924Board.org

[John Brown]

I wanted a positive indication if the overboost protection activiated. To really bring it to the drivers attention and to help differentiate from all the other kinds of things that make motors suddenly stop.

Radio Shack: 10mm red LED rated at 40ma, 270 ohm resister (any wattage, but small, non-critical).

The 270 ohm R goes to the brown/white wire from terminal 31 on the fuel pump relay. Other end of R to positive lead of LED. Neg LED goes to ground.

What this does is put the LED in parallel with the cutout switch in the intake duct. When the safety switch is (normally) closed the terminal 31 of the fuel pump relay is at ground (zero volts). The voltage to the LED is zero and it stays off. When the safety switch opens the voltage at terminal 31 rises to 12 (system) voltage because there is no longer any voltage drop across the relay. The LED now has 12 volts applied and so it turns on. (The current through the LED is not large enough to allow the relay solenoid to pull in; the LED comes on but for all practical purposes the relay thinks it has lost it's ground and so stays off)

This is NOT an independent indication so it is not redundant. All it really says is that there is voltage to the relay (key is on) but that the ground is open (safety switch open, or broken or something loose).

[924martinirossi]

John sounds good to me. I'll have to do the mod and hook up a guage and test.

Michael

[kyhm]

FWIW, I have a replacement designed for the Fuel Pump relay, which would include an LED and audible alarm for the overboost, and an override switch (for living dangerously). It would also pre-pressurize the fuel system at key-on, and use a common 30A relay, eliminating the need for the expensive Porsche ones as replacements... This was a year ago I started on it, is anyone interested in such a beast?

[John Brown]

Sure.