltage on the backup lamp supply voltage circuit to the backup lamps and to the automatic day/night mirror. Voltage for the courtesy lamp supply voltage circuit and backup lamp supply voltage circuit is from the TBC B fuse in the instrument panel fuse block directly through the BCM to these circuits. A short to ground on either of these circuits will open the fuse. The backup lamps are grounded at G401.
For trailer wiring, a separate backup lamp circuit is connected through the underhood fuse block from the TRLR B/U 10 A fuse to the trailer wiring harness.
Turn Signal/Hazard Lamps
The IGN E 10 A fuse in the underhood fuse block supplies battery positive voltage to the turn signal/hazard switch assembly. The FLASH 25 A fuse in the I/P fuse block supplies battery positive voltage to the turn signal/flasher module and ground is supplied at G200. When the turn signal switch is placed in either the left or right position, a voltage signal is completed from the turn signal switch to the turn sign/flasher module. When the hazard flasher switch is activated, a ground signal is completed from the turn signal/hazard switch to the turn sign/flasher module. The turn sign/flasher module then sends an on-off voltage signal through the LT TRLR, RT TRLR, LT TURN or RT TURN 10 A fuses in the I/P fuse block to the appropriate turn signal or to all 4 fuses for hazard operation. The instrument panel cluster (IPC) indicators receive voltage from the LT TURN and RT TURN fuses as well as the DDM/PDM for the mirror turn signals. The DDM/PDM has no function or control of the mirror turn signals other that a pass through connection for the circuits. The audio chime is also activated when the turn signals are on. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G100. The rear turn signals are grounded at G401. The Mirror turn signals are grounded by the DDM/PDM.

Do you know how to do automotive electrical circuit testing with a test light or volt meter ? How to read an use a wiring diagram to pin point testing points . ( connectors , fuse locations etc... ) How to use a power flow chart ? Here is a site for just such info .

http://www.bbbind.com/free_tsb.html Enter vehicle info . year , make , model an engine size . System click lighting , subsystem exterior lighting . Second diagram shows trailer wiring .
Electric Testing Techniques You Need to Know

Mastering Voltage Drop Testing with Pete Meier and Jerry Truglia

CHEVROLET 2007 SILVERADO TRAILER LIGHT TROUBLESHOOTING
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