Fuel pump relay wiring
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From: Minneapolis, MN
Fuel pump relay wiring
I have a problem somewhere, but have been unable to figure it out yet. The only way I can get the engine to start is to hotwire the red and yellow wire from the fuel pump relay directly to the battery. The yellow wire is getting power before the relay, but the red wire is not. I've traced the red wire to the computer, checked for continuity, and it does. I've also replaced the fp relay pigtail and relay.
From what I've read the computer powers the red wire when the key is turned on, is that correct? and I know the yellow wire is hot all the time, that's about all I know about how this works. I'm at a loss right now, not sure what to do next, can anyone shed some light on how this system works? or what else I should be looking at?
on a sidenote I just replaced the ignition module tonight. did'nt change the situation at all.
From what I've read the computer powers the red wire when the key is turned on, is that correct? and I know the yellow wire is hot all the time, that's about all I know about how this works. I'm at a loss right now, not sure what to do next, can anyone shed some light on how this system works? or what else I should be looking at?
on a sidenote I just replaced the ignition module tonight. did'nt change the situation at all.
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From: Lyman, SC
You can find the drawings here:
BBB Industries - TSB's & Wiring Diagrams
Since this is a conversion is your wire from the ignition for relay coil (white w/ blue splotches) hot in both START and RUN positions, or just RUN?
Is the black/green wire on the relay coil grounded well (also supplies computer ground)?
The drawings show relay switched power as dark blue going to a distribution point where it changes to red and supplies the pump, injectors, computer, etc. Relay is pretty simple....battery power on one side, supplied devices on the other. Key switched power on one side of coil (must be hot in start and run), ground on the other. Key on/start, relay contacts close and power everything.
BBB Industries - TSB's & Wiring Diagrams
Since this is a conversion is your wire from the ignition for relay coil (white w/ blue splotches) hot in both START and RUN positions, or just RUN?
Is the black/green wire on the relay coil grounded well (also supplies computer ground)?
The drawings show relay switched power as dark blue going to a distribution point where it changes to red and supplies the pump, injectors, computer, etc. Relay is pretty simple....battery power on one side, supplied devices on the other. Key switched power on one side of coil (must be hot in start and run), ground on the other. Key on/start, relay contacts close and power everything.
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From: Virginia
The red wire gets power from the EECIV relay, not the computer. But the EECIV relay is activated by the computer. A hot wire from the ignition switch goes to the EECIV relay coil, and then the computer grounds the other side of the coil to activate the relay and send power onto the red wire. Sounds like either your pump relay is bad, or the computer is not grounding the wire to the pump relay to activate it. Go to the relay and ground the tan/lightgreen wire and see if the pump runs.
Here's a diagram.
Here's a diagram.
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From: Lyman, SC
According to the drawings the ground side of the EEC relay coil is always grounded, it is not grounded by the computer and only needs the key turned to run or start to supply the positive side. The computer has full time battery power as the switched main supply and key switched power (which turns it on like a radio or MSD box), and the key switched power comes through the EEC relay. If the relay relied on the computer grounding it to energize, it would never energize because the key switched power for the computer comes through the relay contacts itself and the computer would not turn on.
The computer does control the fuel pump relay.
The computer does control the fuel pump relay.
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From: Virginia
Thanks for that correction.
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From: Minneapolis, MN
[QUOTE=Franklin2;15364907]The red wire gets power from the EECIV relay, not the computer. But the EECIV relay is activated by the computer. A hot wire from the ignition switch goes to the EECIV relay coil, and then the computer grounds the other side of the coil to activate the relay and send power onto the red wire. Sounds like either your pump relay is bad, or the computer is not grounding the wire to the pump relay to activate it. Go to the relay and ground the tan/lightgreen wire and see if the pump runs.Quote]
I will try grounding that wire but I had to put the battery on the charger it was getting a little weak due to sitting for the last month, so I'll have to wait till tomorrow night to dig into it again.
