Electric shift 4x4 switch problem (non-hardcore) - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 03-20-2017, 03:39 AM   #1 (permalink)
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Electric shift 4x4 switch problem (non-hardcore)

I have a late 04 F150 with the electric transfer case. It's been giving me trouble shifting into 4x4 and I have done all the normal guess repairs (TC shift motor, IWE solenoid, checked fuses/relays) and finally started troubleshooting for real. I found the resistance in the dash switch (MSS) is bad in the 2h position. It's supposed to be 620 and I have an open. The 4h and 4l readings are right in spec.

Does anyone have experience with these? I'm worried that the $100 switch was possibly ruined by some other problem I haven't found yet. Should I put the new switch in disconnect the PCM to reset and try it or should I expect another problem caused the switch to fail? Would the PCM see the bad switch and set a code that would disable all the 4x4 modes? Fail safe in 2H?

If I use a battery to drive the motor into 4h with the switch already there it will stay in 4h until I select 2H. It shifts back to 2H like normal and then won't work with the switch again. When 4h is selected with the switch the CW relay clicks but the TC motor doesn't shift. I tried switching the CW and CCW relays but no change. All wires look visually intact but I haven't went thru each one with the ohm meter yet.
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Old 03-20-2017, 05:18 PM   #2 (permalink)
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For anybody watching my fear was correct. Must have a short somewhere. New switch fried.
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Old 03-20-2017, 11:07 PM   #3 (permalink)
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I have known a lot of people with different problems switching who have all done the following, including me.. I dont understand why it helps or works.. just that I tried it too and it was fine afterward.. you can look up the discussions on OLD fordtruckworld.com forums.. anyways

take the plastic cover in the engine compartment (pretty much center of firewall), thats covering a bunch of "stuff which I know little about" and spray the hell out of it with wd40.. just try it and see what happens..

yes it was a pain taking off the cover, balancing over the engine.. but for some miracle it works for lots of people..
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Old 03-21-2017, 07:01 PM   #4 (permalink)
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I'll take a quick look for you at work tomorrow (30 years as a Ford tech) I've seen tons of problems with the main harness that runs from the engine compartment to the back of the truck but I'm not sure where that harness runs. I've also seems lots of corrosion in the areas under the threshold trim there's a channel there where the wiring harnesses run that holds moisture and it gets into the harness. HTH
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Old 03-31-2017, 04:41 PM   #5 (permalink)
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For anyone that might have been following the problem was in the relay box mounted on the drivers fender. I ended up taking it to a shop and they found it. They said there was corrosion in the connections that was messing with the grounds mostly. I'm not surprised, seeing that this oriented so any water that comes through the hood would run down in to this box . I had pulled the relays out of there but you couldn't see any problems from the top. It was not allowing the CW relay to get good contact and stay closed.

If you are testing a 4wd switch, beware that the ford FSM calls out a resistance of 620 ohms in the 2hi position and other specific values for the other 2 positions. My switches matched the other 2 perfectly. My switch shows open in 2hi but works as normal. It was never the problem. Both switches, old and new read out the same.
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