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Q: What runs 2007 FX4 4x4, GEM module or VSM on 2007 Ford F-150

2007 Ford f150 FX4. Electrical problem with 4x4. Sometimes works sometimes not. Replaced solnoid still nothing. No lights on dash indicating 4x4 or sound of transfer case ingaging. Just for fun I tried it on my way home tonight I could hear the transfer case and had lights on dash...4x4. Sounds electrical. Just moved from California where it only rained. Did not use 4x4 for two years. Moved to Idaho in June and needed 4x4 but got nothing when I flipped switch. Messed with fuses none bad. Checked # 11, 28, and 29, all good. Put fuse panel back together then I had a reading light start working that has been out for about 1 year. It only worked for1 day, now doesn't work again. Does my truck use a GEM module or VSM to work the 4x4 system? Where are they located? Thank you.
What seems to make the problem better or worse? Nothing
How long have you had this problem? Haven't used 4x4 for 2 years now living in snow country
dome reading lights work, ford, f 150
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If you have the electrical 4x4 system, the Powertrain Control Module (PCM) controls the whole show. The 4x4 selector switch talks directly to the PCM. The PCM controls the 4x4 transfer case shift motor via 2 relays in the AUX Relay 1 box. Those relays are powered by Fuse 111 30 amp in the Central Junction Box. There is an encoder in the transfer case that reports the tx case position to the PCM.
To test the selector switch, check the resistance between the 2 dark blue wire pins with the harness unplugged. Pins 2 & 3. The resistance should change at each switch position. There should not be an open or a short.

This I found in the manual:
The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to synchronize the front driveline. When the mode select switch (MSS) on the instrument panel is turned, the 4WD module (PCM) activates the electromagnetic clutch and powers the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the 4WD module (PCM), power to the shift motor will be removed. When the transfer case front and rear output shafts are synchronized, the spring-loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle integrated wheel ends (IWEs) are engaged and the electromagnetic clutch is deactivated.
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