No air or heat is blowing out of my 1998 F-150. I need a GEM module also. could that be the cause of no air or heat.

What fuse blows ? The four wheel drive switch is a input to the GEM - generic electronic control module , low voltage ! There are a few different relays, a shift motor on the transfer case . There could be DTC'S - diagnostic trouble codes stored in the GEM module . You can find free wiring diagrams at http://www.bbbind.com/free_tsb.html Do you know how to do basic automotive electrical testing ? When you turn the switch to engage the 4X4 , the GEM see's that input an then energizes a relay to engage the 4X4 . Knowing which fuse blows would cut down on the guess work !

Fuses are listed here
* = maxi fuse
1*=50A I/P fuse panel
2*=40A blower motor relay
3*= 50A 4 wheel ABS module
4*=20a Main light switch-Instrument cluster
5*=50A Ignition switch, starter relay
6*=20A Transfer case relay
7*= NOT USED
8*=20A Auto Ride Control Switch/on off switch
9*=40A Auto Ride Control relay
10*=30A PCM power relay
mini fuses
1=10A A/C relay
2=20A Aux power point
3= not used
4=15A Fog lamps-Daytime lamps
5=10A Air Bag diagnostic monitor
6=10A Powertrain Control Module (PCM)
7=30A 4WABS module
8=30A PCM relay
9=20A Fuel Pump relay and RAP module
10= 15A Horn relay
11=15A Park Lamp relay-Main Light Switch
12=30A Main light switch--Multi Function switch
13=15A Heated O2 sensors, EGR Vacuum Regulator, EVR solenoid,Camshaft position (CMP) Sensor,
Cannister Vent Solenoid, A4LD Auto Transmission
14=30A Generator-Voltage regulator
Interior fuse panel (mini fuses)
1=7.5A Power mirror switch
2=7.5A Blower motor relay,PAD module,Air Bag diagnostic monitor
3=7.5A Trailer tow connector
4=10A Left headlamp
5=10A Data link connector (DLC)
6=7.5A Air bag diagnostic monitor, Blower motor relay, Passive deactivation Module (PAD)
7=7.5A Trailer Tow connector
8=10A Right headlamp, Daytime running lamps (DRL) module, Foglight relay
9=7.5A Stop Lamp switch
10= 7.5A Speed control-amplifier assembly,Brake pressure switch, Generic electronoc Module (GEM)
Shift lock actuator, Blend door actuator, Main light switch, RABS resistor, A/C heater assembly
Flasher
11= 7.5A Instrument cluster, Main light switch, RABS resistor
12= 10A Power window relay, Washer pump relay
13= 20A Stop lamp switch, Brake pressure switch
14= 20A Rear Anti Lock Brake system (RABS) module
**10A 4WABS module**
15=7.5A Instrument cluster
16= 30A Windshield wiper Motor, Wiper Hi-lo relay, wiper run/park relay
17=7.5A Cig lighter
18=15A Drivers unlock relay-All unlock relay
19=25A PCM power diode
20=7.5A RAP module GEM module, Radio
21=15A Flasher (hazard)
22=20A Aux power socket
23=15A Turn signals
24===not used
25= 7.5A GEM module, Instrument cluster
26= 10A Battery saver relay, Electronic Shift relay, Interior lamp relay
Power window relay,Electronic shift control module, transmission control
27=15A Switch,DRL, Backup lamp switch, DTR sensor,Instrument illumination dimming control module
Dome/map lamp, GEM,electronic shift,Interior lights,Glove box lamp and switch
28=7.5A GEM module-Radio
29= 15A Radio
30=15A Park lamps, trailer Tow relay
31===not used
32=10A rear blower
33=15A Headlamps, DRL module, Instrument cluster
34=7.5A Rear integrated control panel, CD
35=10A RABS test connector
36=7.5A CD, rear integrated control panel, memory seat,

i copied this off another post hope this helps

Ford , Lincoln , Mercury in that era called a GEM generic electronic module .
The generic electronic module (GEM) constantly monitors its subsystems for concerns. If a concern is found in one of the subsystems, the GEM will record the concern in the form of a diagnostic trouble code (DTC).
The ignition switch position is very important to the GEM function. Often times, erratic or unexpected GEM function can be traced to problems with these GEM inputs.
The GEM controls the following features:

• Wipers/washers (front/rear).
• Warning chimes.
• Battery saver.
• Illuminated entry and courtesy lamps.
• Driver power window.
• Accessory delay.
• 4-wheel drive.
• Heated back lite/mirror.

Generic Electronic Module (GEM) C239
Behind center of I/P CAUTION: Prior to removal of the module, it is necessary to upload module configuration information to scan tool. This information needs to be downloaded into the new module once installed. For additional information, refer to Section 418-01 .
CAUTION: Electronic modules are sensitive to electrical charges. If exposed to these charges, damage may result.

