Replace a Switch with an Outlet

[Amaranth]

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.

 

[Lister1987]

Red Black and White tells me non-uk. What are you looking to plug into the outlet?

Certainly over here you could (although not best practice) feed a lighting circuit off a socket circuit and fused connection unit - The FCU would blow before the socket circuit breaker but I don't believe it has ever been done the other way around as most lighting circuits here are 6A and our appliances are either on a radial (10,16,20) or a ring (32).

I can't see it being permitted what you're wanting to do as you would be overloading your lighting circuit.

 

[Amaranth]

Red Black and White tells me non-uk. What are you looking to plug into the outlet?

Certainly over here you could (although not best practice) feed a lighting circuit off a socket circuit and fused connection unit - The FCU would blow before the socket circuit breaker but I don't believe it has ever been done the other way around as most lighting circuits here are 6A and our appliances are either on a radial (10,16,20) or a ring (32).

I can't see it being permitted what you're wanting to do as you would be overloading your lighting circuit.

Yes, non-UK. South Carolina, to be specific. It's a 20A circuit, and I want the outlet to power a stand-up freezer. I've done some more thinking about this and I bet I'll need to re-wire the light fixture and probably the remaining switch. And in fact, as I was writing this while leafing through a wiring book I came across the exact circuit map for my configuration. I think I'll be in good shape. If things go awry tomorrow I'll post another note.

 

[littlespark]

No. OP isn’t UK based, so wait for @Megawatt to read.

AFAIK, in America, outlets and lighting can share a 15A radial supply, so it should be possible.
The diagram unfortunately doesn’t have enough cores.
The far switch needs 3 cores to operate the 3 way switching, plus a neutral for the outlet, plus the ground wire. 5 in total.

By making the first switch a simple 2 way, you get a spare core to the light can be hot, the conductors from the light to far end switch can be reconfigured to give a hot, neutral, ground and an unconnected spare core.