When the alternator dies in your GMC Yukon, you better hope it's near or at your home. Once the alternator drains the charge of the battery, every electrical option in the vehicle will shut down, which will render the Yukon immobile. Maybe you have a tow service or maybe you do not. With a wrench, a ratchet and socket, you can replace this part yourself. So instead of having the Yukon towed to a repair station, have it towed home and install it yourself.
Remove the negative battery terminal from the battery using an 8 mm wrench or ratchet and an 8 mm socket.
Look for the belt routing diagram on the underside of the hood near the engine displacement sticker, or on the front frame rail. Locate the position of the belt tensioner and apply the correct box end wrench (or use the ratchet if it's a 3/8-inch-drive insert on the tensioner) to move the tensioner clockwise and relieve the tension on the belt. Slide the belt off of the alternator pulley and support it with a bungee cord or mechanic's wire to something nearby and out of the way of the alternator. This way you won't have to remove the belt and reroute the entire belt when it comes time to reinstall it.
Remove the two bottom alternator mounting bolts with a ratchet and socket.
Pry the alternator away from the carriage with a pry bar. Only pry it loose enough to position it to remove the plug and B+ wire and ground wire.
Remove the nut from the B+ wire and remove the wire and ground wire beneath it.
Unplug the field wire outlet from the alternator.
Reverse the procedure to replace everything. Be sure when replacing the belt back onto the alternator that you do not force it on. You may need to apply a little force, but you should not have to overly force the belt on. If it does not seem to want to fit on, you'll have to inspect the routing of the belt to see if it slipped off a pulley somewhere.
