I have an ABA set of F3's and they are all powered. No MU wire. I can run any of them, even the B unit, by itself. I cannot remember the maker. Might be Weaver or Atlas. They are 2 rail.
Rick
Hi guys, it's me again. I just checked on that F3 ABA set and guess what????? It IS MTH 2 rail scale. NO tether between the units. Kadee couplers. And like I said before all units are powered and can be run individually.
Hold on there Rick. All MTH F units (FT, F3, F7) built with ProtoSound 2 or 3 have powered As with the trailing A unit slaved to the leading A unit. The A units are connected by a tether. B units are unpowered and have tethers to pass trough the signals and lighting between the A units.
The earliest MTH F3 sets made in the 1990s were conventionally controlled, available in 2 or 3 rail and had only the lead A unit powered. If more power was desired powered B units were available as were dummy Bs.
Either you have a conglomeration of 1990s vintage MTH F3s with all powered units, more modern MTH F units where someone has added power to all of them and removed the slave board and tether of you don't have MTH F units.
If you have the box with the product number or photographs I think we can identify what you really have.
In answer to Mark's original question, if you are looking for O scale MTH F units made in this century only the A units are powered and they can not be run as two separately controlled independent units.
In HO MTH Proto 3 Fs and PAs are untethered independent locomotives that can be consisted together.
Hope that helps. 
