Need help hooking up are topper brake light

jim larson · June 15, 2020

Got tired of the fold-a-cover and when back to a topper cap on my 2017 silverado crew caab. Bought used, I have lights in my box, so just need to hook up the brake light in the topper. So I don't want to use a 4 pronged harness. Unless there is a close spot where I can get power for the topper light switch. Is there any such animal as I don't want to take t he time to run a wire to the battery for that.

So what the best way to hook up the brake light? Just cut the plug off from the part of the harness in the topper? Then how do I connect the two wire to something back where the wires are for the rear tail lights?

Ravenkeeper · July 17, 2020

On 6/15/2020 at 10:42 AM, jim larson said:

Got tired of the fold-a-cover and when back to a topper cap on my 2017 silverado crew caab. Bought used, I have lights in my box, so just need to hook up the brake light in the topper. So I don't want to use a 4 pronged harness. Unless there is a close spot where I can get power for the topper light switch. Is there any such animal as I don't want to take t he time to run a wire to the battery for that.

So what the best way to hook up the brake light? Just cut the plug off from the part of the harness in the topper? Then how do I connect the two wire to something back where the wires are for the rear tail lights?

There is at least one j-box under the bed that you could tap into. I know some of the guys have tapped into that for their bed lights. When my dad did the shell on his 72 Datsun PU, he used a trailer 4-wire harness, with the connector near the shell where the wires were hanging, but this was for the clearance lights, interior cargo light, and exterior hatch light. Even when he bought my 91 Nissan King Cab, he did the same thing, or had the place that he bought the shell from connect it. Neither one had third brake light, I don't think.

GrayGhost_ · July 17, 2020

TSB on this

https://static.nhtsa.gov/odi/tsbs/2017/MC-10126990-9999.pdf

Bulletin No.: PIT5314BPublished date: 12/21/2017Preliminary InstructionsFollow the recommendations listed below based on the model year of the vehicle.2016-2018 model years

Perform the following recommendations based on vehicle configuration:

1. For vehicles built WITH Under Rail Bed Lighting Option:Trucks equipped with the under rail bed lighting option will already have the female side of the X400 connector. Obtain an appropriatelength of 18 ga wire to run from the X400 connector up to the CHMSL wiring for the cap or topper. Use terminal part # 60012931 in AFLTray 21, along with wire seal part # 60994015 in AFL Tray 21 and connect it to one end of the wire. Disconnect the X400 connectorand remove the rubber cavity plug in pin position 4 and discard. Install the terminated lead that was just made into the X400connector pin 4. Run the wire up to the CHMSL for the cap or topper and connect. The ground for the cap or topper CHMSL willneed to be made to an appropriate ground.

2. For vehicles built WITHOUT Under Rail Bed Lighting Option:Trucks not equipped with the under rail bed lighting option will have a dummy X400 female connector, which will be removed anddiscarded. The female side of the X400 connector is not available separately, but can be obtained by ordering the under rail bedlighting harness GM part number 23327843. The harness will come with terminals/wiring in pin positions 1 and 6. Remove the wiringand terminal from pin location 1 and discard. Move the rubber cavity plug from pin position 4 and reinstall it into pin position 1. Obtain an appropriate length of 18 ga wire to run from the X400 up to the CHMSL wiring for the cap or topper. Use terminal part #60012931 in AFL Tray 21, along with wire seal part # 60994015 in AFL Tray 21 and connect it to one end of the wire. Install theterminated lead that was just made into the X400 connector pin location 4. Pin 6 is a ground circuit that is used for the under rail bedlighting and it can also be used to ground the CHMSL for the cap or topper if the wire gauge size in the connector is of the proper sizefor the CHMSL in the cap or topper. If the wire gauge size is too small, any of the following can be done:- Make a second wire as described above. Then, remove the wiring from pin 6 and discard. Install the new terminated wire in position6 for the ground and run it up to the CHMSL for the cap or topper and connect.- Remove the wire and terminal from pin 6 and install a rubber cavity plug.- Cut the wire for terminal 6, leaving a couple inches of wire, and seal the end of the wire.NOTE: The terminal removal tool for the female side of the X400 connector is J-38125-212.