Help with 97 80 Series: CDL / ABS Lights do NOT come on with CDL Sensor Jumped, but Relay Clicks and CDL Locks (1 Viewer)

[Charles4x4]

Hi all, I've read 7-8 Mud threads and the George4wd thread and still can't solve this one. I recently swapped in factory locked F/R axles (mine were non-factory locking) and wanted to test out the lockers. When I put it in low, I noticed that the CDL light didn't come on (so I couldn't test the new F/R lockers). I had a CDL switch, so I installed it and did the Pin 7 Mod. I then drove it and could immediately tell the CDL is working.

To make certain, I turned the truck off, turned key to on, and pressed the CDL switch and I CAN hear both the relay in the drivers kick panel area AND the CDL actuator energize.

Next, from my research, the CDL Sensor is usually the problem if it isn't engaged much (this one likely wasn't put in Low Range in 20-years). So, I found the CDL Sensor at the front passenger side of the T-Case, unplugged it, and jumped it with a paper clip. Unfortunately I still get NO CDL or ABS LIGHT. I know the ABS bulb works (it comes on when I first turn on the truck) so it likely isn't the bulbs.

From what I read, most of the time the jump works which means that it's the switch that is the issue (due to not energizing often enough). But no luck on mine.

From what I've read, since I've done the Pin 7 Mod, the L4 switch wouldn't affect this anymore. But, just to make certain, I then found what I think is the L4 switch (same plug type, just opposite side of the T-Case) at the rear passenger side of the T-Case and tried jumping it. No change either...as expected.

From another thread:
"...put a wire link to bridge the CDL switch/sensor connector. That 'should' cause the dash CDL light (and ABS light) to come on. If it doesn't then you have a wiring/harness issue from that connector back to the dash/diff lock ecu..."

I checked the 30Amp Diff fuse in the drivers knee level fuse area and it was fine. I swapped it anyway just in case. I wouldn't think that it would be the CDL Actuator since the CDL is actually working, but could be wrong.

Any ideas on where to look next?

 

[ppc]

@Charles4x4 , The CDL locking which is the 4low, dash switch, CDL relay are completely divorced from the sensor that controls the dash light. Based upon your description the everything is working correctly except for the dash lights. Are you certain you properly shorted the pins on the wiring harness versus shorting the connector on the sensor. As long as you have the vehicle turned on the dash lights should both illuminate irregardless of anything inside the transfer case. It is purely a wiring issue from that front connector harness to the speedo cluster.

 

[bubfuji]

I recently helped a buddy with the same issue. Press in the CDL, I could hear the CDL actuator engage. No DIFF light or ABS light. I jumped the CDL ball switch at the front of the T-case. Still no dash lights. The harness that has the 7 pin mod plugs into the Transmission control relay. Also called the 4x4 control relay. The wiring diagram calls it the center diff control relay. There are three relays inside Transmission control relay.

To engage the center diff
1. Shift transfer case to low (Relay action completes a circuit)
2. Press the center diff lock button. The CDL actuator will lock the center diff.
3. The CDL actuator will close a ball switch that tells turns on the DIFF light and ABS light.

I replaced the CDL ball switch (which was bad) and the 4x4 relay module one of the relays was inside was bad.

In your case the CDL light switch, (front of the T-case) and or the transmission control relay is bad.

Inside of the Transmission control relay (4x4 relay, center diff relay)