1. Check the Backup Light Switch:
* Location: The backup light switch is typically located on the transmission or transfer case. It's a mechanical switch that activates when the transmission is in reverse.
* Inspection: Visually inspect the switch for any damage, corrosion, or loose connections. Wiggle the switch gently while someone checks if the backup lights react. A faulty switch is a common culprit. If you find corrosion, clean the connections carefully. If it's physically damaged, replacement is necessary.
2. Investigate the Wiring Harness:
* Wiring Diagram: Obtain a wiring diagram for your specific 1987 Jeep Wrangler model. This is crucial for tracing the wires correctly. You can often find these online through Jeep forums or repair manuals.
* Continuity Test: Using a multimeter, check the continuity of the wires between the backup light switch and the lights themselves. You should have continuity *only* when the transmission is in reverse. If you have continuity when the transmission is in neutral or park, you've located a short.
* Ground Connection: Check the ground connection for the backup lights. A poor ground can cause all sorts of electrical gremlins. Clean any corrosion from the ground point and ensure a solid connection.
* Look for Damaged Wires: Carefully examine the wiring harness for any frayed, melted, or broken wires, especially near the transmission and where the harness might rub against other components. Repair or replace any damaged sections.
3. Relay and Fuse Check (Less Likely, But Possible):
* Although less common for this specific problem, a faulty relay or a blown fuse could theoretically contribute. Check the fuse box for any blown fuses related to the backup lights or the headlight circuit. Also, inspect any relays associated with these circuits. If you have a spare relay, you can test it by swapping it in.
4. Headlight Switch (Less Likely):
* While less probable, a faulty headlight switch *could* be causing a cross-circuit. If you've eliminated all other possibilities, you might consider investigating the switch.
Troubleshooting Steps:
1. Start with the easiest: Begin by inspecting the backup light switch. This is often the source of the problem.
2. Isolate the short: Use the multimeter to trace the faulty circuit. This will pinpoint the location of the short circuit.
3. Repair or replace: Once you've identified the faulty component (switch, wire, etc.), repair it or replace it with a new part.
Important Safety Notes:
* Disconnect the battery negative terminal before working on any electrical components to prevent shocks or short circuits.
* Use caution when working near moving parts, such as the transmission.
* If you are uncomfortable working with automotive electrical systems, it's best to take your Jeep to a qualified mechanic.
By systematically checking these areas, you should be able to pinpoint the cause of the problem and repair your Jeep Wrangler's faulty backup light circuit. Remember to always consult a wiring diagram for your specific model year to ensure accurate identification of wires and components.
