Major Electrical gremlin
Logistics Pro
Joined: Aug 2009
Posts: 3,609
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From: Arizona
Here is a diagram of the connector on the fuse box, and another of the wiring diagram. The overview shows different pin numbers on the IDM relay than the first one. All of this is directly from the 2002 Ford publication.
Lets not rule out the possibility that the PCM is responsible for providing the ground reference to the relay or the IDM, I do not know the answer to that. Seems you could figure it out by measuring values at all terminals to see what is missing. Also did you note the diode that is in the PCM ground path?
Wish I was there to help but it sounds like you know quite a bit about electrical, probably more than I do. I need to bone up on wiring diagram reading, has always been one of my weak points. Maybe Rich can offer some insight on the diagrams, I think he is pretty sharp in that area.
Hope this helps
Lets not rule out the possibility that the PCM is responsible for providing the ground reference to the relay or the IDM, I do not know the answer to that. Seems you could figure it out by measuring values at all terminals to see what is missing. Also did you note the diode that is in the PCM ground path?
Wish I was there to help but it sounds like you know quite a bit about electrical, probably more than I do. I need to bone up on wiring diagram reading, has always been one of my weak points. Maybe Rich can offer some insight on the diagrams, I think he is pretty sharp in that area.
Hope this helps
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Elder User
Joined: Aug 2015
Posts: 535
Likes: 3
I know nothing on wiring. Just testing and eliminating. Way back I posted that I tested the pcm plug for grounds and power. All them listed. They all worked perfectly. Now that I have idm signal out of it, I now know the pcm is doing its job. The problem is the signal does not reach the relay, and its wh blk wire changes colour to I don't know as it passes threw the fire wall. So the fuse box is a mystery to me. It has 3 or 4 of those plugs on it, and none of the colours match.This happened before to me and some one on another site found the correct colour coding for my fuse box. I wanted to do the mod for the fog lamps that makes them stay on when you hit high beam, giving you lots of light. It required cutting a green/black wire on the fuse box and grounding it. All the drawings said a pink wire or something so I couldn't find it either. Guy saved me with a correct colour for my box. Didn't give me a drawing though. Darn it. So I'm trying to find that guy or a drawing or both. No luck so far. It was way back.
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Elder User
Joined: Aug 2015
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Thank you. The relay I pulled is conventionally numbered. 30 for hot all the time, 85 signal in 86 ground,87a out to idm, 87 not used. So, 30 is hot at relay. 85 is dead, signal doesn't make it. 86 is also dead, not grounded, open. 87a obviously is dead because it doesn't trip. Im going to test that relay hole on the fuse box to the idm plug power pin, 14 I think, after dinner. If its live then the only wires I need to trace are the signal and ground. I'm thinking my fuse box it messed up inside. It seems odd that all the terminals are dead, except the main power for it. Will post my results. 85 and 86 are going to be tough not knowing what colour they are coming out of the fuse box.
Logistics Pro
Joined: Aug 2009
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From: Arizona
The connectors on the fuse box are all shaped differently and have different pin counts. If you locate the one in my diagram you can check pin number 4 for the signal.
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Elder User
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I understand everyones frustration. but there are three of those plugs on my box and they all look the same. Will dig deeper to determine which one has pin 4. they are c270f g and h. all the same. Whats needed in this case is a drawing of that fuse box from the back, showing which of those 3 plugs goes were. Since my colours are different than the drawing I can't determine which plug goes were. If I knew c270g went in a certain spot, the I can figure out the colour code. But the drawings only show the relay side and the corresponding plug, not were it comes out on the back. I'm going to have to count wires, and order of wires, and wire sizes to decipher the colour code and plug position.
Logistics Pro
Joined: Aug 2009
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From: Arizona
Thomas, am I correct in assuming that when the PCM power relay closes it energizes the IDM power relay on terminal 86? (along with the fuel pump relay?) And if this is the case then pin 80 on the PCM would provide ground to both the IDM relay and the FP relay?
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Logistics Pro
Joined: Aug 2009
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From: Arizona
That is why I am thinking pin 80 supplies the ground to the relay when commanded. But you said you got a + signal from pin 80?
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Elder User
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Now that's a helpful clue. I'll get the wife to hold the horn while I unplug. Thank you. I will post results after dinner when I do that. I'm hoping its the fuse box. I understand ford has had issues with these boxes burning up. OMG!!! It just came to me. I've been getting intermittent transformer type smell in the cab about once a month. I'll bet my fuse box is welded together inside! These tests will confirm. I'll let you know.
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Elder User
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yes pin 80 was about 10/11 volts to the relay. But never made it . lol The pcm drawing clearly states it injector relay power control. Usually that means positive. If I'm wrong, then of course, my pcm has a real issue. both of them.