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4WD dash light/

Discussion in 'Ram Trucks' started by vmj, Dec 18, 2013.

  1. vmj

    vmj Senior Member
    from conn
    Messages: 752

    2000 3500 ram 4wd light wasn't coming on in 4x then it was flickering when it was in 2x would stay lit for awhile in 2x ??????
     
  2. NicholasMWhite

    NicholasMWhite Senior Member
    Messages: 175

    On the front axle there is what's called a Central Axle Disconnect (or CAD) it is a vacuum operated collar that locks in the front axle. The light will not come on until the collar has fully engaged, if the light is not on your front axle isn't locked in and you don't have 4x4. The possible problems are bad vacuum motor, rusted or broken vacuum lines, or faulty vacuum switch in the transfer case. You'll have to get under the truck with a vacuum pump and or vacuum gauge to determine which is the problem. I had a similar problem a while back with a 1997 2500 and it turned out to be the vacuum motor, which is the hardest of the problems to fix. I would assume there are youtube video's showing how to do it if you were interested in tackling it yourself.
     
  3. vmj

    vmj Senior Member
    from conn
    Messages: 752

    if it was a vacuum issue then whould it not go in and out of 4wd? it is going in and out.. Thanks
     
  4. SnowGuy73

    SnowGuy73 PlowSite Fanatic
    Messages: 24,867

    Probably an issue with the computer, I wouldn't worry about it. If it bothers you put s piece of electrical tape over it.
     
  5. quigleysiding

    quigleysiding PlowSite.com Addict
    Messages: 1,098

    The switch is on the front axle. Check the plug.
     
  6. NicholasMWhite

    NicholasMWhite Senior Member
    Messages: 175

    It is going in and out precisely because it is a vacuum issue. Unlike an electrical component that either has 12 volts or none (in most cases) vacuum varies between 0 and 20 inches of vacuum depending on engine load and rpm. During high vacuum periods it could over come a leak (in either the lines or the vacuum motor diaphragm), half open switch, or a sticking vacuum motor. Vacuum is required to both engage and disengage the axle just on opposite sides of the vacuum motor so it could jump in and out regardless of shifter location.
     
  7. NicholasMWhite

    NicholasMWhite Senior Member
    Messages: 175

    I hope this is a joke. Nothing in the system is computer controlled and if the 4wd light is not on then the front axle is not engaged and you don't have 4x4.
     
  8. SnowGuy73

    SnowGuy73 PlowSite Fanatic
    Messages: 24,867

    So you're saying when his light was flickering the four wheel drive was going in and out with every flash of the dash light....... Ok!
     
  9. vmj

    vmj Senior Member
    from conn
    Messages: 752

    I hope not!!!!
     
  10. vmj

    vmj Senior Member
    from conn
    Messages: 752

    had no light at all.. tested plug end with jumper.. 4x light lit,so I put in new switch... still no 4x light!
     
  11. NicholasMWhite

    NicholasMWhite Senior Member
    Messages: 175

    You need to check the vacuum system out. There is a switch in the tcase, a motor opposite the switch you replaced, and rubber/metal lines between the two.
     
  12. quigleysiding

    quigleysiding PlowSite.com Addict
    Messages: 1,098

    Which switch did you change ?
     
  13. vmj

    vmj Senior Member
    from conn
    Messages: 752

    switch on front axel
     
  14. rjigto4oje

    rjigto4oje PlowSite.com Addict
    Messages: 1,294

    Try to make sure the linkage is adjusted as they get a little older it may have come out of aadjustment
     
  15. vmj

    vmj Senior Member
    from conn
    Messages: 752

    I will look at that
     
  16. NicholasMWhite

    NicholasMWhite Senior Member
    Messages: 175

    I am going to break this down as far as I can, as I feel like a broken record.

    Your problem lies in one of three places:

    Vacuum Motor (see attached picture): this is located on the axle, opposite the indicator switch you recently replaced

    Control switch (see attached picture): this is located on the transfer case. When the little silver ball is depressed by the pawl inside the transfer case it reverses the flow of vacuum to the opposite side of the vacuum motor and slides the collar to engage the front axle.

    Vacuum lines: This seems self explanatory. They could be leaking from the engine to the control switch (including the check valve) or on either line from the control switch to the vacuum motor.

    You need to get under the truck and do some testing with a vacuum pump or at least a vacuum gauge now. Your other option is to just keep throwing parts at it until something sticks but I assure you that your problem lies in one of those 3 places. I have quite a bit of experience fixing the 4x4 actuation on these trucks and have an extremely good grasp of how they operate.

    CAD vacuum diagram.jpg

    control switch.jpg

    vacuum motor.JPG

    diagram.jpg
     
    Last edited: Dec 29, 2013
  17. quigleysiding

    quigleysiding PlowSite.com Addict
    Messages: 1,098

    Is the truck going into 4x4. have you checked the vacum lines going to the actuator.
     
    Last edited: Dec 29, 2013
  18. vmj

    vmj Senior Member
    from conn
    Messages: 752

    Thank you... That was all replaced two years ago.... Probably that again! I just droped off truck at a friends garage to have him look at it tomorrow!!
     
  19. vinnys

    vinnys Senior Member
    Messages: 112

    You forgot the most important part. CHECK THE COMPUTER!! LOL