I have a 1998 ford f 150 and can't get the trailer turn lights working. i checked the fuses all are good so I think it's a relay but I don't know wich one is for the trailer turn lights and the book doesn't say. so does anyone know which relay # i need to check and is it in the panel inside the truck or one of the three boxes under the hood?thank you in advance

A 1998 has the engine mini fuse panel installed, but it is not documented in your owners manual. Don't know why this is.

You would want to open the engine mini fuse panel, and check the 20A fuse.
This is a picture with the relays documented, as this is not covered in either the 1997 or 1998 owners manual.


Chances are the fuse supplying power to the L & R trailer tow stop / turn relays is blown. Common source for this problem, but could also be the relays ( possible but not probable that both went at the same time ).

You can download the 1997 Owners manual and get the page that has the engine mini fuse panel picture and info.
https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

If you have never towed or used the trailer plug before then I think you are in the right area. On vehicles equipped with a towing package, Ford shipped the vehicles with a loose parts bag. In this bag (and depending on model, equipment, etc) were relays/fuses/connector plug and some instructions. The relays/fuses were to be used to energize the trailer connection and were fitted to a relay/fuse box under the hood. If you have the owners manual then you should be able to locate a layout of that box and determine if the relays/fuses were ever put in place and if not then acquire them from a local parts store or your dealership.