Head lights won't turn off when truck is turned off

The other day I made a couple of stops and when I returned home I had realized that my head lights would not shut off when I turned off my vehicle. In the interim I had disconnected the battery until I could begin troubleshooting the following day. First I had disconnected the wiring harness from the cab portion to see is the issue was in my cab but I had found that the problem was still there. Next I checked all the connections and grounds for corrosion that may be causing a faulty ground and all seems fine. Lastly, (should've been my first place to look) I examined the fuse box and was able to disengage the lights by removing the 15A fuse. After some continuity testing, I am suspecting the starter relay found between the battery and the fuse box. I have no idea how to test this relay and I as suspecting that the relay is permanently fused in an "on" state and therefore won't disengage once the power has been removed. Before I go and purchase a replacement starter relay I am inquiring as to whether or not my suspicions are accurate. Please advise and thank you in advance for any assistance.

Regards