Backup lights backup light stopped working and I don't know where to find the fuse or fuse link, I looked in both the fuse block under the dash and in the engine compartment left fender aprin

Check all fuses under dash and under hood with test light.Check fuses in place.Turn ign and light switch to on when checking fuses.

There is a small fuse in the cab fuse block ,for the insterment panel that is verry easy to miss if you don,t look close ,it is hidden kind of at the top of the fuse block behind the wires,

check the neutral safety switch move the shifter around and see if the lights flash

should be under dask or when doors are poen look for panal on side of dash or fuse box could be under the hood useually on drivers side,,look for black box with cover..

to know if the relay is working you can either check the wires with a meter and checking for power coming out of the relay when the switch is acitivated or you can hold a car stethescope to the relay to hear it switch on. to check if its the switch you would have to use a meter to check for power coming out of the switch 12volts dc ofcourse.all thus fails buy the switch you can always return it right?

It sounds like a blown fuse. Are you checking them with a test light? And have you located all of the fuses. there will typically be a fuse box under the drivers dash area, and one under the hood. have another look Im certain you'll find a blown fuse. Good luck.

If you have check the fuses inside and out,WITH A TEST LIGHT,and have power on both sides of each fuse,then there are a group of fusible links,they are under the hood on and mounted the fire wall on the passenger side.

It may not be a fuse at all it sounds from the description (14a) it is a 14 gauge fusible link which is a wire that will burn out like a fuse, check for 12 volts with a multimeter or test light from the fuse box and then continue down the circuit until you cannot find power. Just before this point you should be able to see a part of the wire that looks different and that should be the fusible link.

Check these;
Brake lights, backup lights. cabin lights.
None of these are controlled by the light switch which seems to be the problem. You may need a voltmeter to track this down.

A long shot is to check the fusible links under the hood. They are essentially fuses by another name. They are sometimes located in gang boxes and even one of the '+' cables coming off the battery if it has two cables.