What's a safe boost level for a 1987 turbo coupe?

I read somewhere that 9 psi is stock. that's where it was with the stock bcs. I have 3.73 rear because that is what the rear tag says plus it was auto trans converted to 5-speed. It has a K&N filter in the stock air filter housing but I drilled three 5/8 inch holes in it so when i drive, cooler air can get in there. It's ghetto but i'm sure it helps. Since the metal filter housing and intercooler is black and metal it absorbs a lot of heat, I put heat reflective tape aroud them. I noticed that it doesn't get near as hot as it used to. I really don't like the way the intercooler sits right above the turbo. i might put heat wrap on the E6 manifold.

What??

What switch are you refering? I have the 87' turbo coupe engine in a 89' lx body. The stock BCS had a spring, electrical connector, and two hoses.

ohh, well my car don't have that switch, just a overboost light. I guess i just have to adjust the timing with the distributor like my 5.0 and adjust the boost with the gillis valve.