4x4 no light and switch doesn't work

90f250

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Another update! According to the dealership I have the wrong gem module to begin with! So now I'm on the hunt for the correct one because I'm not paying 725 for it from them!
 

79jasper

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Totally possible someone else swapped it in the past, which is why someone had it on switches. Lol

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90f250

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New update: put in another gem according to the dealership the one my truck should have. Now my 4x4 light and lo range light come on WHEN I STOP CRANKING THE ENGINE. also, now my glow plug light doesn't come on and my truck doesn't start... so... what the heck am I missing
 

90f250

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All fuses and relays good. No rpm movement while cranking, no glow plug light, no start. But when I manually flip the relay for 4x4 and it engages 4x4 the light does come on in high and low and turns back off in 2wd... and still doesnt switch when the switch... this thing is getting real aggravating...
 

90f250

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Yea I just figured that out when I put the old gem back in just so I could drive my truck if I need to until I figure it all out... well.. old gem doesnt work now either. No wts, no 4x4, no cig lighter power... but now all the sudden for the first time since I've owned the truck, the vacuum pump kicked on
 

90f250

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I made sure to go back over fuses and relays and everything is good. There's literally no reason for it not to work with the old gem. It ran fine before
 

90f250

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Well, I dont think ford told me the correct gem first of all. Unless someone also swapped the entire fuse box. Both have date stamps of March of 99... and also now doesnt matter which gem I throw in, no power to pcm. Again, all fuses and relays are good. I just went back through and looked over all the wiring to make sure I didnt mess so.ething up, everything looks fine as well. Did this other gem module maybe fry my pcm???
 

90f250

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Well.. I pulled the computer out as well and tore it apart. Everything looks good no burnt anything no water damage absolutely nothing wrong... same with all 3 different gem modules I have. Everything is good. Fuse box looks and smells to be fine as well but I cannot actually take it all the way apart for some reason and I dont want to break it.
 

90f250

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I'm about to put full coverage on it and burn it to the ground.... I understand I dont have power to the pcm. But I cannot figure out why. Everything worked fine besides 4x4 with the old gem. Now I have no pcm power no matter what gem is in it. Yet all fuses and relays are good and all have power. I've traced wire after wire and to no avail. I pulled computer and pulled apart and checked it. I've taken out my hydra tuner. I've done EVERYTHING anyone has mentioned and then some. I cannot figure this truck out. I dont even care about 4x4 right now, I just want it to run!
 

79jasper

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If you swapped the pcm with a known good one (that matches pcm code) and still nothing, you have a wiring/relay/fuse problem.
Just for giggles, unplug the fuel heater, and swap the pcm relay.

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