Your diagram is almost right. Prongs 85 and 86 is the "trigger" side of the relay. This is where your SPST rocker switch needs 12Vdc comming into it on the center pin of the switch. the left side is OK to ground if it has a light in it. If it does not have a light in it, it would then be a SPDT switch and then you would hook the center and only one other side up. In your diagram relay 30 is correct and the voltage going out of the relay sould be on prong 87 which is correct also. Do not ground the relays prong 87a. It will short things out and cause the battery to drain if the wires dont melt first. Prongs 30 to 87a are the NC (normaly closed) side of the relay. Hooking this side up is the same if there is no relay in the circuit at all and makes no diffrence (always passes current to the load. prongs 30 to 87 is the NO (normaly open side. this is the side that gets switched when 12Vdc is sent to prongs 85 and/or 86.
So here is how I would wire things. run wire from the B+ on the battery to prong 30 with a 10awg or larger wire. Prong 87 to lights + post and other side of lights to ground. Prong 87a not used. Tap splice off the cigaret lighter wire or other ignition 12 volt source that works only when the FJ is powered on and running to your switch center pin if that is not labled ground, From the right prong on the switch, then wire to prong 86 on the relay. Ground relay prong 85 to metal. A relay needs 2 diffrent 12Volt sources to work. A relay is used to switch power to two diffrent sources or used to power a source on/off when a SPST switchs current rating is less than the amp rating of the load. All your are really missing is the 12v 2nd source to go into the center prong on the rocker switch. Good luck.
So here is how I would wire things. run wire from the B+ on the battery to prong 30 with a 10awg or larger wire. Prong 87 to lights + post and other side of lights to ground. Prong 87a not used. Tap splice off the cigaret lighter wire or other ignition 12 volt source that works only when the FJ is powered on and running to your switch center pin if that is not labled ground, From the right prong on the switch, then wire to prong 86 on the relay. Ground relay prong 85 to metal. A relay needs 2 diffrent 12Volt sources to work. A relay is used to switch power to two diffrent sources or used to power a source on/off when a SPST switchs current rating is less than the amp rating of the load. All your are really missing is the 12v 2nd source to go into the center prong on the rocker switch. