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Welcome, I'm Chris (aka Moose) I'm an independent contractor here at Just Answer.
If the lights are not coming on then the transfer case should not be engaging. Does it engage into low range resulting in low gear to the rear axle?
Are there stored 4x4 trouble codes?
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Thanks, ***** ***** come on when the transfer case shifts, then the front axle locks in. We need to test the switch on the transfer case that tells the GEM module the transfer case position.
Verify the sensor and transfer case is a good no resistance ground to the frame.
4x2 no wires to the switch are grounded.
4x4 high gray wire is grounded
4x4 high the gray and light blue/black wires are grounded.
Test the switch as well as remotely ground these wires to see if the GEM is getting the signal and turning on the 4x4 lights.
It faces the front axle near where the manual linkage connects.
That is correct.
You can check either the wire while connected or the pins on the sensor while not connected to confirm the switch is working right.
Your test indicated the switch is bad, but it appears you have a GEM module issue as well since you were not able to get the 4x4 lights on with remote grounding. Your next step will be a new switch installed. Do you need to see a diagram on how it works?
I doubt the switch is in stock much less sold aftermarket.
Thanks, ***** ***** have to get the GEM to turn on the lights. It will only turn on the lights when it realizes you have shifted the transfer case. Once the lights come on, the GEM should command the front axle to engage. So now we need to see if these 2 signal wires going to the GEM are broken, and if not then its the GEM that is faulty. If diagrams from Ford would better assistance I can upload those in private contact since everything written so far here is public.
The next test is to access the GEM module connector wires. Disconnect the 2 wires prior tested at the switch, and unplug the switch. OHM test these wires at both ends and see if there is no resistance.
You are unplugging the GEM and sensor and testing the wires to see if they are broken. Both wires should have no resistance and no continuity to each other, power, or ground.
There are no voltage tests on these wires needing to be done.
Part of the GEM could fail and other sections of it still work fine, the battery saver relay test alone does not confirm the GEM is good.
Let me know once you have completed these wire tests, then we have about a dozen more tests we can do from the Ford pinpoint test for this concern.
You will have to remove the fuse box to get to the GEM.
Next is to see if the GEM module has any codes stored. There are 25 tests in all. If there are codes we can avoid doing 11 of them. Just a heads up the post will time out on the 14th.
The site gives us 7 days to get a post rated. If that time passes then the post is removed from our active list. Which means you reply and I never see it because the post was deemed not resolved or rated. That is the way the site is setup, which i am not an employee of, they collect your deposit on the 1st day your here. Techs are not paid from that till a rating is done.
It appears you closed your post, so thanks for letting me try to help, best of luck to you.