4x4 no light and switch doesn't work

90f250

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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.

Sent from my SM-N960U using Tapatalk


Tried this as well this morning and still nothing
 

greenskeeper

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Yes EVERY single fuse and relay all check out just fine. Both under dash and under hood.

Ok so my next step would be to probe the harness at the PCM and see if you've got 12v going to the PCM
 

90f250

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Ok I probed every pin and got nothing! From the picture I pulled up I should have at minimum a constant hot wire. Number 55 or 56 or something.. and then with the key on i should have power at 71 i think it was it said. Regardless of key on or not i have no power on any pin
 

greenskeeper

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I think there's a fusible link somewhere on the big harness?
 

90f250

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I think there's a fusible link somewhere on the big harness?

I'll have to search for that. On the bright side my 4x4 is fixed. Someone had black tape on the white/blue tracer and the solid purple wire that come from the switch and go to the gem. Well. I took the tape off and found the white/blue wire wasnt even connected. So I spliced it back together and walla.. 4x4 works now. So my problem is still that the truck wont start. Lol. No wts fuel pump or tach.
 

greenskeeper

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I'll have to search for that. On the bright side my 4x4 is fixed. Someone had black tape on the white/blue tracer and the solid purple wire that come from the switch and go to the gem. Well. I took the tape off and found the white/blue wire wasnt even connected. So I spliced it back together and walla.. 4x4 works now. So my problem is still that the truck wont start. Lol. No wts fuel pump or tach.

Wow...that stinks after all this is was a bad connection.

You could back-track to the fuse controlling the PCM and check for power there.
 

90f250

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Wow...that stinks after all this is was a bad connection.

You could back-track to the fuse controlling the PCM and check for power there.



I know right??!! But in all seriousness every fuse and relay are good and have power to both sides. I've got to be missing something simple somewhere
 

greenskeeper

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I know right??!! But in all seriousness every fuse and relay are good and have power to both sides. I've got to be missing something simple somewhere

is there anti-theft installed on the truck?

What happens when you disconnect the batteries and reinstall the original PCM and GEM modules?
 

DaveBen

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This sounds like a bad fuse-link. Try tracing the hot wire back to the battery. If it is a fuse-link you can replace with a wire and add a fuse to that wire.
 

90f250

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This sounds like a bad fuse-link. Try tracing the hot wire back to the battery. If it is a fuse-link you can replace with a wire and add a fuse to that wire.


That's the issue, tracing THAT wire, it's all in the factory plastic looms and tape and not much rrom if any to do anything
 

DaveBen

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You could replace the wire harness. I think lmctrucks.com has them. This is not an easy thing to find and it is not easy or cheap to fix. Is it worth it to you?
 

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