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repalce the power transister((item B) it is bad this provides the ground you have power.
How the Circuit Works The heater control panel controls the blower controls, air delivery, and A/C compressor controls automatically. With the ignition switch in ON (II), battery voltage is supplied through fuse 14. The control unit is grounded at G502.Blower Controls You can manually select the fan speed by turning the fan control dial clockwise, from the OFF position. Turning the dial further clockwise increases the fan's speed, which increases air flow.Battery voltage is applied through fuse 14 to the blower motor relay contacts at all times. With the ignition switch ON (II), the blower motor relay in the under-hood fuse/relay box is energized which feeds battery voltage to the blower motor. The blower power transistor controls the blower motor in all speeds except HIGH. The blower power transistor is controlled by the heater control panel. When the control panel requests HIGH blower speed, the blower power transistor grounds the blower motor which connects it directly to ground, making the blower run at high speed.
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i tell you what on high it still goes thru power relay that is how it gets it ground on high on medium on low and if you have power at blower all you need is ground tha tis what is wrong. did you backprobe to ground this would have verified this. check ground number g502
make sure you check fuse f14 and fuse 12
g502 under right side of dash
here is how it works if you have 12 volts at blower and you have a ground to battery that blower should work.
you say you have power hook a ground up to battery negative and back probe the connection it has to work.
hook the test light to the connection coming to blower blue and white should light up.now keep it connected and touch the blu and blk if it lights you have ground and power.
no light on blue and white f14 and f12 blown.
if no ground it can only be one more thing that is the control head itself.
have them ship you one for 35 bucks worth the try may sure it is knob type or pushbutton be clear when ordering part, you said you turned the knob this listing is for the knob type, go to begining and choose pushbutton.
do not give up now i and you have spent alot of time on this , we can succed