Seat belt light stays on when belt is buckled

[wil440]

Sorry to hyjack, I'm tryiing to sort out seatbelt light not going out on 98.5 my drivers seatbelt plug has 4 wires, orange and black, black/light green, blue/white, and green/red

I've got continuity on the orange and black/light green, 7.5 to 8volts on or/bl, passenger side has the 2 wires and readings are the same, I'm now going to swap the control module, anyone know what the other two wires are on drivers side, seat has no heat and no power

[wish4hemi]

I know this is an older thread, but I've been doing some probing on this 98.5/99 seat belt function, specifically the buckle sensing switch which is actually part of the retractor. It seems to be a very strange little circuit and the switch that helps drive the light in the dash is not a simple on/off of the bulb. There seems to be some logic involved.

 

My truck ('99) also has a three-wire plug going to the driver's seat. I've never found this plug to be shown in either of my 98 or 99 manuals, so the operation has always confused me. My three-wire plug going from the SCTM to the driver's front seat retractor has these wires:

Orange, black tracer = power to the latch solenoid (it is locked when the power is off)

Black, green tracer    = ground to the latch solenoid

Green, red tracer       = this is the sense wire that tells the cluster if the belt is buckled or not (actually if it's retracted or not)

 

The green/red wire is the strange one. On the cluster side of this wire (going from the cluster to the retractor), it shows 5v when the key is on. On the retractor side of this wire (going from the retractor to the cluster), it measures as an open circuit to ground when pulled out (belt buckled) and a 150-ohm resistance to ground when retracted (belt unbuckled). Also, that 150-ohm resistance is only present when the key is on and the latch solenoid is unlocked. If the key is off, the 150-ohm resistance goes to an open circuit.

 

Basically, the cluster seems to send a 5v signal to the retractor which then shorts it to ground through a 150-ohm resistance when the belt is unbuckled. It's almost like the retractor is being used as a pull-down resistor, although that's a pretty low resistance for a pull-down application. I was going to connect the green/red wire straight to ground, but it looks like it would be a dead short of the 5v signal from the cluster. If my probing is correct, it seems very strange and matches absolutely none of the factory service manual literature.

[Sycostang67]

When my seat belt light wouldn't go off I simply assumed it was the wires in the buckle side that had shorted out or broken.  The light would shut off if I leaned forward and come back on when sitting straight up.  I went to the salvage yard and got another one and that fixed the problem for several years.  The issue has returned though, those wires can only get bent around so much before they break.  If the plastic sheath supporting the belt hadn't fallen apart I doubt it would be an issue.  I'm due for another salvage yard shopping spree anyhow.  

[Max Tune]

I love walking around junk yards.

I should make a list from my three vehicles and go spend a couple hours exploring. Never know what treasures you may discover. I went once for something for my suburban and came home with the rear cup holder unit that sits under the center seat section. Has never been used, but I like the fact it's there. Plus it was only $5.

[Great work!]

Has anybody tried putting a newer all mechanical retractor in a 99.

 

Mine stops working after a half hour or so and locks. Then the light comes on. It's very uncomfortable and I have to unbuckle.

 

Let us know what you find.

[Mopar1973Man]

I've heard of guys just upgrading to the late 2nd Gens to get the non electronic seats which is easier. It was only 98.5 and 99 that had issues with this module and lock solenoids on the seat belts.

[wish4hemi]

22 hours ago, Great work! said:

Has anybody tried putting a newer all mechanical retractor in a 99.

 

Mine stops working after a half hour or so and locks. Then the light comes on. It's very uncomfortable and I have to unbuckle.

 

Let us know what you find.

If it stops working after a half hour, then I think that means the SCTM doesn’t have power. If it unlocks when you get in the truck, then the door switch portion is working. Just not the ignition feed portion. The light comes on because the lock solenoid engages. I’ve not heard of that particular situation before. 
 

Out of curiosity, does your driver’s side seat have three wires going to it (no dark blue/white) or four (with dark blue/white)? There are 3 setups as far as I can tell (from earliest to latest): one where the retractor feeds a power signal to the dash, one where the retractor feeds a ground signal, and then the later one (post 98.5/99) where the buckle feeds a ground signal. 

[Great work!]

@wish4hemi I just spent 2 hours trying to figure out this stupid light. Every time I thought I had it would do something different.  My driver seat has 4 wires, none on the buckle.  Two wires has the retractor solenoid that's 60 ohms. The other 2 are shorted when belt is retracted and open when pulled out. One of those wires is blue with white I found it on an old diagram before the seat belt was in the chair it was in the roof area the diagram showed it grounded by the rear speaker. But mine isn't grounded in fact doesn't seem to do anything  my seatbelts light goes out after a few seconds regardless. Maybe the truck has to be moving. Disconnecting the module or seat wiring will turn on the light .

[wish4hemi]

@Great work! Fuse 16 in the junction block is the main thing that keeps the solenoid unlatched after the doors have closed and the 30-minute timer has expired. Since you have four wires to the driver's seat, your truck matches the service manual. "The driver seat belt switch is normally closed, providing a battery voltage signal to the instrument cluster when the ignition switch is in the On or Start positions." Section 8U-2. However, I do not believe this to be a problem with the seat belt switch in the retractor.

 

It sounds to me like the SCTM is not getting the F13 18DB RUN-ACC feed from Fuse 16 in the junction block. Or maybe the power is being supplied but the SCTM is damaged internally and not taking that power signal correctly. Section 8W-67-2

 

An easy way to test this is to turn the truck off, leave the windows down, and walk away for 30 minutes. When you come back, leave the doors closed and reach in the window to tug on the driver's side belt. It should be locked. With the doors still closed, reach in the window and turn the ignition on. If that unlocks the belt, then Fuse 16 and the associated F13 circuit are working properly and the issue is elsewhere. If the belt is still locked with the doors having never been opened and the key is on, then the SCTM is not getting a RUN-ACC voltage.

[Great work!]

Thank you I'll try that. I made a custom sub woofer that goes where the lower center seat goes but kept the armrest  and frame. I just shoved that module under there and maybe it moves around too much even with the radio off. So it thinks something is wrong with the motion sensor. 

[Great work!]

Update. I think I found the problem. The blue wire from the run/acc fuse looked like the pin was not making good contact I noticed it was a bit lower in the socket than the other pins. I extracted the pin and the metal was cracked so it wasn't as springy. I stretched it back out and it works like described above. I'll see if I can find a new pin or connector on a junker. I relocated the module from next to the sub woofer to under the seat and screwed it down I also cleaned up the sensor ball and switch inside. The mysterious blue/white wire I still don't know where it goes I even removed the back seat and lifted the carpet. I gave up trying to track it down. This has been a difficult problem to find. I'll take it for a long drive soon to see if it that was indeed the issue.