"Bulb Out" indicator on dash issue
 

Hey guys. I'm trying to track down a gremlin in my '88 260E eclectrical(!) system that is related to a bulb that is located at the bottom of the passenger side rear door panel. I've had the car for over a year and it is driven by my son most of the time so it's not something I see - the glaring dummy light indicating a malfunctioning bulb on a daily basis. Yesterday being the beautiful Feb day it was here in Ohio, I thought I'd dig deeper into it.

I was elated at first that I had finally FOUND the bad bulb when I discovered the courtesy light was 'out' but further digging proved not so easy as a blown bulb filament! Bought new bulbs but should have simply saved myself time by placing a known-working bulb into the fixture. My next move was to check voltage at the wires and I discovered there is roughly 12v at EACH one of the two plugs! This seems strange, in that, if the two wires are shorting against each other somewhere in the harness, I figure that would cause a blown fuse someplace and there wouldn't be ANY voltage at the device (light).

I pulled the black insulation plastic off the two-wire combo (one was red/orange and the other brown/?) and noticed some damp-ness actually to the point of a drip or two. Dried it all the way into the rubber bellows tube at the door jamb near hinges. Still can't figure out the 12v coming through each of the leads?! Any thoughts?

Dale

Your exit lamp is not the source of your bulb out indicator coming on. Those bulbs are not monitored.
The reason you have 12 volts on both sides of the non-functioning exit lamp is that it is not getting a ground through the door switch. It could be the switch itself or a broken wire going to it. The wires sometimes break from flexing when the door opens, however the rear doors don't get as much use as the fronts. If you have moisture getting in, there might be corrosion in the switch.
Try grounding the brown/gray wire to see if your exit light comes on.

Check your license plate lamps. I missed those once on my car.

The bulb monitoring unit is only for external lamps.

Both are excellent suggestions, I will take a look at the tag light again, thought I had checked them before but I didn't yesterday. I'll report again...

Dale

Nope. Both license plate bulbs working fine. Another idea?

Dale

Have any of the exterior bulbs been changed to LED?

No, completely stock bulbs. I have made sure there is no corrosion in the sockets on all the rear bulbs but haven't looked at the front yet. It's possible the indicator is faulty I suppose...

Dale


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I see that you also have a 1995 E320. That car has the same lamp monitor controller, 126 542 01 32. You could try it in the 260E to eliminate it as the problem. It just unplugs from the fuse and relay center under the hood. It is a 5 1/2 by 1 1/4 inch black plastic module.

Good idea. I'll try to do that in the next couple days and will report back. Thanks again :-)

Dale

EDIT: Any guidance on removing that sucka!? Tried to lift straight up on it however there's little to no clearance for the aft 1/3 of the module so it would only lift at the forward half. There were what appeared to be some wiring harness(s) still attached that were IMPOSSIBLE to get to! Help me Rhonda!

The module plugs into 3 sockets. One has 8 connections, one 10 and the center one 16 so it will be quite tight. I'll pull one out in the morning and give you tips.

Ok, sounds great! Thx

Dale


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Pulled my module out.
Remove the module next to it to get better clearance. It has only 13 pins so comes out fairly easily. Rock the lamp monitor module back and forth to evenly pull it out of the sockets. On mine the 8 and 10 pin connectors came out of the connector holder and stayed on the module. Not sure if they were suppose to do that or stay in the holder. Pressed them off with a small screwdriver.
If you have one of those tools with the hook to pull the instrument cluster, it looks like the job would be easier as there are spots where you could get it under the module to help rock and pull it out. You could improvise with a piece of coat hanger wire but it is doable without, just hard on the fingers.

Edit: Helps to get at the relay center if the hood is put in the vertical service position.

"Bulb Out" indicator on dash issue
 

Thank you for doing that! I had tried to pull it out yesterday as I had a few minutes but I encountered pretty much everything you've mentioned here! I was thinking that the other module needed to come out before but I was having trouble getting it to budge. Well, all I can do is work with it until it comes loose and I'll report back.

Dale


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Check for any discoloration of all the tail lamps.......

The side marker in he rear light clusters tend to go out or get loose. That will trigger the instrument cluster indicator.

When does the lamp come on? If it comes on with the running lamp position (first position clockwise) it is in your running lamps, second position it is a headlamp issue, both of these will reset and turn off the light if you turn off the switch.

If a turnsignal or brake it will come on when the light is actuated and only reset with the key. Backup light will only come on in reverse.

I am pretty sure I have checked the bulbs for discoloration and have checked the marker lights as well. Can't hurt to look again! Thanks for the suggestions.

Dale