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2003 E250 campervan
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Discussion Starter · #1 ·
My new to me van is missing this diode in the underhood fuse box. I have replaced the long dead aux. battery and all the wiring looks good but the OEM tow plug is still dead. I am wondering ifthe missing diode has anything to with the dead tow plug. I looked online and couldn't even find a replacement diode to fill the spot in the fuse box.
I have checked all the fuses and they are good. Is there a master relay that controls all the power to the dead OEM tow plug?
 

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Phoenix, AZ 85008
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Welcome to the FFO!

There is a fuse box under the instrument panel on the drivers side. One of the fuses protects the following circuits;
Radio Capacitor(s), Ignition Coil, PCM Diode, PCM Power Relay
There is NO diode in this fuse box.
Details for the fuse box are shown in the owners manual


What is under the hood is a Battery Junction box (Or a smart junction box) has mostly relays.

I do not believe there is a diode in the tow plug.

Does the engine run?

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2003 E250 campervan
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Discussion Starter · #3 · (Edited)
Under the hood fuse box has a spot(position 29) for a auxiliary battery diode
Looks like it's being called a power distribution box and it has several fuses and relays.
Frankly, Thank you for replying but I don't think you read my post. I asked if the auxiliary battery diode has anything to do with the the towing plug. Also, if there is some sort of master fuse/relay that might be bad and effect the the tow plug.
 

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Phoenix, AZ 85008
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I don't think there is a diode in there either.
Typically, when Ford uses a diode (which is rare) it is in a wiring harness or in a component assembly.

I have attached a trailer tow harness diagram for 2003 F 250
Your E250 should be similar. No diode.

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Rectangle Slope Font Parallel Schematic
 

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Phoenix, AZ 85008
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I found a trailer tow harness for an older Aerostar that has a fuse in the harness. However, the wiring is for adding a factory pigtail to the non-tow harness system.

What part of the two plug is dead?
The turn/brake lamps
The running lamps
Or ???
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2003 E250 campervan
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Discussion Starter · #6 ·
No offense, but we still are not on the same page.
I have a 2003 Ford E250 and the wiring diagram shows an auxiliary battery diode in the PDB and mine is empty is all I know. The van has a tow pkg. with a OEM 7 pin tow plug. Nothing but the ground pin has function. No bad fuses anywhere and all relays are present in the PDB under the hood. The van itself has full function on all other systems. I read, the diode has to do with isolating the engine battery from the aux. rear power battery, but I'm not sure.
 

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Phoenix, AZ 85008
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OK

I do not have a complete wiring diagram for your model
Just attempting to help with the limited resources

I don;t know where you read about that diode. You might go back to that reference.
Aux rear battery? Not sure where that would be other than a trailer battery in the trailer.
A diode would not make sense for that application in isolating the trailer batter from the vehicle battery.( Breaker or a BA fuse, for circuit protection.) Mostly because once the tow is done, disconnecting the trailer from the tow vehicle is almost universal.
A diode only allows current to flow in one direction. For the kind of current that is possible between batteries of the TV and trailer the diode would have to be very large.

Many Econolines had a second (optional) battery and that was under the hood. And some has dual alternators. None had a diode. An isolator or a solenoid sure. Just not a diode.

I think you need to go back to the reference.

As to why no power to trailer tow pig tail, there are two different circuits. Both with fuse protection. The turn/brake ciruit and the running light circuit. The pigtail has a connector not too far from the end. That would be a likley place to check for dirt and debris.

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Discussion Starter · #8 ·
FYI, the aux battery is OEM on the rightside frame rail. IMHO, A complicated wiring system with undersized wiring, a pain in the butt location for servicing and bunch of relays in the PDM.
Quest to be continued. My struggle is real. haha
 

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in your pdb, with t.s. on, is there power at fuse 5 and six?also with running lights on, power at 14? if so, you have a wiring problem
also, for battery power to the trailer bat. the ground connection in the plug needs to be grounded to activate the relay
 

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Discussion Starter · #12 ·
in your pdb, with t.s. on, is there power at fuse 5 and six?also with running lights on, power at 14? if so, you have a wiring problem
also, for battery power to the trailer bat. the ground connection in the plug needs to be grounded to activate the relay
The OEM 7 pin tow plug was dead when probed. I hooked up my towed's(Jeep) umbilical cord and low behold the tow plug has full function and Jeep lights work properly. Still haven't found out why there is a empty spot in the PDB for an auxiliary battery diode. No matter everything works.
 

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Thanks for posting back

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