That truck should already have dual alternators on it. I have six F-450 2WD service trucks in my fleet (a MAJOR West Coast Fire department) & all of them have dual alts standard- in fact, Ford built them no other way. The top alternator is about 140 amps & the bottom unit (right/lower in front of the exhaust manifold) is 120 amps. If for some reason you have a single alternator set-up (one large one centered on top), then you can get the complete dual set-up with wiring from a wrecked/salvaged E350 or E450 Ford Rescue Ambulance package. Get the whole enchilada: serpentine belt pullies, idlers, A/C pulley, W/P pulley, tensioner, etc. The dual alternator package may have a wider belt on the E Series than the F Series & belt width is critical. There's a difference in the wiring harness, too. Good luck.
For a 2001 Ford Escort ZX2 ( in North America ) ( No ) it has the 2.0 liter Dual Over Head Cam Zetec four cylinder engine
There is an easy way to tell if your Ford Focus is a single or dual cam shaft. If it is single, it will have one gear with a belt around it.
dual
According to my Consumer Guide book : SOHC and DOHC depending on model
DOHC
it is a dohc engine.
In a 2001 Ford Escort ZX2 ( for North America ) That is a 2.0 liter Dual Over Head Cam four cylinder engine
In a 2001 Ford Taurus : ---------------------------------------------------------------------------------------------------- The 3.0 " Vulcan " V6 engine , and its flex fuel version is an ( Over Head Valve / pushrod design engine ) ----------------------------------------------------------------------------------------------------- The 3.0 " Duratec " V6 engine is a ( Dual Over Head Cam design engine )
According to my Chilton's Auto Repair Manual : The 351 Cleveland engine has single points and the 351 CJ engine has dual points in 1973
In a 2001 Ford Focus : The 2.0 litre SPI engine ( Split Port Induction ) is a Single Over Head Cam four cylinder engine ( the other available engine was the Dual Over Head Cam Zetec-E engine in certain models )
With single alternator , 110 amp -------------------------------------------------------------------------------- With dual alternators : lower , 120 amp , heavy duty upper , 140 amp , heavy duty
it is not watts, but amps. If you are just adding a stero you should be fine. But, if you are adding several amps and equipment, check into a higer amp alternator (good luck on a Focus) and dual batteries with an isolator. If you run dual batteries without the isolator it will not work as well.