I've always thought my 85 740 with Bosch ignition didn't have a test-terminal that generated diagnostic ignition codes. However, after reading the 'Knock Sensor Testing Procedure' in the link below (see last para in the Knock-Sensor section) - it seems there is a Red/Yellow wire in the driver-side area of the engine-compartment near the Air-Mass Meter that can be used to test your knock-sensor. I just tried it and it works !

http://www.brickboard.com/FAQ/700-900/EngineSensors.htm#TestingaKnockSensor

After hooking up an LED to the terminal, it lit when I turned on the ignition, and went off when I started the engine. Then - to see what happens, I disconnected the knock-sensor with the engine running. After about 10 secs, the LED flashed 3 times, after which it kept up a 4-flash sequence. I connected the knock-sensor with the engine running, and the flashes kept going. Shut off the engine, and restarted it - and the LED stayed off now (indicating no problem with the knock-sensor).

SO - does this test-point also generate other error-codes ? And does anyone have a list ? There is also another free single-terminal wire (orange or brown) near the power-steering reservoir that is similar to the knock-sensor test terminal. Anyone know what this is for ?

Thanks,

Noel