Trailer towing electrical help
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Senior User
Joined: Feb 2000
Posts: 162
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From: Denair, California
Trailer towing electrical help
I was looking under the hood of my new 2004 truck and noticed some wires on the driverside at the firewall (blue, red, white and black) what are these wires? Are these wires part of the brake controller plug-in under the dash? That plug-in under the dash has blue, red, white and green.
Also looking at the instructions that came with the plug-in, it shows that the 7-way plug at the hitch has a trailer battery feed, is this the constant hot to charge my trailer batteries as I'm towing? Anybody that could help would be greatly appreciated.
Tom
Also looking at the instructions that came with the plug-in, it shows that the 7-way plug at the hitch has a trailer battery feed, is this the constant hot to charge my trailer batteries as I'm towing? Anybody that could help would be greatly appreciated.
Tom
Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
Trailers with electric brakes are supposed to have an on-board battery that applies them in the event of an unscheduled trailer disconnect. ;-(((
I think the original purpose of that wire was to keep that battery charged, but who can dictate what the battery on a trailer is used for?
Bottom line, yes, you can charge your trailer's battery with that line. It's meant to charge a battery.
I think the original purpose of that wire was to keep that battery charged, but who can dictate what the battery on a trailer is used for?
Bottom line, yes, you can charge your trailer's battery with that line. It's meant to charge a battery.
Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
Oh, yea! The owner's manual was a "great help"! At least it told me that there were more relays than were actually in the box, and I now know that I need to install another fuse if I ever want voltage to appear at the "battery charge" pin on that connector.Guess my question should be: If you have a 2000 PSD with the factory tow package, do you have three "doghouses" surrounding your under-hood fuse/relay box?
SpringerPop
SpringerPop
Cargo Master
Joined: Aug 2002
Posts: 2,117
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From: Over Yonder, MN
I don’t have a super duty, but I did run into the same problems. When I first got my truck it had the factory 7 pin harness. Sadly, it was a mess… the ground was dead and I too was missing relays, specifically the battery charge and backup lamps relays. When all was said and done I had to trace through the harness and buy some relays to get it working right.
Cargo Master
Joined: Aug 2002
Posts: 2,117
Likes: 8
From: Over Yonder, MN
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Senior User
Joined: Feb 2000
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From: Denair, California
As stated in the original post, four wires on driverside near firewall, coming out of harness. The ends are not connected to anything.
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Joined: Jan 2002
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From: La La Land
These are most likely the "user access" wires. That's what Ford calls "spares". They're there for your own use to do whatever you want to with them. The other ends are under your instrument panel.
Fleet Mechanic
Joined: Oct 2004
Posts: 1,496
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From: Simpsonville, KY
stop, stop.... the harness in your glove compartment has those four colored wires. Those wires off of the harness plug into the aftermarket brake box, then the plug on the harness plugs into the port under the steering wheel. You do not tap into ANY wires on the truck in the cab. You use the plug, nothing more.