The DEPRESS FULLY switch is a momentary contact switch that springs back to OFF as soon as you let go of the switch.
I can't see how you could damage the motor in the valve.
It's a DC motor that spins different directions based on the polarity of terminals D & E.
The Dual Tank Theory of operation writeup may help clear things up for you. You have the 81-91 system in post #2.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8
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