2015 Kenworth T800 fog light question

It's all programmed into the ECM. All the exterior lights run through the ECM via the chassis node. Without cutting into wires and bypassing the chassis node completely (which is going to throw a lighting fault on your dash), you have to get pretty deep into the programming. If you have the Cummins, it's Insite.. if you have the PACCAR MX, it'll be Davie 4, and that's typically done through downloaded software updates. Older versions of Davie won't be compatible, and if there is a way to do it manually on Davie 4, I haven't learned it yet.. I'm still learning that program.

 

The best way you can turn the fog lights on without turning the head lights on, is to run new wires to them from an empty slot in your fuse box and use a new switch and an appropriate relay like you do on extra lights.
P.S. make sure you don't turn the factory fog light switch on because you'll get a light fault indicator on you dash. As long as you don't turn on the fog lights from the factory switch the ECM doesn't know that the lights are no longer connected to the factory circuit.

 

Depends on how well they know Insite. That stuff's pretty deep in the programming. The other way suggested will also work... however, if you're going to go that route, you'd probably be better off to unplug and cap the weatherpack connectors from the OE harness and make your own harness for the fog lights with its own connectors... that way, you don't cut into the OE harness and void the warranty.

 

Hey, that's what we're here for. But again, if you do end up having to bypass to the fog lights, I'm again going to recommend you don't cut into the OE harness... that's not just a light harness.. the way everything's multiplexed, taking out that harness encompasses taking out a group of harnesses bundled together, including all the connections to the chassis node.. if something goes tits up while the vehicle is still under warranty and that harness needs to be replaced (and it does happen), rest assured, they WILL look for a reason to void that warranty and will jump on any excuse, even if it's actually irrelevant to the reason why it's being replaced.

 

you need the ESA program, not Insite etc. with ESA you can change several lighting parameters, and while they are connected have them turn off the starter over crank protection as this has caused lots of no start issues that we have seen. Any Paccar dealer has this program.