I have an answer to this old question.
BTW, the price of the LEDs will not matter.
For the cruise control to work, you will have to add a load resistor across the ground wire(w/ black stripe) and the brake wire and then another resistor across the ground wire and the tail light wire.
The LEDs are consumming too little current. The cruise controller thinks you are constantly applying your brakes. Adding the 6 ohm load resistors will create another 2mA path for the current to flow.
If you want LEDs on your turn signals, you will have to do the same thing.
Check Ebay for the
load resistors