I have two WH8 ballasts and run 2x54w lamps with each one. For some reason the specs for the WH7 say you can run 3 or 4x54w but not two. When running 3, one of the red wires is capped off, wiring diagram #8. It would seem logical that you should be able to run two lamps by simply capping off two red wires, but maybe Fulham knows something we don't. I would be inclined to take Fulham's word in this case, after all, they manufacture the ballast, not Custom Aquatic.
In addition to the wiring diagrams, there is also a lamp chart available showing the various lamp/ballast combinations. This also corroborates the 3 or 4 but not 2 x 54watt lamps for the Workhorse 7. See following link:
Fulham Lamp Chart
Some info I had saved to a text file, can't remember the source, but also agrees with the lamp chart... text in parentheses are my own ramblings/theories. Both ballasts have the same maximum wattage, the WH8 has 6 red wires, the WH7 has 4.
Workhorse 8, Long Case, 120 volt Solid-State Electronic, Case Size, Height - 1.0", width -
1.72", Length - 19.25", Max. Power 220 watt, Max. Current 1.8 Amp. Instant start, Operating
Temperature -20° F (-30º C) to 158º F (70º C) Low Cost Freezer Ballast Replacement. Sound
Rated A. Do not use for remote mounting.
Workhorse 8 will operate following T5 Lamps
F24T5 HO - 4, 5, or 6 lamps (24 watts each - overdriven @36.66)
F39T5 HO - 3 lamps (39 watts each - overdriven @73?)
F54T5 HO - 1, 2, or 3 lamps (54 watts each - over or underdriven?)
F80T5 HO - 1 lamp (? watts each ?)
Ballast has 6 red wires, thus 220 watt/6 = 36.66 watts per wire
Workhorse 7, Long Case, 120 volt Solid-State Electronic, Case Size, Height - 1.0", width -
1.72", Length - 18.5", Max. Power 220 watt, Max. Current 1.82 Amp. Instant start, Operating
Temperature -20° F (-30º C) to 158º F (70º C) Low Cost Freezer Ballast Replacement. Sound
Rated. A Do not use for remote mounting.
Workhorse 7 will operate following T5 lamps
F39T5 HO - 4 Lamps
F54T5 HO - 3 or 4 Lamps
F80T5 HO - 2 Lamps