Hi,
Mrwurm asks:
<font color=blue>What function does the relay perform? I've wired up a lot of lights and never used one. What will it do for me?</font color=blue>
Provided that the switch you use is rated for the current it will break, then the realy will do nothing but complicate the wiring, in the tractor work light application, in my opinion.
An example where a realy is really useful, is in a higher voltage circuit, where you want to control to be a lower [read safer] voltate. Such as control of a 480 volt motor, using 110 volts going to a start/stop push button.
For the simple control of work lights on the tractor, if you have an on/off switch that is rated for the current, a simple switch should work fine. If it would eventually fail, cheaper and easier to just replace it when that happens. My guess is that it will be years before that failure happens.
Now if you try to exceed the switch rating, then you can expect rapid failure. You will not notice any difference in light brightness whether you use a relay or switch...unless there is a problem with the device, and in that case you will also develop heat at the failure point, if the lights are dimming. That power taken away from the lights has to be used somewhere...
That's the way I have seen things happen, for what that's worth.
Bill in Pgh, PA