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I have a 2008 F150 XLT SuperCrew 4X4 that I bought new, I have towed a few boat's and utility trailers over the years but non with electric brakes. I'm getting a trailer with electric brakes and have a question. The truck has factory tow package with both 4 flat and 7 pin connector. I have checked the fuse box in the cab and I think everything is there except the full iso relay for the battery charge does anyone know what this does because there is also a fuse that is already there that says the same thing. And if I need this does anyone know the part#
Thanks in advance
Do you mean all your trailers you have pulled have electric over HYDRAULIC brakes ??? I'm thinking you meant they all have had ELECTRIC brakes that plug into your 7 (or 4) pin connector. What is this NEW trailer you are getting? Does it have electric brakes which is the industry standard or electric over hydraulic? If just standard electric brakes you are already OK to plug it in an tow.
Sorry, I can not help you with your question about this " iso " relay.
I think you are fine with what you have. Did your truck come with the Ford TBC? (Trailor Brake Controller) installed? If it did NOT, you will need to install the missing relays. Available either from Ford or also available on Amazon, Auto Zone etc. The info will be in your owners manual. If that is missing, you can download one from Ford.com
I remember when I got the truck it came with some parts in the glove box for the tow package and I believe I installed what ever it was but can't remember for sure, I have slept a couple of times since then. According to the fuse chart in the owners everything is there except the full iso relay. And I have been looking at brake controllers because I don't have one now. Just wondering what the relay does and if anyone knows the part#
This is the wiring diagram I found for your truck (you didn’t state the engine size but that shouldn’t affect the tow circuit wiring.)
Can you provide more specifics on the relay you’re looking for? The diagram provided in service info for the smart junction box doesn’t list a “Full iso relay” so I’m wondering if your owners manual lists a fuse number that powers the relay in question. If it does, I can trace the circuit in the power distribution diagrams and maybe find some more info about it.
I stood on my head a couple of days ago and looked in the fuse box on the passenger side and the book said it is spot R05 "trailer tow battery" and it's a full iso relay. I have the 5.4 engine in a XLT. If I remember correctly the R04 and R06 were also the same type of relays
I stood on my head a couple of days ago and looked in the fuse box on the passenger side and the book said it is spot R05 "trailer tow battery" and it's a full iso relay. I have the 5.4 engine in a XLT. If I remember correctly the R04 and R06 were also the same type of relays
Ah - now it’s making sense.
ISO = International Standards Organization - all that means is the relay meets ISO production standards. If the relays on either side are the same type/size, just take one into the parts store to match it up. It doesn’t have to come from Ford.
The battery charge circuit (also called a 12v or battery supply circuit) does exactly what it sounds like - provides battery (charging) voltage to the trailer plug. Most trailers with electric brakes are required to have a breakaway system installed to apply the brakes in case the trailer comes unhooked from the truck.
The breakaway system is powered by a battery, so to make sure the battery is ready to apply the brakes when needed, a charging circuit is routed to the trailer. The same circuit can also be used to power a winch, lift motor, work lights or other 12v accessory on the trailer.
Whether or not yours needs a breakaway system is dependent on weight, use (commercial or private), and state regulations - you’ll have to contact the local DMV to find out. If it’s not required, you don’t need the charge circuit unless you want to power an accessory on the trailer.
I knew I had it
Dug thru my toolbox today and found the original package that came with the truck. It has a pigtail for a brake controller and the relay.
Thanks for the help and sorry to waste everybody's time.
BP is right, we all learned something. Also do not buy a cheap, Auto Zone, O'Riely's, or similar electricals as you could have some real issues. Several years ago I bought a cheap relay from Auto Zone to replace my fuel pump relay to come out an hour after I had gotten to my buddies job site and gas was running out of the valve cover on my truck, pumped a half a tank, 20 gallons, through the engine.
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