Trying to replace the serpenting belt on my ford 150. I cannot get the new belt on, even pushing the tensioner as far as I can. Just a little short. I feel like I could do it if I had three arms, but alas.... Should I remove the idler ?? I've double checked and the new belt is the correct one. Putting the old belt back on was a snap. Suggestions please.......

 

You can try stretching the new one a little by hooking it around a fence post and tugging of it a bit . That may stretch it enough to go on.
Jimmy

 

Usually it is easiest to install the belt around a smooth pulley last, such as the idler. If you hold the old belt and the new belt together are they the same length?
New ones quite often are a pain to install but shouldnt be that bad.