His effect's setup has also been an integral part of his sound. During his classic period, he used a hydrid pedal board consisting of a Univibe, two Electric Mistress boosters, a Mutron flanger and a couple of homemade boxes. The board itself was rigged by his guitar tech and included a pre-amp that boosted the signal and prevented noise. But, for a period starting in the late 80's, he reverted to a more basic setup simply consisting of a Jennings Cry Baby wah wah, a Tube Works booster and a plain vanilla Boss chorus pedal.
By the way, Trower is notorious for not revealing the exact settings of his effects and amps. His opinion is because most of his gear throughout the years has been modified - the settings are irrelevant. Still, even when he has used stock equipment, he hasn't let interviewers know how he sets up his rig.
Guitars
The one consistency throughout the years (dating at least from 1971's Broken Barricades) has been his Fender Stratocasters. In the late 70's and early 80's, he used two 1966 Strats (both stock), one with the E-string tuned down to a D. He outfitted a third Strat with Bill Lawrence humbucking pickups to cut down on noise at difficult gigs.
Later on, in the 90's, he changed to custom Strats, made by Fender to his specs. In particular, he seemed to alternate between one with stock pickups and another outfitted with Lace Sensors. His decision to switch to new guitars (as opposed to his earlier use of 50's and 60's models) came about because he had 15 vintage guitars stolen in 1979, and ultimately felt that he didn't want to become dependent on one or two irreplaceable instruments.
Trower's main tip for setting up a Strat is to keep the action high. He tests them by first playing without amplification--then, if the guitar sounds true, he'll plug it in. As far as strings go, in the 70's and 80's, he used a fairly top heavy Ernie Ball set (.011, .015, .016, .024, .034, .046). Remember though, he was tuning down a half step during this period (see section on tunings below). Later, for In The Line Of Fire in 1990, he used an extremely top heavy set of .012, .015, .017, .026, .036 and .046! To the best of my knowledge, he was tuning to A440 for that album, so I'm at a loss to explain how he could bend the strings with any efficiency.
For the record, he claims to use a three-position toggle switch (instead of the modern five way variety) and favors the middle position for rhythm. The song, Bridge Of Sighs, was played in the middle position, but for Daydream, he used the back pickup. For most of his career, Trower also disabled the "whammy bar" by placing a wood shim between the springs and the body. With the newer Fenders, he relies on their locking machine heads and now uses the whammy at times.
Amps