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Q: left rear tail light,brake and turn signalwont work when headlights are switched on on 2007 Jeep Grand Cherokee

left rear tail light, brake,and turn signal stop working when headlights are switched on. brake and signal works when not on. all bulbs are good.
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Because of the complexity of today vehicles electrical systems, it is best left to the qualified Technicians at your local dealership to inspect and diagnosis. Self diagnosis can lead to very expensive repairs. Here is a short summary of what is involved in your scenario.
The lamps and the hard wired circuits between components related to the exterior lighting system may be diagnosed using conventional diagnostic tools and procedures.However, conventional diagnostic methods will not prove conclusive in the diagnosis of the exterior lighting system or the electronic controls or communication between modules and other devices that provide some features of the exterior lighting system. The most reliable, efficient, and accurate means to diagnose the exterior lighting system or the electronic controls and communication related to exterior lighting system operation requires the use of a diagnostic scan tool. The lighting system incl;udes the following modules, Steering Control Module (SCM), Front Control Module (FCM) and the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN). These modules all work communicate together over a CAN Bus circuit.

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