He's getting some response to it. That would rule out the brake light. Brake light gives the whole amp a key ground. If it were the brake light he'd be getting nothing. Because he is getting surging and weirdness, it points to first the amp, then the stalk. Probably not the actuator unless its pulling just enough over amperage to weaken the solders in the amp.

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg