Hi
I have a 1998 F150 4x4 (currently only a 2x4). I have done some research on the site to see how the 4x4 selection system works. I have discovered that the two solenoids on the firewall always have 12 volts to them no matter which way I move the rotory selector switch. It is my understanding that if I move the selector switch it should change the power from one solenoid to the other. Upon furthur checking I thought I would check all fuses for power and continuity. All fuses had continuity so all were good. However I discovered that one of the 5 amp fuses that is labelled for the GEM has no voltage on either side of the fuse in the fuse panel inside the cab of the truck. I understand this GEM does control the 4x4 ESOF. How do I get power to this fuse holder.. I would of thought the power would go from the fuse panel first them out to the device . I checked the fuse and it tested good. I even stuck my tester into the socket of the fuse holder and still no voltage registered. Any help would be appreciated. I don't know where to go next.

 

How about which 5 A fuse are you talking about ?

 

It is fuse number 15 in the cab and is controlling the Generic Electronic Module. Hope this helps.

 

Fuse # 15 is fed by the Power distribution box ( under hod ) fuse # 22, 50 A.

The PDB also feeds a lot more then just that ( cab fuses # 1,2,3,4,12,13,14,15 ) It is safe to say that if your interior lights or flashers work, that PDB Fuse #22 is good ( fuse #1 & # 14 ).

The ESOF section refers to fuses Junction box 13 & 23 and PDB 17 and cover the GEM and PCM.

Does the truck run with this fuse not working ?

Fuse #15 only is referenced in the cell 59-1, and one side should be hot at all times.

Are you sure you are using a good ground to test to ?

 

The truck runs fine with this fuse not working. I am fairly certain that the ground I am using is good as it works with all the other fuses i am checking .
I just finished checking the entire fuse panel again. I have discovered that circuit 16, 20, 26, 27, 28 have no power at either side of the fuse and the fuses have continuity when i remove them and check them. I checked under the hood in the Power distribution box and discovered all fuses have 11.97 volts dc on either side of the fuse so this tells me all fuses there are good and that power is being sent to the inside fuse box. The funny thing is I notice that fuse 16 controls the insturment cluster, daytime running , Hi beam etc.. All of these are still working on the truck but I cannot get it to show me voltage at the fuse box. I even took out the fuse and inserted my probe on my meter into each side of the fuse holder socket and the other end to a bonified ground and still no power. I am very perplexed. At one point I had 6 volts on Circuit 16 but I can't duplicate that. I am an electrician and enjoy troubleshooting but this one has me baffled. Perhaps I should stick to AC voltage. Any more insight would be greatly apppreciated. Cheers Dan

 

Quick test that I can think of. Test on the pin on the back of the fuse on Fuse # 16, and make sure it shows no power still, while you have the parking lamps on.
When you verify there is no power at the fuse, and the instrument illumination is working, pull the fuse, and see if the instrument illumination goes dead.

 

Hi
I tried that. When you say the back of the fuse you mean the metal tabs on either side of the 20 amp marking correct. If this is correct placement I tried it and verified no power on either pin and had lights on in dash for illumination. I removed said fuse and lights continue to work. Wierd eh.

 

Yep, the fuse pins that extend to the back of the fuse

Side 1, where power comes in :


side 2, where power is after the fuse element


Does your truck have DRL ?

The instrument illumination is on Fuse # 16 without DRL, with DRL it is on Fuse # 18, and the Instrument illumination diagram only shows it on fuse # 18 ( via PDB Fuse # 7 )

If you do not have DRL, and pull fuse 16, and it still worked, try the test with fuse # 18. I find it strange that all those fuses do not have power, but the items still work.
Can you double check the orientation that you are using on the Cab fuse panel for the testing ( making sure you are on the correct fuse ).

Also, can you take a look up behind the main headlamp switch, and see if there is any modification to the wiring ( fog lamp modification jumper, etc ).

Without DRL, and you pull the fuse, the instrument illumination should go dead, else there is something very wrong.

 

Hi
Me again. I do have daytime running lights and checked fuse 18 and does have power and when I do remove it the dash lights go dead as you said they would. I still have no power to either side of fuse 16. As for the ones I checked last night #20,26,27,28 they appear to have power again. I am getting frustrated with this. Where does the power come from to fuse 16. Is it a relay or something perhaps. I have the dash all pulled apart now I am committed. thanks for all your help you sure do know your Fords. Circuit #20 also has no power to either side. My appolagies but as for the others they now do.

 

Power for Fuse #16 comes from the MFS ( multi function switch ), via the main headlamp switch, from PDB ( engine compartment ) Fuse # 8.

PDB Fuse # 8 --- main headlamp switch----- MFS -------- JB Fuse #16---high beams ( and instrument panel high beam indicator lamp ) and the DRL module.

JB Fuse # 20, There is a note that this is only with the Manual transmission.
Shows JB Fuse # 21 to the Clutch Pedal position switch to JB Fuse #20.
JB Fuse #21 is fed from the ign switch ( start position ) via PDB Fuse # fuse #20, 50A.

Also still have JB fuse # 15 dead ( ? ) , as well as the 4x4 functions.

The 4x4 fuses are :
JB Fuse # 13 ( through Brake Pedal Position Switch )
PDB Fuse # 17 ( Transfer case shift relay ( L2H and H2L )
JB Fuse # 23 ) power to xfer case relay, controlled by the GEM on the ground side. Also the 4x4 disconnect solenoids that you talked about.
- These have power to them any time the key is in the run position. The GEM controls ground to them. ( just got back around to the actual thread problem back in post #1 )

 

Hi
I have gone over everything once more. I have power to all fuses in Jb in cab except for #16 and #20 and #21 I have no fuse for 17 in my owners manual it says not used. As to your last post my truck is automatic. It is starting to look like maybe my owners manual is telling me that these fuses control something else perhaps. The mechanic that did some work on my truck a while back says that it was made in Nov of 1997 but is called a 1998.
Could this be the confusion.. It is starting to look like it might just be a bad vacuum solenoid. You mentioned that they both have power on them at all times and then you select the 4 hi and that shorts out the proper solenoid and allows only one to apply vaccum.

My Manual says for the fuses that have no power to them they control the following:

#16 - Instrument cluster (W/O DRL), Daytime Running Lamps (DRL) Module,
Hi Beam Headlamps(Power Supplied through Multi-Function Switch)

#17 - Not Used

#18 -Park Lamp Relay, Trailer Electronic Brake Controller, Main Light Switch,
Trailer Tow Run Relay, Front park/turn lamps, Licence lights, stop/park/turn
lamps/tail/side marker lamps(power supplied through Main Light Switch)

#20 - powertrain Control Module, Generic Electronic Module/ Central timer Module

With thanks to you we have discovered that Hi beams drl is controlled from fuse #18 would that mean that #16 may not be used on my truck as well as
#20 and #21 because it is automatic. ? How about the rotary swith 2i, 4hi and 4lo. No illumintaion on these could this be the root of the problem?

 

The 1998 owners manuals left something to be desired. Taking a look at a 1997 OM might help ( some times ).
Mfgr date of NOV-97 would make it a 1998 MY truck ( production starts the AUG the year prior, ~ SEP is new MY time ).
There is an engine mini fuse panel in the 1998 that is not documented in the 1998 OM, need to look at a 1997 to find it.

now that I look at the picture, there is a 5 A PCM fuse in there, that could be where the PCM power is from, not Fuse # 15 ??



Here it is without the cover on it


The bad vacuum could be it, I think I have seen that one before. Might be in the transmission section ( I don't get much trolling time over in engines & Trans ).

now that I am awake, let me try to explain JB Fuse # 16 a bit better. Until you have the main headlamp switch in the head position, and the MFS pushed forward, or with the MFS pulled back in FTP mode, JB Fuse # 16 will be dead on both sides.

The illumination to the selector switch is via the Instrument panel illumination circuit, PDB Fuse # 7 to the main headlamp switch, then to JB Fuse # 18 ( along with the other things you noted ). JB Fuse # 18 will be dead until you turn on the main headlamp switch to either park or head positions.

Sorry about taking 2 days to remove my head from my rear. the Engine mini fuse panel ( documented in the 1997 OM ) and the poor explanation on the JB Fuse # 16.

 

Hi
I found that fuse panel in the engine compartment the 5 amp fuse is good so it is not the problem. Could it be the rotary selector switch as i said it has no lights on it in any of the positions. Does this tell the gem to short out the solenoids under the hood. I checked them again and the voltage is always 11.97 volts dc constant no matter which position I put it in. Just a thought.

 

The no lights on the selector switch illumination is a different circuit vs the 1 of 3 resistance values to the GEM, to tell what position the GEM should move to.

could be the bulb ( LED ) behind it as well.

The 4x4 switch gets voltage from the GEM, passes it through either a 3.9 K, 1.1 K or 360 ohm resistor, and passes it back to the GEM. Depending on what the return voltage is, tells the GEM what should be operational ( 2H, 4H, 4L ).

The GEM then triggers ground on the correct coil, to do something ( L2H or H2L ), along with the transfer case clutch relay, to activate the magnetic clutch coil.

The 4x2 center axle disconnect solenoid and 4x4 center axle disconnect solenoid get ground from the GEM as well.

For the 4x2 one
+ 12 V in run position white w/ light blue stripe wire ( hot any time the truck has the key in the run position, direct wire to JB Fuse # 23. )
gnd = gray w/ black stripe wire ( when GEM calls for it )

For the 4x4 one
+ 12 V in run position white w/ light blue stripe wire ( hot any time the truck has the key in the run position, direct wire to JB Fuse # 23. )
gnd = red wire ( when GEM calls for it )

The GEM reads the speed from the VSS, and only selects 4L when the speed is below 5 kph. I don't know if it will do anything at a stand still, I would guess it would.

GEM also has inputs from the transfer case to know the position of the transfer case motor.

This just came to me, were you ( or did you ) have the secondary cruise control deactivation switch recall done ?

Another member had his GEM toasted by what he said was a recalled truck. Don't know how, but looking over this forum section, saw this one from few days back.

https://www.f150online.com/forums/el...ipers-etc.html

 

Hi
I did have that recall done i believe about two years ago. It was a recall on the cruise controll where if left could cause a fire. They disconnected the cruise and a later date replaced defective parts. Shorltly after this the cruise quit working and they denied it was caused by them. After a little discussion with the service manager they were more than happy to correct the problem. Cruise works fine. I tested the operation of the transfer case and it has drive to the front shaft when i engage the 4x4 switch but the two solenoids always have 12 volts no matter which position the switch is in. If it shorts one of them to ground I should not have voltage at the connector correct? Still have no power on fuse #20 on either side. Fuse that controls pcm/gem/cmt. Not sure if you mentioned it gets power when something else is on. So many things in my head. Thanks again. This sure is a wonderful site to have to assist people.