accessory belt still very loose after replacing alternator

[andrewwynn]

Step one is to compare old and new belt. You can measure with a string so you don't have to remove the new one. Make sure they are the same length. Then as suggested above your check the path. It took me a good 20 minutes to figure out the path on the M62 it's a doozy. There are a couple incorrect possibilities that will run all the parts but won't use enough length.

Basically most pulleys will have more than 180° wrap. If that's not the case you probably made a wrong turn