Truck Wont Turn Off

[1-PU70]

Here is what I have fore background info. I took the switched hot wire that was running to my HEI (been that way for years) and used that wire to switch a relay for power to the HEI. Worked fine for about a year. Now here is the problem. When I turn the key off the truck keeps running. This is what I checked. The relay workes fine when the truck is not started. Turn key on relay clicks and switches on. Turn key off and relay clicks and turns off. But when I start the truck and then turn it off there is still some juce at the wire that turns the relay on and off. I used a test light to check the wire that switches the relay and when I turn the truck off from running the the test light glows just a bit. So ther is just enough juce to keep the relay from switching off. What can cause this. I dont think its in the Ignition switch (could be wrong) because it works fine without starting the truck. Could it be feadback from the alternator. Or could it be something else. Need some help. How would you check for alternator feedback anyway.