Third brake light 2018 ram pickup

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SteveSerrano

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2018
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The "third brake light no work" I see has come up many times, here's mine: 2018 dodge, was a chassis truck 5500 and came w the 3rd light just covered, ie never had had one. The truck was turned into a camper and somehow never got cited on inspection , I took off camper for latest inspection and boing! Didn't pass cause there's no 3rd brake light.... I pulled off the cover, there is a clean dry wiring harness in place, I plugged in an LED aftermarket light and the bed light illuminator white light works, but no brake light. Engine is running during checks, I've dragged wife out there over 5 times to push pedals while I check everything, again, again, and again. I cannot find a specific fuse labeled CHMSL (center high mount stop lamp) as has been the cure in other year models posted, any ideas?
 

ScubaSteve178

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I'm going to say that the lamp probably needs to be activated in the BCM.

Being as its a CANBUS system, its not just a matter of having hard wiring and switches, it all goes through the computer. I would imagine that all the power and wiring necessary is there and you just need to 1) take it by the dealer or, 2) use a tool like AlfaOBD in order to go through and activate that option.

EDIT:

This is indeed the case based on this finding from ramtrucks.com:

Cargo and Center High Mounted Stop Lamp (CHMSL) is an option on all Ram Chassis Cab vehicles. Standard equipment for the chassis cab is sales code LP8. (Delete Cargo Lamp) The option for the chassis cab is sales code LPE. (Cargo and CHMSL Lamp)
On vehicles built with no cargo or CHMSL, (LP8) the electrical connector was not removed from the harness, so it will be behind the block off cover. However, the CHMSL output is turned off in the Central Body Controller. (CBC)
If a cargo and CHMSL is installed, the CHMSL outputs can be re-enabled at a Ram dealer. Please note that this procedure is not covered under warranty. Dealer charges may apply.
To enable the cargo and CHMSL outputs, the dealer will add sales code LPE to the vehicle’s VIN as a dealer installed option in the VEHICLE OPTION UPDATES menu under the SERVICE tab of DEALERCONNECT. Once the sales code is added, the vehicle can be reconfigured using the RESTORE VEHICLE CONFIGURATION routine in WITECH. This routine can be found under the DIAGNOSTIC PROCEDURES or the MISC FUNCTIONS tab. After the vehicle has been reconfigured, a hard reset of the BCM should be performed and all fault codes that may have been set during the process should be cleared. The CHMSL will now function when the service brake is pressed.
On vehicles built with no CHMSL, (LP8) the vehicle will have been built with a head lamp switch that does not have a cargo lamp button. When a cargo and CHMSL lamp is installed, the cargo lamp will not function because the switch is not there. If it is desired to enable the cargo lamp, the appropriate switch must be ordered from the dealer and installed. There are 4 different switches to choose from. One is without cargo and fog lamps, two is with cargo and without fog, three is without cargo and with fog, and four is with cargo and fog lamps. You will need to work with the dealer’s parts department to insure the appropriate switch is ordered for your vehicle. Once the appropriate switch is installed, the cargo lamps will now function when the cargo lamp switch is pressed.
 

GsRAM

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Excellent info scuba, thanks.
 

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