99 & up 7.3L Power Stroke Engine and DrivetrainDiscussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.
Hey guys, I drove my brothers truck (2001 f250 diesel, 6 speed) to work this morning and noticed it was vibrating a lot. When I got to work I tried to spin in snow and realized it was in 44wd. The light is not on nor does it come on when I turn the switch to 4wd. It's not my truck so I'm not 100 percent sure the light works. any idea's where to start? I checked the 30amp fuse but can't find any relays for it.
You have two relays under the hood on the driver side near the firewall that control the shift motor on the t case, the relays are powered at all times and the gem module gives the ground when shifting in and out of four wheel drive.
If your problem is the same as what I've had happen to me on two different trucks the grounding wire going from the gem module to the relay gets a nick in the insulation and goes green thus no longer conducts.
You can jumper the ground to the relay to test my theory and if the t case shifts you know you've found the problem.
Get the wiring diagram so you know what wire to ground.
The wires that ground the relays are smaller dia than the power wires, I think the one that was bad on mine was a brown wire with a white tracer, there is more than one brown/with white tracer so make shure you have the right one.
Good luck, I spent several hours chasing this problem to find one bad wire.
2002 F350 Lariat crewcab 7.3 SRW 4x4 with 4" lift, stainless 4" turbo back Magnaflow Exhaust, DP Tuner, stock /high Idle/40 tow/80 tow, Glowshift pilar 3 guage pod, trans/boost/egt ,285/75/16 Bridgestone Dueller Revo 2's(best tire ever made!) and over 260000 miles on it and still running strong!
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