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Discussion Starter · #1 ·
my 4wd is not working.. i went to put it in 4lo a week or so ago.. it never engaged so i just shut off the truck to load a tv for a friend.. it usually kicked in after a sec but i didnt want to wait.. so with it not being in 4lo i didnt think of takin it out.. drove a lil bit on 75 then noticed the shifter was still in 4lo but it wasnt in 4wd.. now it will not do anything.. im not getting power to my on the fly switch. no power that i can tell to the transfer case.. checked the two fuses and they are good.. what to do now.. any ideas?

early 99 sd shift on the fly
 

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Could be the switch or motor. Attached is a PDF of the wiring diagram. Does 4hi work?
 

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vacuum problem maybe????
 

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sounds like a vaccum problem...
 

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GEM. electronic control module was bad on mine. 4wd was really finicky for months, then finally quit all together. replaced that module and been great ever since... btw that was last time i ever took my truck to a dealer. they got me on that one.
 

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Where is this GEM located?
 

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Under the dash, behind the fuse bax.
 

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Discussion Starter · #9 ·
not a vacume problem did away with that stuff a while back.. went with mile markers. and capped the lines..

i might be lookin for the GEM once i get my truck back.. that sounds like a good chance cause mine was finicky for awhile too..
what did the GEM cost

thanks guys.. let ya know what the verdict is.. any other ideas let me know..
 

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Before you get a new GEM, check all of the wires for continuity. Check the resistors on the switch and relays as well. I had a broken wire in the harness a few months ago.
 
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