auxiliary reverse light switching

The diagram in the other thread does exactly what you want it to do.  The only problem with it was a not so exact layout of the switch.

You will need to get a SPDT (Single Pole Double Throw) ON-OFF-ON switch.  Toggle or rocker but it has to be an on-off-on, and it can't be a momentary either.  Generally on this type of switch the center connection is the common connection. In your case the output to the relay.  The 2 outer connections will be the the input to the switch.  With the switch in the middle position it will be off.  In one position it will get the constant 12V and turn the lights on.   The other position will get power when your reverse lights are on, thus turning on your aux lights.

https://www.the12volt.com/installbay/file.asp?ID=665

My extra lights are about 8amps and the reverse lights are at 7.5amps. Is the line running to the reverse only to enable the the relay to work when in reverse?

if your stock lights are 7.5 amp and u add an 8amp light load, of course your going to blow fuses. THe line running from the reverse is from the relay, not to trigger the relay. its wire for reverse lights only. What i suggest you do is add another relay from your reverse light wire to tirgger a relay so it can be isolated on its own.

relay wiring

85 - Ground