Make up a fitting to accept the threaded switch and a hose barb or something similar, connect to the regulated side of your air compressor, slowly dial up the pressure and check continuity from the switch to the fitting.

That's a good idea. Are there any quality aftermarket over boost switches that are adjustable for boost level? Most of our switches are going on 30 years old...

Hobbs makes adjustable pressure switches, but they are 1/8NPT not M10x1.0mm -- similar enough to thread in, different enough to damage threads of the housing.

I did a search a while back and found a switch that would thread in, wasn't adjustable, but was available in different pressures. I don't have the info handy but I found them with about 20 minutes of the google.

I am hooking up my HKS unit and snapped this picture as it shows another reason why I prefer a high quality unit. Simply, the mode of failure.

https://c1.staticflickr.com/4/3820/3...0f43074f_c.jpgIMG_4012.jpg by Shannon, on Flickr

The HKS unit uses a separate boost sensor, if a overboost is detected it will warn and/or drop the boost down to separate pre-set. I believe also that the higher quality solenoids fail 'open' as a matter of principle.

Correct -- some still use a valve designed to work in the reverse, where it defaults to closed and, in this case, raises the boost. Bad design in regards to failsafe.

Biggest risk is a 20 cent vacuum hose. That was an expensive lesson.

True. The original fabric covered rubber vacuum lines eventually get brittle and crack easily if moved. The fabric covers the cracks that become vacuum leaks and you can't see the damage.

mine was the angled one on the boost conrtoller valve. It split at the track that was why i got that set of pistons and cyliders from you.

I have the Grimmspeed MBC too.

Call me an idiot or wuss, but I actually turn it down to minimum at the track (.3bar) until I can reasonably drive the car 'fast' at that level. So far it's been plenty fast for me.

I turn it up on the street for occasional fun moments.