Been reading lots of posts here on aux sw and pass through wiring and finally decided to tackle locating these wires in my 2108 SCrew, exposing them sufficiently to make connections, and testing the operation of the aux switches before proceeding with the install of several BD light kits. In going through this drill, I found some conflicts with info posted on this forum in another thread by others (more below).
1. The wire bundles for the aux switches and pass through wires were well hidden. It took some poking around with a flashlight to find them. Each bundle was taped to a nearby wire harness in two places with electrical tape. Getting at the electrical tape to free up the wires was a bit of a challenge, as this was under/behind various structures and other wiring/connectors. No room to get fingers in there to remove the tape so I used an Xacto knife to cut the tape, after which it was easy to pull out the two wire bundles and verify that the colors match what others have published for wire colors for 2108 trucks (different from 2017 trucks, and different from the owners manual supplement for 2018 trucks).
2. Next task was to identify which wire bundle was which. There are posts on this site with photos marked to show that the wire bundle nearest the passenger side contains the aux sw wires. This turned out to be the wrong info for my truck. I put a Posi-Tap connector on the Aux 1 switch wire (green/white) in each bundle, connected the tap to a voltmeter, and operated the Aux 1 sw. No indication on the bundle closest to the passenger side when the sw was operated. On the bundle closest to the driver side, 12 volts indicated with the Aux 1 sw in the on position. So, on my truck at least, the bundle closest to the driver side contains the aux sw wires, and the bundle closest to the passenger side contains the pass through wires. YMMV. Both bundles had wires of adequate length to make connections, but not what I would call a generous length. Wire sizes looked on the small side, but probably OK for the rated current.
3. I also did some tests to determine how to power the BD reverse light kit. Several here have suggested not tapping into the drivers side OEM backup light wiring (as recommended in the BD installation instructions) due to the small wire size, so I started looking for other possibilities. There is easy access to the back side of the 7 pin round trailer connector on the rear bumper; the center pin on this connector provides power to trailer backup lights. I put the truck into reverse (with the engine running) and measured the voltage on this pin; 12 volts in reverse, 0 volts in park. With the easy access to the rear of this connector, I will attach a Posi-Tap connector to the wire going to the center pin and use the tap to power the reverse light kit. No wire cutting or splicing necessary and easily removable.
With this preliminary prep work done, the rest looks easy enough.
1. The wire bundles for the aux switches and pass through wires were well hidden. It took some poking around with a flashlight to find them. Each bundle was taped to a nearby wire harness in two places with electrical tape. Getting at the electrical tape to free up the wires was a bit of a challenge, as this was under/behind various structures and other wiring/connectors. No room to get fingers in there to remove the tape so I used an Xacto knife to cut the tape, after which it was easy to pull out the two wire bundles and verify that the colors match what others have published for wire colors for 2108 trucks (different from 2017 trucks, and different from the owners manual supplement for 2018 trucks).
2. Next task was to identify which wire bundle was which. There are posts on this site with photos marked to show that the wire bundle nearest the passenger side contains the aux sw wires. This turned out to be the wrong info for my truck. I put a Posi-Tap connector on the Aux 1 switch wire (green/white) in each bundle, connected the tap to a voltmeter, and operated the Aux 1 sw. No indication on the bundle closest to the passenger side when the sw was operated. On the bundle closest to the driver side, 12 volts indicated with the Aux 1 sw in the on position. So, on my truck at least, the bundle closest to the driver side contains the aux sw wires, and the bundle closest to the passenger side contains the pass through wires. YMMV. Both bundles had wires of adequate length to make connections, but not what I would call a generous length. Wire sizes looked on the small side, but probably OK for the rated current.
3. I also did some tests to determine how to power the BD reverse light kit. Several here have suggested not tapping into the drivers side OEM backup light wiring (as recommended in the BD installation instructions) due to the small wire size, so I started looking for other possibilities. There is easy access to the back side of the 7 pin round trailer connector on the rear bumper; the center pin on this connector provides power to trailer backup lights. I put the truck into reverse (with the engine running) and measured the voltage on this pin; 12 volts in reverse, 0 volts in park. With the easy access to the rear of this connector, I will attach a Posi-Tap connector to the wire going to the center pin and use the tap to power the reverse light kit. No wire cutting or splicing necessary and easily removable.
With this preliminary prep work done, the rest looks easy enough.
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