I have a 1988 240 DL. I've been trying to figure out why the fuel pumps and fuel injection isn't working. In checking the wiring to the fuel pump relay, I've discovered that the red wire to the fuel pump (terminal 30) has good voltage - 12 volts until I turn the ignition switch to the "on" position to check the wiring to and from the relay switch.
I have about 1 volt goint to the fuel pumps and to the fuel injection. I've run a wire directly from the battery to the #30 terminal on the relay, but when I turn on the ignition switch, it drops to about 1 volt.
Anyone have an ignition switch wiring diagram?

 

The red wire doesn't go to the fuel pump.The red wire(terminal 30)comes from the junction box located near the batt and goes to fuse #6 then to the main/fuel pump relay.Terminal 30 has constant voltage doesn't matter if the key is in the on or off position.I'll take a guess and say you have a bad relay,here's how to check it.


1. While cranking the engine,check for batt voltage at terminals 87/1 and 87/2.If you have voltage at both terminals,the relay is ok.If either terminal doesn't have voltage go to step 2.

2. With the ignition off,check for batt voltage on terminal 30.If you don't have voltage,check fuse #6 and the wire going to the junction box.If you have voltage go to step 3.

3. With the ignition on,check for voltage at terminal 86.If you have voltage go to step 4.If you don't have voltage,check the blue/green wire to ignition switch.

4. Disconnect the relay from the connector,while cranking the engine,check for continuity between ground and terminals 86/1 and 86/2.If there is continuity at both terminals,relay is bad.If there is no continuity at either terminal,check the wires going to the ecu,if all wires check good,your ecu may be bad.



Dan

 

Thanks. I already know all of that, but my relay is fine. I tested it with a battery and everything works exactly like it's supposed to. When the relay is fine and the computer is fine, you have to get a wiring diagram and go to work. That's what I was doing. The red wire on #30 had 12 volts until you turned the key on. It then dropped to about 1 volt as I described. I connected a wire from the battery to #30 and now it cranks and runs fine. I have no idea where the problem is with the original wiring, but somewhere it was screwed up.
Thanks for your help, everything is working great now.

 

I did the best I could with the info in your original post.

Your getting a bleed over from another circuit,that's why you have 12v until you turn on the ignition.

Now to the problem at hand.

Make sure you have good clean connections at the positive batt terminal and the junction block .
You have one wire that comes from positive batt terminal into the junction block.There are three wires coming out of the junction block.One wire goes to the headlight step relay,2nd wire goes to the key switch(30),3rd wire goes to the #6 fuse then to the ecu and the main/fuel pump relay.Start at the battery and work your way to the relay,it's a very simple circuit.



Dan

 

Great. My solution went around this junction and directly to the fuel pump / fuel injection relay. So, the car cranks and runs great, but the headlights don't work. I obviously need to adress this junction and get current to the headlight relay.
Can you tell me where this junction is located?
I see it on all my wiring diagrams, but I have no idea what it would look like or where it would be located.
Thanks, I appreciate your help, you have answered what was going to be my next post before I even asked the question.
AWESOME!!!

 

Look at the pic,Connections are under the plastic cover.



Dan

 

I'm gonna jump in here because I'm having a similar issue.

My '88 240 Wagon quit running about a week after replacing the in-tank fuel pump/sender unit. In fact, it was running better than it had ever ran since I've owned it.

Was thinking relay, cheap fix. Nope. Doing the same thing, but relay clicking intermittently and fast. Using new relay, I did some tests and discovered this...concerning the power from relay:

Ignition off:
30 - 12v
87-1 - no voltage (henceforth noted as "0")
86-1 - 12v
87-2 - 0
86-2 - 0
85 - 0

Ignition in 1st position:
30 - 12v
87-1 - 0
86-1 - 12v
87-2 - 0
86-2 - 0
85 - 0

Ignition in 2nd position:
30 - 11.73v
87-1 - 11.73v
86-2 - 2.36v
87-2 - 0
86-2 - 11.65v
85 - 11.95v

Ignition in starting position:
30 - 8.93v
87-1 - 8.99v
86-1 - 2.37v
87-2 - 8.69v
86-2 - .12v (?)
85 - 9.9v

Just assuming that it surely isn't enough power to run the fuel pumps.