were the upfitters factory installed? Which wire are you hooking into? The wires under the hood, or under the dash?
If you are tapping into the wires under the hood, they are not connected to anything, they are just bare wires that run through the firewall and terminate next to the upfitter wires under the dash.... You will need to make an additional splice.
Next step would be to test for a completed circuit at the relay. Connect a meter to the ground and wire coming from the upfitter switch as close to the relay as you can get it. Turn on the upfitter switch and see if you get voltage. Note, you need to have the ignition in run for the upfitter switches to function.
Hope this helps.