Horn and lights activate by themselfs

Were you parked by a........cemetery?

 

Sounds like an issue with a SAM. Not a whole lot you can do with them without hooking it to service link. Any faults should display on the dash.

You can check your battery and starter connections. I'm not sure about 2013's, but the 2010's that we got had mega fuses under the drivers door that were prone to corrosion. Low voltage can cause weird issues on those.

 

on new trucks the horn will blow on and off if you park and don't set truck brake and turn truck off. light not sure but maybe they are hitting the auto light check button in cab.

 

It is the high voltage agm relays located above the battery,there is 4 of them.2 are 125amp the other are 2 are 175 amp. When they start to fail your lights on your truck and trailer will flash. You have to change them and always keep a spare .Once they completely fail your truck will shut down.

 

Had same problem on a 09 windshield was leaking water onto computer hopefully that's not your problem if your off warranty was $4500 fix had to do two computers and harnesses floor never got wet only clue was a occasional odd smell in cab.. The 2010 and up were supposedly fixed with a new style gasket

 

Lights: check the headlamps pigtail connection.

 

I have a Freightliner Cascadia evolution 2016 Isx , yesterday city horn and washer pump started turning on and off by it’s own, while driving and also while parked without key in. I ended up disconnecting both, does anyone know about this issue?