BestKeys 1999 Mercury Grand Marquis Replacement Transponder Ignition Chip Car Key 4C 1999 Mercury Grand Marquis Replacement Transponder Ignition Chip Car Key 4C w/ Free DIY Programming Programming this key requires 2 working unique (not cloned) keys. If you do not have 2 working unique (not cloned) keys you will need to have the key programmed at an automotive locksmith or dealership. We will provide a link to our website with Free Do-It-Yourself programming instructions with your order. Dealer or locksmith program if you only have 1 existing key YOUR KEY SUPPLIER is the only authorized seller of BESTKEYS products. All warranties will be voided if bought from any other sellers.