CDL Relay failed only one test

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May 11, 2010
CDL does not engage when I go to low. 30 amp fuse is good. I installed CDL switch in dash, still no work. I pulled relay and tested it. It passed every single test except continuity between pins 6 and 7. No continuity either direction. This bothers me because it seems like there should be more than one item fail on the test series. With 9 volts applied, I hear the coils snapping the switches in and I get continuity everywhere I should. Any thoughts out there?
4L switch, Indicator Switch, Actuator motor?

Has it every worked or is this a new to you rig? Sometimes they take quite a bit of exercising (on/off). Even with mine working I didnt use it for awhile and had to "un-stick-it". I try and make a point now to hit the button every now and again between wheeling.
When testing the relay, were you putting the positive lead to Pin 6 and the negative lead to Pin 7? If so, you won't have continuity because there is a diode (electrical one-way valve) in that circuit. Try reversing your ohmeter leads and you should have continuity.
Nothing Happens

The rig is new to me but i know its history and neither of the previous owners ever went off road or would have checked the CDL. There is no whirring noise and I have driven in low range and know that the center is not locked by free turns. I check pin 6 and 7 in both directions and there is no contibuity either way. Does someone know how this problem alone affects the system? Can 6 & 7 kill the system? I have all other continuity on the relay and am trying to decide if I should condemn the switch and replace it or keep testing.
Pin 6 Not Connected to anything!

I think my CDL relay is fine. It passed all tests except pin 6 to 7 continuity. I don't have a manual and have been researching posts. The test sequence I found here must be for a different model. I found a manual page showing a diagram for my 96 and pins 6 and 8 are not connected to anything inside the relay.

So is it my actuator? From what I have read, the CDL indicator switch failure will only affect indicator lights and the front and rear lockers engaging.


  • Center Differential Lock.pdf
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If the relay isn't clicking when the CDL switch is pushed and/or low shifted, it is most often a bad contact/connection at the limit switch in the actuator. The limit stitch supplies the ground to activate the relay, so no ground, no relay click.

I posted some thoughts on trouble shooting on page 3 of this thread.

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