I dont know if anyone has tried to install a line lock on a 1991 mustang or not, but I have been tech'n with the manufacturer for the last week. The only way I have figured out a way to get this to work is by two ways: (1) get a 1986 Master Cylinder, 1986 distribution block, and a 1986 main brake line. If you go this route you will have to put the solenoid between the master cylinder and the block with it "T'ing" out of the block to the left and right. And (2) buy a second solenoid. The way my brake system is set up is two lines coming out the side of the master cylinder going to the block. One coming out of the block to the front right caliper, the other to the rear. Then there is another line coming out of the bottom of the master cylinder that goes straight to the front left caliper. I have never seen anything like this before. You will have to come out of the master cylinder (the bottom line) and tap the solenoid into there. No big deal, just finding the right fitting to take a double flare to a single flair. Then you can tap the other solenoid into the front right after it comes out of the block. All that is left is tying the electronics together and running the button. If anyone else has a better solution, please reply. I talked to several manufacturers. Moroso, Hurst, Biondo Racing, and two of the three told me to call the other ones. If not, I hope this helps the next install.