Just picked up my first Ford, a 2010 FX4 F150 crew cab last week. Lots of aftermarket goodies, still tons I want to do with it, and my boyfriend is happily feeding my desire to upgrade (he's got a 2011 FX4 F250). I'm in love! Except the blinker issue. They all work. Both left and right blink at a normal rate, until I hit the brakes. They'll start blinking really fast like a bulb is out, but they're all still working. Both front and rear are aftermarket set ups, but I don't see how that could be causing this issue..? Anyways, input and a direction to start looking would be greatly appreciated, as this is driving me nuts.

Pretty excited to have this truck and get my plans going for this thing!
Thanks guys!

 

I hope this helps. Looking at the pic of the front of your truck. You have LED's turn signal lights. You need to add a resistor to it. Because since the LED draw little current. The truck thinks a bulb is burn out. If you do a search on here. You'll find more detail information on this.

 

Might pull the tail light bulbs and look at them just to be safe. They are dual filament bulbs and if only 1 filament is broken they will appear to work and make a fast blinker with the brake light on as well. I bought a used Escort a while ago and it had a bulb on each side with 1 filament out and it did what you are describing.

 

I had a similar issue with my 1999 Dodge Ram 1500, the problem ended up being a bad ground in the rear of the vehicle. Check your grounds!

 

Your bulbs are dual filament. If one of the filaments is burned out it will blink fast when you apply the brakes as you describe but it is hard to notice visually so it appears the bulb is normal.
Oops Sorry Chrisc321, didn't see your post...the thunder is yours!!

 

If my attachment decides to work, these are the tail lights. I'm going to check for resistors and grounds this evening after work, however my front blinkers aren't LEDs. They're amber, only LED's are the headlights and 3rd brake light (which the passenger side is out on).

 

It looks like your heads and tails are spyder brand which from what i hear are really cheep and poorly made if anything its you brake lights cause if its a spyder then those are leds they are just built in and have resistors built into them and if the resistor in them went out or has a bad connection then it could cause the hyper flash if it were me id ditch the head and tail lights on there and just get the Black halogen OEM housings you can get both OEM heads and tails for about $360 on eBay or if you really want you can get a pair of OEM HIDs from theretrofitsource.com they sell the whole kit for $1250 for black