'96 F350 trailer exterior lamp relay - Diesel Forum - TheDieselStop.com
Power Strokes 1994-1997 General Technical discussion of topics related to vehicles powered by the Power Stroke engine in 1994 through 1997 models.

 
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post #1 of 8 (permalink) Old 08-11-2016, 02:23 AM Thread Starter
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'96 F350 trailer exterior lamp relay

Hello all, Trying to troubleshoot a wiring problem with trailer light wiring on my 1996 F350 4wd powerstroke pickup. pickup tail lights work fine, left turn, right turn, running lights fine. Trailer receptacle right turn blinks at pin with test light - fine. Left turn and running lights no power at pin with test light. Unplugged C407 connector under truck no power to pins for left turn or marker lights from main harness. Checked Fuse 4 in fuse panel - fine. Fuse 4 is described to power a "trailer exterior lamp relay". Any help to guide me to where this relay is or any clues to why left turn and marker lights at C407 connector would not have power would be greatly appreciated. Thanks, Dan
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'96 Black F-350 4x4 SRW, 5 spd, 170K miles- no rust Wyoming truck
'93 Black F-350 4x4 SRW, 5 spd, 180K miles, Installed Banks turbo @ 120K, much better! getting rusty
'79 Black F-250 4x4 SRW, 4 spd, 400M, 500K+ miles -retired out back.
'86 VW Jetta Turbo-diesel 336K retired out back
'75 LN-9000 Ford Louisville, 671 detroit, 10 spd
'74 LT-9000 Ford Louisville, 8V71 detroit, 13 spd
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post #2 of 8 (permalink) Old 08-11-2016, 11:33 AM
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It is most likely in a little auxiliary box mounted on the rear side of the under-hood fuse box. On a '97 '250 it was only there if you bought the towing package...not sure about your 350. I bought the parts from a junk yard and added it to my bare-bones truck. As I recall there is one relay for the running lights, and another for the charging power circuit...but don't bet based on my memory!

-KF-
97 '250 SC 4WD ZF5, 3.55 axles, 1.0AR volute, '99intercooler, Hypermax DP feeding 4"straight pipe, US-Gear chip, Maddog stage-1 injectors, 140Volt IDM.
"If it ain't broke, fix it 'till it is!"
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post #3 of 8 (permalink) Old 08-11-2016, 11:52 AM
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The trailer running lamp relay is in the main fuse box under the hood and is relay #4. Your turn signal lamp and trailer brake light fuses are also in the under hood box, fuses mini fuse 6&7.

Power Distribution Box

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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post #4 of 8 (permalink) Old 08-11-2016, 01:24 PM Thread Starter
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solved

Hello Kevin and Bugman. You led me to the right place. There is an aux box just behind the PDB under the hood that contains two relays. I am assuming one of these is the "trailer running lamps" relay. My problem was that fuses 4 and 7 in the PDB under the hood were burnt open. This probably occurred when I was wiring the trailer junction box yesterday. I had the 7 wire cable and plug connected to the truck and I crimped the eye terminals on the other end of the wires to land them on the terminal box mounted on the trailer. I had previously turned the turn sig and running lights on and tested the wire colors for correct. Left turn (yellow) and running lights (brown) may have hit ground (white) while I was moving the loose ends around. All wires are landed securely now in the trailer terminal box, I replaced fuses 4 and 7 and have left turn and running light power to the trailer terminal box as it should be. I plan to wire the rest of the trailer today but will leave it unplugged from the truck until all wires are landed or secured so I don't again accidently ground a wire and blow a fuse through my own doing. I will attach pics of the PDB and owners manual that show the layout of the underhood fuse panel. I looked on my 1993 F350 and it has a similar underhood fuse panel but not the aux box with the relays. Been towing with that truck for 12 years and never had a blown fuse for trailers. You learn something new every day. Thanks again for the help. Last night I was ready to start getting into the wiring harness and plugs to look for a burnt spot or bad connector. Replacing a couple fuses sure was a lot better solution to the real cause of the problem.
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'96 Black F-350 4x4 SRW, 5 spd, 170K miles- no rust Wyoming truck
'93 Black F-350 4x4 SRW, 5 spd, 180K miles, Installed Banks turbo @ 120K, much better! getting rusty
'79 Black F-250 4x4 SRW, 4 spd, 400M, 500K+ miles -retired out back.
'86 VW Jetta Turbo-diesel 336K retired out back
'75 LN-9000 Ford Louisville, 671 detroit, 10 spd
'74 LT-9000 Ford Louisville, 8V71 detroit, 13 spd
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post #5 of 8 (permalink) Old 01-06-2019, 12:35 PM
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Hello
I have a question on your attached pictures of the power distribution box and the other two relays next to it.
I Have a 1996 F250 4X4 with the same P.D.Box and the two relay's next to it. I believe those two relays are for trailer towing for adding on a 7 way connecter. Ford offers the 7 way adapter harness that plugs into the stock harness at rear of vehicle, which my truck has but no brake controller for trailer breaks.
If I add a brake controller with jumper harness to under dash connector, gray square 6pin connector with 5 wires(under center of dash bottom) and attach the brake controller red wire to cold side of brake switch i should be all set?
Problem is trying to find out about 1996 F250 wiring and what the two separate relays are for they don't show it in owners manual like yours in picture. any help would be appreciated. Thank you Bob
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post #6 of 8 (permalink) Old 01-06-2019, 01:08 PM
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If you have relay #4 installed along with fuses 4, 6, 7, and 21 installed in the under hood box and no one has cut into the trailer wiring going to the rear end you should be good to go with the trailer wiring harness installed.

For the brake controller all you need is the plug in that attaches to the factory wiring under the dash and then to the controller, you don't need to connect any other wires to the brake circuit it is already connected to the under dash harness.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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post #7 of 8 (permalink) Old 01-06-2019, 01:49 PM
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Your trailer wiring should be very similar to this (same colors & functions, but possibly different connectors & pins within the circuits):


(phone app link)


Note the links in the caption, which include free wiring diagrams. Your fuse blocks are probably very similar to this:


(phone app link)


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post #8 of 8 (permalink) Old 01-06-2019, 06:15 PM
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Shouldn't have to worry about wires or color of wires.

Everything is plug and go except for the connection from the brake controller to the wire adapter that has the plug on the end of it.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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