There are several vehicles that require a bit of alteration for some reason before connecting the trailer harness to make the output operational. Japanese vehicles have this in some cases and this is a post on Fords.
Hope it helps! BCB
” I run a Puma and pull it a 2001 Ford Expedition, there is a relay that needs to be purchased from your dealer, it’s rather cheap and worth it in the long run. It goes under the hood on my 01, I am sure your 02 is very similiar. I looked in my owners manual and found the missing relay spot, it is either #201 or 203, both deal with trailer lamps and the 203 is the backup trailer lamp. It did not come installed on my 01 Expedition. I purchased it (part# F57B-14B192-AA) from the parts dept. at my local Ford dealer, it is the same as the other relays in the other spots and since installed it locks out the brakes everytime as they are triggered by the reverse lights if I am not mistaken. I can back up in any situation flat or steep without an issue. Hope this helps, “
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