There is a climate control module in the head liner of that vehicle. IT needs to be checked or replaced

Central Junction Box / cab fuse panel Fuse 15 ( 5A ) feeds the GEM Module

A leaking windshield ( lower left hand corner ) can cause water to get on the back of the CJB, and corrode the pins to the GEM.

go to the ford lincoln mercury website and enter you year, make, model of your vehicle. It will let you download a pdf version to your computer. then open the document and go to page 135. this is free don't pay for something you shouldn't, you already got the vehicle. this is just information. Fuse Location,Fuse Amp,Description
1) 25A Audio
2) 5A Clock, Overhead Trip Computer, Electronic
Automatic Temperature Control (EATC),
Powertrain Control Module (PCM), Cluster
3) 20A Cigar Lighter, OBD-II Scan Tool Connector
4) 15A Autolamp Module, Remote Entry Module,
Mirrors, Memory Module, Adjustable
Pedals, Air Suspension Switch
5) 15A AC Clutch Relay, Speed Control Module,
Reverse Lamp, EVO Module, Climate Mode
6 5A Cluster, Overhead Trip Computer, Compass,
Steering Sensor, Brake Shift Interlock
Solenoid, Air Suspension Module, GEM
Module
7 5A Aux A/C Blower Relay, Console Blower
8 5A Radio, Remote Entry Module, Cell Phone,
Clock, GEM Module
9 — Not Used
10 — Not Used
11 30A Front Washer Pump Relay, Wiper Run/Park
Relay, Wiper Hi/LO Relay, Windshield Wiper
Motor, Rear Washer Pump Relay
12 — Not Used
13 20A Stop Lamp Switch (Lamps), Turn/Hazard
Flasher, Speed Control Module
14 15A Rear Wipers, Running Board Lamps,
Battery Saver Relay, Interior Lamp Relay,
Accessory Delay Relay (Power Windows,
Flip Windows, Audio)
15 5A Stop Lamp Switch, (Speed Control, Brake
Shift Interlock, ABS, PCM Module Inputs),
GEM Module
16 20A Headlamps (Hi Beams), Cluster (Hi Beam
Indicator)
17 10A Heated Mirrors/Rear Window Defroster
Indicator
18 5A Instrument Illumination (Dimmer Switch
Power), Clock (Dimmer)
19 — Not Used
20 5A Audio, Four Wheel Air Suspension (4WAS)
Module, Memory Module, GEM Module,
Digital Transmission Range Selector
21 15A Starter Relay, Fuse 20
22 10A Air Bag Module
23 10A Electrochromic Mirror, Aux A/C, Heated
Seats, Trailer Tow Battery Charge,
Turn/Hazard Flasher, Console Blower Door
Actuator
24 10A Climate Mode Switch (Blower Relay),
EATC (via fuse 7), EATC Blower Relay
25 5A 4 Wheel Anti-Lock Brake System (4WABS)
Module
26 10A Right Side Low Beam Headlamp
27 5A Foglamp Relay and Foglamp Indicator
28 10A Left Side Low Beam Headlamp
29 5A Autolamp Module, Transmission Overdrive
Control Switch
30 30A Passive Anti Theft Transceiver, Cluster,
Ignition Coils, Powertrain Control Module
Relay
31 10A Rear Integrated Control Panel (Audio), CD
Player, Cell Phone
Relay 1 — Interior Lamp Relay
Relay 2 — Battery Saver Relay
Relay 3 — Rear Window Defroster Relay
Relay 4 — One Touch Down Window Relay
Relay 5 — ACC Delay Relay

hope this helps.

A shift release solenoid is to blame causing this problem. It is shorted out and needs to be replaced

Fuses are listed here

* = maxi fuse

1*=50A I/P fuse panel
2*=40A blower motor relay
3*= 50A 4 wheel ABS module
4*=20a Main light switch-Instrument cluster
5*=50A Ignition switch, starter relay

6*=20A Transfer case relay
7*= NOT USED
8*=20A Auto Ride Control Switch/on off switch
9*=40A Auto Ride Control relay
10*=30A PCM power relay

mini fuses
1=10A A/C relay
2=20A Aux power point
3= not used
4=15A Fog lamps-Daytime lamps
5=10A Air Bag diagnostic monitor
6=10A Powertrain Control Module (PCM)
7=30A 4WABS module
8=30A PCM relay
9=20A Fuel Pump relay and RAP module
10= 15A Horn relay
11=15A Park Lamp relay-Main Light Switch
12=30A Main light switch--Multi Function switch
13=15A Heated O2 sensors, EGR Vacuum Regulator, EVR solenoid,Camshaft position (CMP) Sensor,
Cannister Vent Solenoid, A4LD Auto Transmission
14=30A Generator-Voltage regulator


Interior fuse panel (mini fuses)

