PHILES’ FORUM IF IT AIN’T THE BULB…

BY: VIC LUCARIELLO

Hello Bimmerphiles! Happy Holidays to you as Philes’ Forum completes 32 years of publication in the Bulletin. The introductory column appeared in the January, 1987 issue. This time out I have a cost-saving procedure for you frugal E36 (92-99 3-series) owners.

When replacing the cabin filter in an E36 Bimmer, first the glovebox must be removed, and the first step in glovebox removal is to remove and unplug the glovebox lamp. When going after the cabin filter on our 1995 325is, I noticed that the lamp was not working, so I thought I would address this at the same time.

Removing the glovebox lamp is easy. Pry out the lamp from the glovebox roof with a small screwdriver inserted into the forward end of the lamp. Even a simple bulb change requires removal of the lamp assembly.

While most reasonable folks would try replacing the bulb as their first diagnostic/repair step, being that I had to remove the bulb to replace it, and being that most reasonable folks (except Vic Jr.) describe me charitably as not-reasonable, I tested the removed bulb. This can be done with an inexpensive multimeter, such as the Harbor Freight multimeter shown in Photo #1. An incandescent bulb such as shown should test at a low resistance with the multimeter set on the low-ohms scale. As you might expect, a bad bulb usually tests as an open circuit (very high or infinite resistance). In this case, the bulb tested good, and applying 12 volts across it as a double-check caused it to illuminate.

Okay, if it ain’t the bulb, what is the problem? The E36 glovebox lamp circuit is one of the simplest in all of automotivedom. Believe it or not, no expensive “smart” modules are involved on non-convertibles. Fused power (Fuse #44 on non-convertibles) from the Accessory Bus is supplied to the lamp on one wire, while the second wire provides a ground. A switch in the lamp assembly controls when the bulb is on or off. They don’t make ‘em like this anymore.

After determining that the bulb was good, my next step was to put the ignition switch in Position 1 (Accessory) and connect a test lamp across the power and ground contacts in the still-connected glovebox lamp (see Photo #2). The test lamp illuminated, proving both the power supply and ground legs of the circuit with one simple test. Electric Troubleshooting 101 tells us that any electric circuit needs both power and ground (i.e., a complete circuit) in order to work. ET-101 also insists that a test lamp be checked by placing it across a known-good 12-v source prior to doing any testing. Trust me: This is very important. Anyone who has wasted time testing only to find out the test lamp is NFG will testify to this. Note that most incandescent bulb test lamps are not polarity sensitive in that they will illuminate regardless of whether their probe or “ground” wire is connected to the hot leg of the circuit. Note also that if this test had not resulted in an illuminated test lamp, my next stop would be the fuse. Now things were getting interesting and worth writing about! Power and ground to the lamp were good and the bulb was good. WTF?? The problem had to be within the lamp assembly.

At this point most reasonable folks would simply call their BMW dealer and order a new glovebox lamp (are you seeing a pattern here?). It is part number 63-31-8-360-027, and costs about $12, but will very likely need to be ordered. The same lamp is listed for virtually every E36, but the lamp is unique to E36s.  The original part number has been superseded, and based on the following I am guessing that the present part has better switch contacts than the original. By the way, should you need a new bulb for the lamp, it is part number 63-21-7-100-805.

Frugal cheapskate that I am, I traced the circuit within the lamp and determined that its internal switch was not completing the bulb circuit when the switch sensed that the glovebox door was open. Closer examination of the switch under magnification did not suggest any broken parts, and manipulating the switch’s sensing lever revealed that the switch contacts were opening and closing as designed. Again: WTF??

I cut some 400-grit color sanding paper into thin strips. I was able to sneak the paper between the switch contacts as shown in Photo #3. In the photo, the arrow points to the 400-grit paper. A few swipes with the paper, reversing it to get at both contact surfaces, and I was ready to find out if all this effort was fruitful. I put the ignition key into Position 1 (Accessory), plugged the lamp back into its cable and vedi!, the bulb illuminated! Moreover, manipulating the switch lever caused the bulb to go on and off as it was supposed to. I concluded that the switch contacts had gotten dirty over the past 25 years, despite not having been operated very many times. So I reinstalled the lamp and patted myself on the back for saving, ahh, $12. But I wish that replacing that dang cabin filter had been this easy!

That’s all for now, bimmerphiles. See you next time.

Anyone wishing to contribute to Philes’ Forum can contact me at vic.sr@njbmwcca.org.  I’m interested in comments, tech tips, repair /maintenance questions, repair horror stories, emissions-inspection sagas, product evaluations, etc.

© 2019; V.M. Lucariello, P.E.

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