The trick to reinstalling the alt easily onto the bracket is to refit the long mounting bolt (on the bench). Spray it with penetrating oil and lightly whack the bolt head a few times with a deadblow/rubber hammer. This moves the sliding nut back a few mm and is easily refitted. The captive nut is made to slide. Don't get carried away, a few light taps are all you need.

Also, there are at least two different Valeo alts depending on the options/packages, maybe 100amp and 140 amp. If you have heated seats, you def have a 140amp.

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