I rigged my 148 box up on my desk tonight to check it (can?t do it in the car since it is not running at the moment).
I powered it with a stable 13.8v power supply, measured the voltages with my multimeter, stimulated it with my frequency/pattern generator and looked at the signals with my 20MHz oscilloscope.
All the signals are un-terminated to see any reference voltages or similar.
Results:
1: OBD diagnostic socket (in some markets: serial interface) /5v
2: Coolant temp sensor /5.5v
3: Check Engine Light output, shared with ECU pin 22. Signals: 12-off, 1-on /5.5v
4: PRE-IGNition, output to ECU pin 28. Signals: 0-Preign, 6.5-stable, 12-knock /5.5v
5: 12v supply, constant /Supplied with 13.8v
6: 12v supply, switched /Supplied with 13.8v
7: Throttle idle switch /5.1v
8: Load Signal Tq, from ECU pin 25 /5.4v
9: /Gnd
10: Engine speed sensor /5.1v
11: Engine speed sensor (shield) /5.4v
12: Knock sensor (shield) /5.1v
13: Knock sensor /6.1v
14: EGR, Ground connector on engine (power ground) /5.1v
15: EGR, converter, control /6.25v
16: Igntion amplifier drive, trigger /5.1v
17: Engine speed signal output. Signals: 6.5-cranking, >8-idle /Gnd
18: Selector wire. Signals: 5v-disabled, grounded-enabled /5.1v
19: Selector wire. Signals: 5v-disabled, grounded-enabled /5.5v
20: Ground connector on engine (signal ground) /Supplied with ground
21: /5.1v
22: EGR, temperature sensor /6.25v
23: Engine speed sensor /5.1v
24: /Gnd
25: /Gnd