Date: Fri, 24 Oct 1997 14:22:40 GMT From: FEDavisnopsamdnet.att.net (Fred E. Davis) Subject: Headlight relay problem FIXED
There were a number of discussions recently about problems with the headlight relays, and whether this was a design fault that should have been corrected. Well, folks, it just happened to me ('93 9000 CSE turbo), and, being an engineer who just happens to have the electrical system service manual with schematics, I thought I'd take a look myself. In my situation, the symptom was loss of high beams - the high beams wouldn't turn on (only low beam), the high beam indicator would never come on, and the fog lamps wouldn't switch off when selecting high beam. I could hear the headlight relay click when I selected high beam, but they didn't come on. Here's the solution: There *IS* a manufacturing flaw in the "Lamp Control" relay, aka "Filament Monitor," located in the small distribution/relay/fuse box near the battery. The headlight relay is the large, red, rectangular relay, and just to its left is the square, orange, filament monitor. My part is labeled "Lamp Control 41 09 070 5KG005675-01". Inside is a small circuit board that's soldered to the metal contacts that protrude from the bottom of the relay. The problem is that there is only a minimal amount of solder joining the circuit board to the metal pins. These solder connections are mechanically supporting the circuit board, and since solder (a lead/tin alloy) has very little mechanical strength, these joints _will_ _fail_ given enough vibration over time. The good news is that the fix is quite simple. Pop off the orange relay cover, and resolder the connections along the edge of the circuit board. I honestly believe this to be a manufacturing defect, and potentially a design defect. There should have been more solder to provide additional support. The circuit board *should* have more mechanical support which could have been easily obtained by including board supports (card edge guides) molded into the relay cover. (The high beam relay *does* include such support!)
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