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In connection with the installation of such devices, please note the following. 1. Check the installed rear SAM. If a rear SAM with part number A164 540 78 45 or A164 540 88 45 is currently installed, a new rear SAM must be installed and version coded. The current part number is listed in the parts information section below. The cost of this update is not covered by warranty. Note: Some vehicles without a factory trailer hitch are equipped with a rear SAM that requires replacement with a different rear SAM if trailer brakes are to be retrofitted. 2. Locate plug X58/28. This contains the four wires needed for the electric trailer brake controller Refer to the below for wire description. a. Up to December 2006 production, X58/28 (Figure 1, green plug) near the rear fuse box F4 (Figure 1). Plug may be tie wrapped to harness below Rear SAM. b. As of December 2006 production, X58/28 (Figure 2, green plug) near the diagnostic connector X11/4 (Figure 2). Plug may be tie wrapped to harness above connector X11/4. Figure 1 T-B-31/1907 Figure 2 T-B-31.19/07d Wire Description – X58/28 Color Size Description Red or Red /Blue 2.5 mm2 Fuse F4f71, 30 Amp fuse. This is the power supply for an electric trailer brake controller. Brown 2.5 mm2W7 ground. This is the ground wire for an electric trailer brake controller Grey or Black/Red 0.75mm2 Brake light circuit. This is the brake signal for an electric trailer brake controller (input to the electronic brake controller). Yellow/Red or Yellow/White 2.5 mm2 X58/11 pin 7. This is the variable voltage signal to actuate the trailer brakes (from the output of the electronic brake controller). Note: Most electric trailer brake controllers specify that the power supply must be wired using a self resetting circuit breaker. Follow the instructions supplied with the electric trailer brake controller. Note: The above variation in wire colors depends on production date of factory harness and or installed accessory harness. Warning! The electric trailer brake controller must be adjusted according to the instructions supplied with the electric trailer brake controller, which requires the trailer be connected to the tow vehicle