1=7.5A Power mirror switch
2=7.5A Blower motor relay,PAD module,Air Bag diagnostic monitor
3=7.5A Trailer tow connector
4=10A Left headlamp
5=10A Data link connector (DLC)
6=7.5A Air bag diagnostic monitor, Blower motor relay, Passive deactivation Module (PAD)
7=7.5A Trailer Tow connector
8=10A Right headlamp, Daytime running lamps (DRL) module, Foglight relay
9=7.5A Stop Lamp switch
10= 7.5A Speed control-amplifier assembly,Brake pressure switch, Generic electronoc Module (GEM)
Shift lock actuator, Blend door actuator, Main light switch, RABS resistor, A/C heater assembly
Flasher
11= 7.5A Instrument cluster, Main light switch, RABS resistor
12= 10A Power window relay, Washer pump relay
13= 20A Stop lamp switch, Brake pressure switch
14= 20A Rear Anti Lock Brake system (RABS) module
**10A 4WABS module**

15=7.5A Instrument cluster
16= 30A Windshield wiper Motor, Wiper Hi-lo relay, wiper run/park relay
17=7.5A Cig lighter
18=15A Drivers unlock relay-All unlock relay
19=25A PCM power diode
20=7.5A RAP module GEM module, Radio
21=15A Flasher (hazard)
22=20A Aux power socket
23=15A Turn signals
24===not used
25= 7.5A GEM module, Instrument cluster
26= 10A Battery saver relay, Electronic Shift relay, Interior lamp relay
Power window relay,Electronic shift control module, transmission control
27=15A Switch,DRL, Backup lamp switch, DTR sensor,Instrument illumination dimming control module
Dome/map lamp, GEM,electronic shift,Interior lights,Glove box lamp and switch
28=7.5A GEM module-Radio
29= 15A Radio
30=15A Park lamps, trailer Tow relay
31===not used
32=10A rear blower
33=15A Headlamps, DRL module, Instrument cluster
34=7.5A Rear integrated control panel, CD
35=10A RABS test connector
36=7.5A CD, rear integrated control panel, memory seat, Message center Attached images __________________

I think you may have lost communication with the GEM module. Only dealer can reestablish.
Generic Electronic Module (GEM) Removal and Installation

1. CAUTION: Prior to removal of the module, it is necessary to upload module configuration information to the appropriate diagnostic tool. This information needs to be downloaded into the new module once installed. For additional information, refer to Section 418-01 .
   CAUTION: Electronic modules are sensitive to static electrical charges. If exposed to these charges, damage may result.
   
2. ---------------------------------------------------------------------
   

Module Controlled Functions NOTE: Prior to removal of the generic electronic module (GEM), it is necessary to upload module configuration information to the diagnostic tool. This information needs to be downloaded into the new module once installed. For additional information, refer to Section 418-01 .
NOTE: Electronic modules are sensitive to electrical charges. If exposed to these charges, damages may result.
The generic electronic module (GEM) is the only multi-function module on this vehicle.
The GEM constantly monitors its subsystems for concerns. If a concern is found in one of the subsystems, the GEM will record the concern in the form of a diagnostic trouble code (DTC).
The ignition switch position is very important to the GEM functionality Erratic or unexpected GEM functions can often be traced to problems with these GEM inputs.
The GEM controls a variety of systems:

• instrument cluster warning indication and chimes
• interior courtesy lamp control
• automatic headlamp control
• daytime running lamps (DRL)
• wiper and washer (front only)
• heated rear window
• one-touch down power window
• delayed accessory
• power door locks (including SMART, autolocking and luggage compartment lid release)
• remote keyless entry
• perimeter anti-theft

you need to have your GEM module reconfigured after battery disconnect. It controls many functions. It may have also been damaged during battery change due to a voltage spike. Dealer can test it. Call a dealer service dept and describe symptoms and see what they say.

Module Controlled Functions NOTE: Prior to removal of the generic electronic module (GEM), it is necessary to upload module configuration information to the scan tool. This information needs to be downloaded into the new module once installed. For additional information, refer to Section 418-01 .
NOTE: Electronic modules are sensitive to electrical charges. If exposed to these charges, damages may result.
The generic electronic module (GEM) is the only multi-function module on this vehicle.
The GEM constantly monitors its subsystems for concerns. If a concern is found in one of the subsystems, the GEM will record the concern in the form of a diagnostic trouble code (DTC).
The ignition switch position is very important to the GEM functionality Erratic or unexpected GEM functions can often be traced to problems with these GEM inputs.
The GEM controls a variety of systems:

• instrument cluster warning indication and chimes
• interior courtesy lamp control
• automatic headlamp control
• daytime running lamps (DRL)
• wiper and washer (front only)
• heated rear window
• one-touch down power window
• delayed accessory
• power door locks (including SMART, autolocking and luggage compartment lid release)
• remote keyless entry
• perimeter anti-theft

-------------------------------------------
Principles of Operation
The generic electronic module (GEM) constantly monitors its subsystems for concerns. If a concern is found in one of the subsystems, the GEM will record the concern in the form of a diagnostic trouble code (DTC).
The ignition switch position is very important to the GEM functionality. Erratic or unexpected GEM functions can often be traced to problems with these GEM inputs.
----------------------------------------------------------------------------