I've searched this and couldn't find anything.
My ABS and brake light come on any time it's 60f or below. Wet or dry doesn't matter and if I shut down and start back up after doing a couple of miles to warm up they stay off.
I had replaced the sensor after the speedo quit and both lights came on. I used a MOPAR part bought from a dealer (wow filter doesn't like bad mouthing dealerships?). I traced all the wires and used electronics contact cleaner/prep on all the plugs.
I hate to buy another part on the possibility that it's defective only to keep getting the same symptoms.
Does anyone know what this could be?

 

Check your vacuum lines, you might have a leak. Both my brake and ABS lights were on when I had a leak in my last truck. Sometimes you can even hear it for a few seconds after you shut her down. If not wait a minute and then disconnect one of them, it should whosh.

 

With amber light on, a good possibility there is a fault code, that could be read with a code reader.
Let's see, lights on when temp drops below 60 degrees. Goes off after driving for few minutes or warm up. HUmmmmm!!! Have you released caps on MC? Sounds like vacuum builds as fluid cools. Maybe the MC is not functioning correctlly when cold!!!! OH! yes. Adjust rear brakes of course.

 

I don't think this will help but some more info for you, I have a 99 that had a busted spider gear in the rear which wiped out the end of the speed sensor. Then the tone ring on the ring gear was damaged, anyway when ever the speed o hits 75mph it triggers the ABS and Brake lights till the truck is shut down and restarted. not the same problem but the same result. Good Luck

 

Thanks for the responses.
I checked out all the lines under the hood and no leaks. I pulled the sensor and put a stick magnet into the pumpkin (I risked having to pull it apart instead of actuall pulling it apart) and there were no iron chunks so the gears are prolly fine. I tried the scanners available at two different parts places and they don't read any codes.
That leaves going to the brutally honest, never take advantage, never over charging dealership and let them read the codes or trying a new sensor.
I guess the sensor wins because I can buy 3 of them for the cost of a single diagnostic

 

Actually you can test the sensor yourself.
1. Does speedo and odometer work correctlly at all temps?
yes equals circuit and sensor intact.
No equals futher testing required or wiring and sensor.
If futher inspection required. You can pull axle speed sensor out and with mirror inspect the tone wheel.
Parts store readers generally only read engine codes is not mistaken.