From the Ford 2001 Service Manual
DTC : P1633 - Keep Alive Power Voltage Too Low
Indicates that the Keep Alive Power (KAPWR) circuit has experienced a power interrupt.
Possible Causes :
Open KAPWR circuit
Intermittent KAPWR Circuit
Diagnostic Aides :
This is from the Service manual, I have not seen this myself, nor do I know how well the poss causes are.
The only part I see in the electrical diagram for the KAPWR ckt is on pg 25-9, the PCM. It is pin 55 ckt 729 red / white stripe.
If you don't know the PCM is located under the hood, pass. side, between the firewall, and the battery ( page 151-21, C174 )..
Sounds like something serious to me, the electrical manual gives no additional wiring locations for this, so it might be internal to the PCM.
Sorry it might not be much help.
Last edited by SSCULLY; 11-09-2002 at 11:33 PM.