Hello all, newbie here.

Bit of an obscure issue: I put a new aux belt on a 2009 ford focus, 2.0 duratec he engine. The new belt screams on high alternator usage (headlights and screen defroster turned on for example). Car has no sign of battery or alternator issues. The manuals I can find suggest the belt should have an automatic tensioner, but instead the car has this which seems to only be a pulley and has no adjustment, manual nor autonatic.

the existing pulley I believe is this https://www.ebay.co.uk/itm/Genuine-Ford-C-Max-Focus-MK2-Drive-Belt-Tensioner-Pulley-Kit-1465253/272376270305 and the auto adjusting one that shows up when I search for a replacement is this https://www.ebay.co.uk/itm/FORD-FOCUS-Mk2-2-0-Aux-Belt-Tensioner-04-to-12-Drive-V-Ribbed-INA-1251661-New/332450482629 which I don't think can fit as the mount holes aren't in the same place and are much deeper. I'm considering trying to find a larger pulley wheel but I'd like to know if I'm doing something wrong?

thanks in advance for any help!

You sure you got the right sized belt? And if so, how did you manage to fit belt. The belts and tensioner changed around 2008/2009

belt is the same size and part number as the old belt (though this was squeaking too), I think 1250mm. I cut the ac stretch fit off, pivoted the top pulley and removed the old belt,routed the new belt and pulled back on with the pulley, I didn't see anywhere to tension the belt, but I could have missed it

There is no tensioner as such, relies on the tension after pivoting the top pulley back in place. How long had the old belt been screeching for? 

Since the colder weather really so a little over a month, haven't had a winter with this car yet

Was the new belt marked as a stretch type belt? I used a Gates branded stretch belt on my Focus 1.8 Petrol and it worked fine.