Here are a few details. I have a 92 W250 w/360 that cranks over with good power, but will not start. Fuel pump does not run when ignition is keyed up and doesn't seem to have spark to fire igntion either. Fuel pump will operate if jumpered direct from battery with 12V, so think it is fine. Checking power at ASD relay it seems to have 12v at supply and wire straight across which should be from computer I believe. The wire supplying coil and fuel pump, and 02 shows right about 1.7 volts which is what I get at those locations. I think this should have 12 volts so what is the likely culprit for low voltage here? I have tried another relay for test purposes with the same result. Could a poor ground cause low voltage or just no voltage? Could supply wire supply some power, but not enough to activate load of fuel pump etc? Funny thing is that terminal stays above 12v. Also no check engine light on dash and no communication with computer via diagnostic port.

 

There are 4 terminals on the ASD.
1. 14 gauge red should be hot all the time. (12 volts)
2. 14 gauge dark blue/black should get power when ASD coil is activated. (this feeds ignition and fuel pump)
3. 20 gauge dark blue/yellow is the ASD coil ground thru the computer
4. 14 gauge dark blue should get 12 volts from the ignition switch when the ignition switch is activated

 

Thanks, your post made me rethink what was going on at the relay. I had blown the fusible link on the red always on power to terminal 30. The way they ran that power supply is kind of strange so had to look things over good to figure it out. Why can't they use the same colors and quit changing wiring so often....here is what my connections are on ASD relay:

Terminal 30 Two- 16 guage red wires 1 through junction and then 22ga fusible link other goes to computer.
Pin 87 green/orange 16 ga powers ignition/fuel when activated
Pin 85 light blue/yellow 20ga computer ground switch line
pin 86 light blue 14 ga power from ignition switch run