Look on page 56 in this link.
Electronic Engine Control - ???Gary's Garagemahal

You can see power for the EGR and several other sensors comes from the EEC power relay. I would find this relay and unplug it, and see if your problem goes away. If it does go away, but clicks when you unplug it, you have other problems also.

 

If you go to page 63 in the link above, it says the EEC relay is mounted in the cab, in the center behind the dash right over the hump. It says there is a picture of it on page 65 in the same link.

 

 

The EEC power relay cuts off with the keyswitch. No,it should not have power to it with the keyswitch off. The only reason you are reading power on both sides is because the computer is not grounding the one side of the solenoid. That is how it works, power is on one side anytime the keyswitch is in run, and when the computer wants to activate the solenoid, it grounds the computer side, which activates the solenoid. You are just reading a "floating" voltage when the computer is not grounding the one side.

 

 

Dave is talking about the EEC's relay, not the EEC itself... need to be clear....

 

With the keyswitch off, unplug the EEC relay first. Then go out and measure for that voltage on the EGR wiring again.

If 12v is still there, then you have a wiring problem somewhere, either there are some wires bundled together that have melted together, or someone has been doing some wiring somewhere and have messed up.

If the power is gone on the EGR circuit, plug the EEC relay back in again and see if the power returns, always with the keyswitch off. If power returns, then you know for sure it's coming from the EEC relay.

Next question; Is the EEC relay welded shut or is it being told to activate? When you plug and unplug it, if there is no click from the relay, it must be welded shut, buy a new one. If it clicks each time you plug it in and unplug it, then the EEC relay is being told to cut on when it should not be.

In this diagram on page 56, in the upper left hand corner you can see the EEC relay. Electronic Engine Control - ???Gary's Garagemahal

You can see the wires that activate the relay come from two wires leaving the page in the upper left corner coming from page 28. Here is a link to page 28 diagram. Start & Ignition - ???Gary's Garagemahal

You can see on page 28, middle right side of the diagram, the white/lightblue wire which leaves and goes to the diagram we were just at. You can see it comes from splice 257 which goes to the coil, and also comes from the ignition switch.

 

I didn't catch that, thanks.

 

 

 

Ok, I can tell you are very new to this, no problem. The EEC is the Electronic Engine Control or in other words the computer that runs the truck. The EEC relay supplies power to the devices that go to the computer AND part of the power to the computer itself. So driving around with the EEC relay unplugged means you are driving around with no computer to run the engine. The ignition module has a limp home feature, so it still runs, but as you found out, not very good.

Now in your last post you may have made a very big discovery. It sounds like your complete cab is not grounded if you are touching metal and the testlight lights. Go out under the hood and look over the firewall area below the wiper motor and on either side. Somewhere in there is a ground wire bolted to the sheetmetal of the firewall, and then bolted to the engine somewhere, usually behind a bellhousing bolt. It never fails, when the engine is pulled out and re-installed, people forget to bolt this ground back up.

If you cannot find this ground, make one. You need a decent sized wire, 10 gauge would be best. If all you have is smaller wire, you can cut two or three short pieces and twist them together on the ends to make one large wire for now and crimp the ends on it.

You large ground goes from the battery to the metal of the engine, I think on yours it bolts to the starter correct? But the engine/transmission/rearend are all mounted in rubber. So there is no way for the cab to get a ground unless a ground wire is specially run to the sheetmetal of the cab. Even the cab is mounted in rubber body mounts, so the frame is not a good ground either.

 

If you look on page 36 in this link Start & Ignition - ???Gary's Garagemahal you will see G208. That is the ground you are looking for, the other end is hooked to the firewall.