I'm a DIYer and first time poster. I've got a three-way switch and light fixture in my garage as shown in the attached .pdf. I want to replace the downstream switch with an always-on outlet. (Or I can change the single-gang box to a double-gang and just add an outlet next to the switch.). I've tried capping off the black wire and attaching the red and white wires to the outlet but when I did my GT-10 tester said I had a hot & ground reversal error in the first case and an open ground error in the second case. And in both cases the remaining switch did not turn on the light. I appreciate any help anyone can offer.