Hey Joe,

Well the deal is that the input signal is a very, very low level pulse, probably in the 50 millivolt range. (I'm just guessing, but it's an "educated" guess based on my work with electric guitars.) Looking at the MB FSM schematic, the unpowered signal travels over a shielded twisted pair to the "Solid State" amp. The amp then has a single line to the gauge module which is also "Solid State" circuitry. The LM1815 is designed for exactly this situation. Take a low-level noisy signal, clean it up, amplify it, and output a useable pulse signal.

As for designing another circuit, I really don't think we need to reinvent the wheel. All I'm suggesting is making a replacement board that is functionally identical to the original - maybe with slightly different parts. The thing is, we've got to figure out why these things are failing if we hope to make them work reliably.

Mine was just the electrical contacts. I guess I got lucky. Another possibility is that most of the failed units are because of electrical contacts, but I did something different than other people. Maybe I cleaned my contacts better. Maybe I used just the right amount of silicon (not silicone) grease. No way of really knowing unless I got my hands on a few other units.

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Brian

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Sometimes the only choices you have left are bad ones.
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