I will try grounding that wire but I had to put the battery on the charger it was getting a little weak due to sitting for the last month, so I'll have to wait till tomorrow night to dig into it again.
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From: Lyman, SC
You do bring up a good point though....relay ground might not be connected if the positive side is going hot in start and run.
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A bad ground is a good bet, and easy to check. Of the two small terminals on the EEC relay, one goes hot with 12V when the key is in START or RUN, and the other would go to ground. If it's like my '85, this ground is made at a single terminal connector all the way at the battery negative post. Mine was all corroded when I pulled it apart.
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From: Virginia
There is a terminal in the self test connector that you can ground that also grounds the fuel pump relay just for this purpose (testing). Do a google search for "EECIV connector" and some pictures will come up and show you which terminal.
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From: Minneapolis, MN
I had a little but of time to check things over again tonight and I may have made things worse. I was checking the fuseable links at the solenoid, and as I was tightening the nut down and I accidentally touched both of the studs with the wrench. Now when I go to start the truck, it wont crank now 
I did check the ground off the battery, seemed good to me. That's where I'm at now, won't be able to look at it till tomorrow night.
I did check the ground off the battery, seemed good to me. That's where I'm at now, won't be able to look at it till tomorrow night.
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From: Minneapolis, MN
I may have jumped the gun a little bit, l have the plug for the clutch safety switch jumpered and it may have come off, I have not looked to verify that, but I'm guessing that's it
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From: Minneapolis, MN
I decided to check the fusible link for the fuel pump again, I cut back some insulation before the link and tested for continuity between there and the end of the link...nothing. I took a piece of wire put one end on before the link and touched the other end to the solenoid and I heard the fuel pump relay click!! Now I need to find some 10 gauge fusible link wire to repair it, but I'm so happy I finally figured it out.
Thanks to everyone who responded, it's so nice to have this great resource of information for out trucks!!
Thanks to everyone who responded, it's so nice to have this great resource of information for out trucks!!
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I decided to check the fusible link for the fuel pump again, I cut back some insulation before the link and tested for continuity between there and the end of the link...nothing. I took a piece of wire put one end on before the link and touched the other end to the solenoid and I heard the fuel pump relay click!! Now I need to find some 10 gauge fusible link wire to repair it, but I'm so happy I finally figured it out.
Thanks to everyone who responded, it's so nice to have this great resource of information for out trucks!!
Thanks to everyone who responded, it's so nice to have this great resource of information for out trucks!!
That's interesting. There wasn't any burned or melted insulation on the fusible link that burned out? I would've thought there'd be some visual evidence of what happened.
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From: Minneapolis, MN
Here's a update on my situation. Over the weekend I replaced the fuseable link for the fuel pump. I also figured out the wires to the inertia switch had a had a break somewhere, so I ran 2 new wires from the fp relay to the inertia switch.
I thought everything was good, start the truck up, it will run for awhile..sometimes a few mins, sometimes 30 secs, but never more than a few mins. The only way it will restart is to turn the key off, then try again. I tried pulling codes, but did'nt get any. I also replaced the icm with a new motorcraft part. Still stumped over this, I want to figure this out soon so I can actually drive it again, anyone have any ideas???
I thought everything was good, start the truck up, it will run for awhile..sometimes a few mins, sometimes 30 secs, but never more than a few mins. The only way it will restart is to turn the key off, then try again. I tried pulling codes, but did'nt get any. I also replaced the icm with a new motorcraft part. Still stumped over this, I want to figure this out soon so I can actually drive it again, anyone have any ideas???
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When your truck dies, is power being lost at the FP relay? What about the EEC relay? I know these trucks have an issue with the ignition switch separating such that the connector half lifts away from the contacts. I never did diagnose the specific reason why my truck would shut off randomly, only to restart and run seconds later as you're going down the road. But, of the work in the work I have in progress with it I did change out my switch and found it was indeed pulling apart; the metal crimps were starting to let go of the plastic piece that's attached to it.