MVS Volvo Forums Contributor mecheng crushes the ball out of the park with a guide on installing a boost gauge in an S70. This will be identical to V70 and XC70 Volvos, 1998-2000 model years, and very close to 850s. Here’s my 850 headliner boost gauge install.
Remember, it’s always the pink wire.
Ok, I realize this is not rocket science but there are some tricks and advice I can share and I haven’t found a complete guide to step people through this. It is not hard, but takes a bit of patience to do the job cleanly and safely as you are taping into electrical wires and adding new vacuum line.
If you are like me, you want to know how your engine is performing and boost / vacuum is a key parameter that can help diagnose leaks, boost fade, not reaching peak boost, etc.