| Make sure the vacuum hose between the pump component and the cable housing is not leaking/dry rotted. Then split the diagnosis between the two components of the under hood unit. You've already established that the vacuum pump runs, so we'll assume that will actually pull a vacuum. Using a different vacuum source, apply vacuum directly to the cable housing component and see if you can get retraction. If you can't, the internal diaphragm is probably shot. If you can get retraction, move onto the next step. If you can get the cable to retract independent of the pump and you can get the pump to run, but can't get the pump to retract the cable, then there's an issue with one or both of the two check valves in the pump assembly. Electrically check that each of the check valve 'plungers' operate. Ref the image from Step B. Apply +12v to pin 1 and then, separately, apply ground to pin 2 and then pin 3. The pump assembly should 'click' as ground is applied and removed. If both check valves operators click with power, open up the pump assembly housing and examine that the sealing/seating area of the check valve is clear of any debris or buildup. These are small circular membranes. There might be some foreign debris preventing them from holding vacuum. Both check valves have to hold to maintain vacuum in the cable housing component. Good luck.
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