I recently had this issue and I was able to resolve the problem by researching it online. I just had my transmission replaced on my 2008 F150 XLT SuperCrew. When is was done I had a bunch of maintenance work that needed to be done on my truck, 130000 miles and several things were addressed. Spark Plugs and Wires, Air and Fuel Filters were replaced, Fuel Injectors were flushed and cleaned, Coolant was also flushed and cleaned and new Antifreeze added. Brakes were checked and all other fluid levels checked. Well a couple days after all this work was done I started my truck and the ABS and Brake lights on the dash stayed on and didn't go off like they normally do. I didn't notice any issues with either of the braking systems. I did notice that my Cruise Control wasn't working and my Reverse lights weren't working. All these issues at once told me from experience that I had better check the fuse box. That is when I found the #14 fuse a 10 amp blown. I had a spare 10 amp in the truck so I quickly changed it and checked everything that was working before and verified all nonworking things are now working again and the lights on the dash were off. Problem solved. So I thought anyway. The next day I start my truck and the ABS, and Brake lights on the dash are back on. I checked the fuse again and sure enough it was blown again. I grabbed my phone and googled the issue and found the same issue in another forum on two different sites. After reading both sites thoroughly and investigating my truck for the same issue I found that my PCV Heater wires were shorted out at the PCV Heater. the two wires led right into the part at the valve cover and it got hot enough to melt the coating off both wires which caused them to short out the system when they made contact with each other. I didn't know I had a PCV Heater and I didn't know what it's purpose was. I learned that this part helped warm the engine in very cold climates. I also learned that the dealer wanted $70.00 for a new one. I changed the fuse again and disconnected the wires from the PCV Heater then started my truck. No lights on my dash were on and the truck seemed to be running fine. I turned the truck off and started it again about 4 more times just to be sure I had solved the fuse blowing issue. So far so good. Now I live in California and it doesn't get very cold here so hooking the PCV Heater back up wasn't going to happen and won't happen in the future unless some other issue arises from it not being connected. I am very thankful to the two other guys that had this same problem and posted it in the forums that they did. I would have had a helluva time trying to find that short if it weren't for them. I took a picture of the PCV Heater with some electrical tape on one of the wires. I'll post it with this thread. I hope it helps someone the way I was helped.

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Thanks for posting the fix

 

I don't play in the gas engine world much, but good find and thanks for posting the pic and fix

 

Fuse 14 kept blowing, 2008 F-150 XLT 4.6 finally after two years I found the cause! Wiring harness from transmission up to connection on fire wall. Harness had contacted passenger side exhaust manifold and burned and grounded circuit serving back up lights, AC high limit compressor switch, ect. Pulled the harness, made repairs. Everything is now operational! Expect the unexpected.

 

Check the wiring harness from the left side of the transmission all the way up to the firewall plug. I found my direct short there. Spent two and a half years looking for this &&@$&$! Found it! The harness had gotten too close the the passenger side exhaust manifold. boom. Good luck!