I like what you are doing. The circuit board is probably trashed, I would be looking at the incoming power and following the silver trail to see how it gets to the battery. But grabbing a better board at the P&P would be much easier? Just hope that the module doesn't need updating, which I doubt.

Because the case is water proof, mounting in the engine bay shouldn't be a problem. The newer cars have the module in the engine bay, I guess Volvo got tired of the complaints from dealers trying to replace the module and taking so long to do so. Let us know how it turns out...

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Keeping it running is better than buying new