I just bought a '97 F-150 extended cab w/3rd door/fleetside bed w/factory towing package. I also just bought a 30' camping trailer and I'm trying to get the wiring for lights and electric brakes working properly. The problem I have is the factory trailer harness was cut right at the back of the plug by he previous owner and I bought an after market 7-pin harness to replace everything up to the truck wiring harness plugs. The AMH I bought has a larger plug for the plug-in at the back of the truck than what's on the truck, its a 4 wire plug. I traced the wires and cut the larger plug off and wired it to match the wires going to my tail/brake lights. When I tested the lights and electric brakes everything works until I turn a blinker on, doesn't matter whether its right or left, and hit the brakes the blinker stop blinking. Can anyone please help me solve this problem? Thanks.

 

Respectfully, you have a bigger problem than the wiring.
The trailer is too large for your 97 F150.
Better reconsider the tow vehicle size of at least an F250 with the larger engine and gear ratio.
For info, look in the owner manual page 120 for towing weight specs.
Specifically the Gross Combined Weight rating for the truck and the trailer fully loaded is about 11,500 lbs. +/- depending on the truck's equipage.
The trailer weight is not the governing spec but the total weight of both.
Here is the example using weight figure in the range for both.
Truck weight at 5200 lbs loaded with gas, passengers and any weight in the box.
Trailer at 7500 lbs lightly loaded.
5200 + 7500 = 12700 lbs. This combined weigh will be over the limit for nearly all F150 size trucks.

Your going to find it hard to tow that size trailer with any speed, comfort and reliability.
If you still do it, be sure the tow hitch is rated for the job, is not rotted out underneath, truck rated tires, and brakes are in first class condition.
.
By the way, a 4 wire plug will not service a trailer with electric brakes.
It needs the 7 wire round plug harness plugged into the factory harness under the truck., an additional relay and fuse in the engine bay. The trailer needs an emergency brake battery and the lead to keep it charged that is supplied through the larger trailer plug and wiring. A good trailer controller in the cab.
Clearly., anyone who cut up the trailer plug wiring was tying to defeat the system, if not for repairs.
Good luck.

 

Bluegrass the trailer is not too big. It had a factory 7-pin harness that the previous owner cut and installed the 4 wire plug. The truck has the factory heavy duty package installed with electric brake wiring. I need to find out why the blinkers quit blinking when you apply the brakes.