Factory trailer plug-7 way
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Factory trailer plug-7 way
I have a 90 F250 with a factory wiring harness to a 7 way trailer plug. The #3 pin is 12v (always) hot pin. My trailer monitoring panel does not show the batteries charging while the engine is running, but it should. The trailer place tells me the number #3 pin should be coming from my alternator. How can I check to see if it is in fact from the alternator and if it is throwing out a charge to the coach batteries? Any help is Greatly appreciated.
The 7 plug pins are all connected right and all other functions work.
Can any hot wiring serve as a charge wire? Sorry to ask but I just don't know.
The 7 plug pins are all connected right and all other functions work.
Can any hot wiring serve as a charge wire? Sorry to ask but I just don't know.
Senior User
Joined: May 2004
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The power wire for your trailer plug comes right off the battery side of the starter solinoid, witch will charge your trailer battery when the truck is running. If you are getting power at the truck side of the trailer plug, you might want to check your trailer connector for corrosion in the plug.
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You should have about 12.5 volts with engine off and 14.5 with the engine running. These are not exact numbers. These are arbitrary numbers just to make the point.
I can't think of any part of your truck wiring that is isolated from the charging circuit.
Grounds to trailers are always one of the first things to check. If your ground is not perfect you get flaky problems.
I can't think of any part of your truck wiring that is isolated from the charging circuit.
Grounds to trailers are always one of the first things to check. If your ground is not perfect you get flaky problems.
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I don't have the diagrams in front of me me but it seems to me that on my "87, there is a relay on the driver's side inner fender near the firewall used for controlling power to the trailer...
Ooops!
I just reread your post, you're talking about the pin that's always hot, never mind..
I gotta agree with HardScrabble then, clean all the connections in the loop. The alternator only raises the voltage about 2 volts, there's probably a dozen splices/connectors/terminals between the trucks battery, your trailer's battery, and back to the trucks ground. Just a tiny voltage drop accross any of them and you don't have a lot left to charge the battery.
BigFrank
Ooops!
I just reread your post, you're talking about the pin that's always hot, never mind..
I gotta agree with HardScrabble then, clean all the connections in the loop. The alternator only raises the voltage about 2 volts, there's probably a dozen splices/connectors/terminals between the trucks battery, your trailer's battery, and back to the trucks ground. Just a tiny voltage drop accross any of them and you don't have a lot left to charge the battery.
BigFrank
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Where can I get the pigtails to hook-up to my factory trailer wiring on my 1991 F250? My ford dealer is very reluctant to look up anything after I say 1991.
I have a round plug by the emergency brake with three wires to hook to a brake controller and two square plugs back at the back bumper for a 7-way.
I hate to cut into the factory wiring unless I just can't get the connectors.
I have a round plug by the emergency brake with three wires to hook to a brake controller and two square plugs back at the back bumper for a 7-way.
I hate to cut into the factory wiring unless I just can't get the connectors.
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