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1990 k2500 no 4wd

Discussion in 'Chevy Trucks' started by geta4x4, Feb 6, 2006.

  1. geta4x4

    geta4x4 Junior Member
    Messages: 4

    First need for 4wd this year and it won't engage. When I put in 4 wheel high or 4 wheel low nothing happens, no light and no front drive. I searched other posts to get an idea of the problem and this is what I have done to troubleshoot so far.

    I checked the front drive shaft and it is turning while driving.
    With the front wheels off the ground (key on and in 4 wheel high) I can turn both front wheels.
    Checked voltage at thermal actuator and there is no power.
    Brown wire under carpet that goes through the floor at shifter is +12v.

    What part on transfer case sends the power to the thermal actuator?

    If I put on a manual actuator with other part not working will I cause damage?
    Thanks for any help.
  2. TLS

    TLS PlowSite.com Addict
    Messages: 1,425

    It's likely just your thermal actuator.

    You can buy a new one (they are slightly improved since the '90 era ones), or you can buy a manual one.

    Your shifter mechanically locks the T-case.

    With truck in PARK, and T-Case lever pulled back to 4x4, you are unable to spin the front driveshaft by hand, correct? If you can spin it, your T-case is the problem.
  3. Jerryjks

    Jerryjks Junior Member
    Messages: 14

    Did you check the fuse ?
  4. geta4x4

    geta4x4 Junior Member
    Messages: 4

    With truck in park and in 4 wheel high I can not turn front drive shaft. The two fron half shafts turn freely with front wheels off the ground. I have no power to the actuator. Fuse is ok. If I put in a manual actuator on and the switch or relay in transfer case is bad will this damage the transfer case?
  5. lorentzlawnsnow

    lorentzlawnsnow Senior Member
    Messages: 143

    it won't damage your t-case the only thing that will be different is the light showing the front wheels are engaged won't come on.
  6. stritzy

    stritzy Junior Member
    Messages: 2

    I would test the two wire switch on the top of the transfercase by jumpering the two wires together then check for power on wires to front actuator. I had that switch go bad on my truck this year
  7. geta4x4

    geta4x4 Junior Member
    Messages: 4

    Thanks for all the help. I hard wired in a switch to the thermal actuator and 4wd now works. The 4wd light also works there must be a switch in the front differential to control the light. I will wait for better weather to find out where the original problem was, probably tcase switch, relay, or wiring. :waving: