Hi, <!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]-->
<style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> I have a 2002 F350 crew cab 6.8L V10 engine with low voltage at the trailer plugs (both 4 and 7 pin). All fuses under the dash are OK. I thought it was a grounds problem, so I ran a jumper from the battery negative back to the plug then tested the voltage. With the hazards on, I was reading around 8.5 volts from the right and left pins. I then disconnected the trailer pig tail (by the spare tire) and repeated the voltage test, same results. I have both the Hayes and Chilton manuals for this truck and they said this is an auxiliary fuse both behind the clove box for the 2002 year only. I pulled the glove box out and there is no fuse box. Plus I check for a fuse box under the hood. I only found the small relay boxes (taped shut from the factory) by the driver side hood hinge. Would this be the Aux fuse box and would be the problem?
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PS, what is the typical voltage (12 or 14) from the truck to the trailer?
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Thanks,<o></o>
Jeff

 

With the hazards on you will be getting an intermittent voltage. (If I am reading your posts correctly). With my meter it doesn't go all the way to 12 volts before going back to zero. Do the lights appear to function correctly?

 

Flashing lights and auto-ranging meters can be a headache. If your meter has a peak feature or manual ranging, it will be handy for this testing. I think our trailer fuses are under the hood in the small fuse box, the main fuse box is under the steering column.

A bad connection can cause a voltage drop, pull your fuses and test them with your meter. Then make the tabs shinny before reinstalling them.

 

hay Jeff, I had an intermitten issue with mine once, it drove me nuts, I checked everything and sometimes they would be weak voltage.

I accidently noticed that the trailer pulg at the rear of the truck is a plug in, there is another pulg in behind it. mine had corroded the sel went bad, when I pulled it apart it was no wonder I was having intermitten issues.

hope this helps

 

Thanks for the info.
I do have a high voltage (max) feature on my multi tester. With the flashers go on and off, this is the only way to gain the peak voltage. Just to confirm my problem, non of the trailer lights are working. I even re-attached the ground wire on the trailer frame. I may re-pack the wheel bearing to see if that would help (just kidding).
I also checked the second wire connection behind the rear bumper for corrosion, it looks fine.

I will check the relays under the hood once the rain stops.

 

Scubadog.... I am having this very same problem right now and have started a thread on it in the Misc. section under Electrical. The heading is trailer wiring issue. I have had some good info given to me, although I havent had time to get back to my truck. I have taken apart all of my wiring, but now bohiaa has me wondering if I missed one.

Good luck

 

RFD_ Truckie,
I read your thread. It sounds like the same problem. One thing I would recommend is checking the trailer grounding point on the truck just above the rear axel. Disconnect/clean, and then re-connect. The wire should be a white 10 ga wire. I need to check my relays under the hood.

 

I think I found the auxiliary fuse box #4. There are two small relay/fuse boxes under the hood on the driver’s side. It’s the one closes to the left fend. With the turn signal on, I had power (on/off) going to the relay, but no power coming out to the trailer plug. I will buy a few new relays tomorrow at the local Ford dealer and hopefully close this problem.

Let me know if this sounds correct.

Now it’s time to work on the 1980/1977 F250. I have a 1973 460” engine in it that makes tons of power (2 truck pulls so far).

 

Scuba, Yep, sounds like it. I found my relays were good, followed the wires to where they plug into the rest of the rear harness, and that was showing good to. I hope that is your problem. I have already changed my relays with no luck. I hope to find it soon, its almost time to go camping....

 

Check the back of the plug.Disconnect the connector at/behind the 7pin socket.
Ford has a repair kit for this exact problem.The connector and wires get corroded and broken.

 

If you want to test the relays, just swap them around. If some things start working and others stop, you know the relays are bad. Or you can bench test them with a 9v battery.

 

Prior to buying new relays, I performed a bench test on the RH & LH relays. I put 12 volt power to the two terminals (to make it click), then checked for continuity. I do have continuity, which means the relays are working (right?). I put the relays back in the small fuse box under the hood then checked for voltage behind the mounting box. I now have voltage.
I will re-check for voltage at the rear connection point about a foot in front of the rear bumper.

 

Yes if once clicked, you have continuity on 30 and 87 the relay is good. It was probably a bit of build up on top of the relay contacts that got cleaned as you pulled them out.

 

I still do not have 12 volt back at the trailer plugs. I will craw under the truck tomorrow to re-check the grounding wire to the frame and the trailer plug connector behind the rear bumper. If I can’t figure this problem out tomorrow, I will need to take this into a shop. I need to tow a trailer this Sunday.

Jeff

 

Jeff, I found my ground... I think. I found a Black ground wire right where you said it would be, cleaned it and reattached. I was hopeful it was something simple that I just overlooked, but no luck. Still no trailer turns/brakes. I should have opened the loom to double check, but, Had to go pick up the kid. I too am at a loss. I am tempted to think its that portion of the wire harness, and am tempted to buy a new one and just plug it in to check it.
Keep us posted...

Thanks