My son lost his only key for his 99 Ford Ranger.
I purchased a replacement column, which included one chip key. I swapped the columns, and now can't get the truck to even turn over. It's flashing the 15 code, and I'm not sure how to reprogram this key to communicate with the truck.

 

Call a mobile locksmith. There's no quick-n-easy DIY method. If there was, PATS would be worthless.

 

While you have the mobile locksmith there, they will have to make second ignition key, he will have to have 2 keys to program it.

Don't forget to have them make you 2 door keys for the truck so you don't lock yourself out.

 

Personally, I always get 4 chipped keys. I put two on 'em in my safe and I know I'll never have to make another key as long as the truck is roadworthy.

 

Just an FYI for anyone that runs into this in the future:
In 98-02 The Ranger used PATS system B, which requires three separate & synced components plus the transponder key in order for the truck to run.
They are located in three different places and swapping the column only replaces 1 of them. If you don't want to go the locksmith route you will need to get all three of these from the same truck:
1) the PATS-specific module and bracket located within the steering column, which are removable without taking the whole column
2) the truck's ECU, and
3) the PATS module located under the dash behind the passenger airbag.

am