I noticed that the third brake light on the back of the topper on my '95 F-150 works when I hit the brakes and it also flashes when the left turn signal is on. The previous owner has it wired to the left tail light which is obviously the cause. My question is how do I hook it up correctly? There are a few wires under the back of the truck so how do I determine which two are the ones I need? Thanks....

 

Multimeter is a good item to have in the garage. You could use a test light too. My GFs moms topper 3rd brake light was wired into the trailer light harness.

 

The stop light circiut # is 511. The easiest thing is to tap into the one on the back of the cab. The harness runs up in the corner behind the drivers seat.

 

How do I know which wires to tap into? Is there a #511 on one of the wires? How do I get the wires from the topper to the cab-drill a hole in the back of the cab? Do I legally need the third brake light back there?

 

The 511 is light green it may change to ciruit #589(dark green) before it gets to the light. How you tap into it is up to you. Legal??? all states are different. I would think if it's there it has to work.

 

Couldn't I wire it directly into the third brake light at the back of the cab? That way I wouldn't have any problems with the turn signals or flashers....

 

Since you don't seem to be an electrical expert, that would be the best connection for you....