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17.04.2004: Connecting the wires
The gauge needs the ground and the 12V power. The ground nut is right at hand (10 mm again) and the cigarette lighter fuse would donor the power.

A turbocharged car without a boost gauge is no fun. It's not that you really need it, but knowing what's really happening with your engine helps a bit, and the pressure surges when you mash the pedal sure are entertaining.

My car was among those unfortunate Saabs that came without a boost gauge (not that the standard one is very useful though), and I long wanted to fix that. Here's a detailed (maybe too detailed) description of the installation process. (And I did wash the engine a couple of days after performing this work ;)

The measurements I'm getting from a 1999 Saab 9-5 2.3t with a low pressure turbo are: the vacuum is 18-20 Hg at idle, 15 Hg while driving, up to 24 Hg when coasting. With the stock engine the boost during the moderate acceleration settled around 5 psi, the highest I've seen at WOT is 9 psi. An ECU upgrade from BSR raised these numbers to 12-13 psi in second gear and 14-15 psi in third.

 

 
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