Ford: the vents defrost etc do not work on 96 ford explorer, voltage rectifier, amp fuse

Question
QUESTION: the vents, defrost etc do not work.  we replaced the blower motor and when we looked at the old one it was locked up and was hard to turn. when hooked to the battery it heated up the wires.  the new one works when hooked to a battery but when installed does not.  when the blower is hooked to its harness and an alternate ground wire is run directly to a metal bolt  the blower will work on high. could the old blower have shorted out wires or is there something else we can look at.  if it is wiring is there a specific area that would have been affected.

ANSWER: check the heater fan switch, hooking into a different (better) ground wont hurt it at all. test the connectors with a volt meter, but odds are its the switch.

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QUESTION: we  tested the wire harness with a volt meter and it said it was at 8.5volts.  When we run a new  ground  the fan runs on high and there is no other options. it will not turn off.  where do we find the heater fan switch?  if it is not the switch it we were going to rerun the ground with a 20 amp fuse but then we will have to keep the fan on at all times.   thanks for your help

Answer
first fusing a ground is pointless. the two things you want to look at replacing are the voltage rectifier,which makes the fan have low and medium speeds it is on the blower housing box or close by, track the wires from the fan, its usely a small back box with 3 or 4 wires hooked into it, with the same harness as the fan. replace this, and re try. 8.5 volts is way too low, check to make sure you have a solid 12+vdc coming in to the switch. should be at 30 amps.