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Old 09-18-2017, 06:44 PM   #1
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Help find cause of power loss to towing vehicle's 7-way plug

Hi, please help me consider common faults to look for...my towing vehicle, a 2002 Ford E-350 van has lost power to the 7-way plug. I first checked the fuses the Ford manual says are reserved for towing lights, etc. and those are OK. Then, checked every. single. fuse. in the boxes. All are OK.

I looked at the wires and can't find any breaks in them. I'd appreciate any hints you can give me. It cannot be so friggin difficult to find this fault so I',m really frustrated.

For information, know that nothing works when plugged into the trailer. No lights, signals or anything. The electric brake control in the pulling vehicle shows there it power to it, but when plugged into the trailer, it is not getting the feedback signal showing any connection.

The 4-way plug on the same harness also has no power whatsoever.

Thanks for any suggestions!

Tom
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Old 09-18-2017, 07:38 PM   #2
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Did you test directly to chassis ground?
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Old 09-18-2017, 10:04 PM   #3
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Ground is something to study
Sounds like something came unplugged.
I just had a 3 day episode searching for a blue wire,
Was running a tow trailer wire to the back of the 97 f53 chassis. I was told there is a plug back of chassis by rear wheels .and I'm told a harness is avalibele to plug into factory harness.
Something to ck and see if one was used .


I did not go that rout but I would look at the plug-ins from back to front.
Take your test light and start looking
Would not think it's going to be a major thing

Good luck .
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Old 09-18-2017, 11:21 PM   #4
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You could check the plug ends of the umbilical cord. I had an occasion where one of the wires came loose in the plug.
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Old 09-19-2017, 05:09 AM   #5
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Tom-

See this diagram, from the 2002 Ford Body Builder Layout Book.

It shows there should be two connectors inside the left frame rail at the rear. Ford sells a harness that plugs into those connectors and terminates in a 7-pin hitch connector. You can also buy an aftermarket harness, such as this one.

Neither the Ford nor aftermarket harnesses have a four-pin connector in parallel with the 7-pin, so it's possible your van is wired differently than the diagram shows. etrailer specifies a harness for a 2002 E-series that uses a round connector. It has a 4-pin in parallel.

In any case,

1) check the signals with a voltmeter attached to a known working ground (per post #3)
2) trace forward from the 7-pin connector, looking for the two Ford connectors or any other connectors within three feet of the rear of the van, to see if any have become dislodged/shorted/etc.
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Old 09-19-2017, 10:51 AM   #6
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Quote:
Originally Posted by l1v3fr33ord1 View Post
Tom-

See this diagram, from the 2002 Ford Body Builder Layout Book.

It shows there should be two connectors inside the left frame rail at the rear. Ford sells a harness that plugs into those connectors and terminates in a 7-pin hitch connector. You can also buy an aftermarket harness, such as this one.

Neither the Ford nor aftermarket harnesses have a four-pin connector in parallel with the 7-pin, so it's possible your van is wired differently than the diagram shows. etrailer specifies a harness for a 2002 E-series that uses a round connector. It has a 4-pin in parallel.

In any case,

1) check the signals with a voltmeter attached to a known working ground (per post #3)
2) trace forward from the 7-pin connector, looking for the two Ford connectors or any other connectors within three feet of the rear of the van, to see if any have become dislodged/shorted/etc.
My 98 said the connectors are right where you say they are .however on mine.
The connector is right in middle of frame rail boxed frame rail (from my maker) and gas tank
I can't get to it without dropping tank.
I was looking for the blue trailer wire. I just ran a new one .
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Old 09-19-2017, 12:42 PM   #7
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I can't determine how you've determined there is no power, other than your statement that nothing works on the trailer when plugged in... So, let's start at the basics. get an ohm meter and let's ohm out your harness between the tow vehicle and the trailer. I just replaced one that had no apparent breaks BUT, was pinched and broke wires internally. Next, validate the grounds on both the trailer and the tow vehicle from their respective connectors to their physical termination on the vehicle and trailer. The connectors are extremely susceptible to corrosion. IF the harness ohms good, the grounds check good, (and you said all the fuses are good) then open the back of the connector on the tow vehicle and check power at the physical termination on the connector. If you do not have power there and through to the front of the connector it's time to trace the wires back on the tow vehicle. Four biggest issues are fuses, grounds, broken wires and corrosion... IF you DO have power at the tow vehicle connector then it's time to trace the wires on the trailer from the connector connections down stream...
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Old 09-19-2017, 04:22 PM   #8
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Thanks, everyone! You've got some good tips and will work on these.
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Old 09-20-2017, 04:29 PM   #9
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Did you turn on the salesman switch. ?
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Old 09-24-2017, 12:54 AM   #10
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salesman switch?
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Old 09-25-2017, 06:59 AM   #11
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Many trailers have a master switch in line from the battery to the trailer to shut off the power. It's often called the salesman switch it is to keep the battery from going dead. When it's not used. Some go as far as to put a solenoid switch in. My Fun Finder X is like that.
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Old 09-25-2017, 08:36 AM   #12
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Our switch is in the front pass through compartment of our trailer. Ours is a dial type switch. 1/4 turn in either direction for off and on.
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Old 09-29-2017, 08:47 PM   #13
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Woohoo! Thanks, everyone!

Hey, here's an update for you. Thanks so much for the kind and valuable advice.

I used my tested the voltages again while referencing the wiring diagram for the plug. I got really erratic readings--I thought my meter was broken.

So, I found the factory plug under my van and by unplugging it was able to check continuity between the plug end and the, well, plug end.

What I discovered was that I was getting erratic readings, that way, too.

When I tested voltage on the live end of the unplugged cable, readings were pretty stable.

Long story short, there was apparently enough corrosion in the aft end of the cable to cause erratic connectivity.

I bought a new plug and cut an inch off each wire and reinstalled. Now, my lights and electric brakes work fine.

Thanks again for your help!

Tom
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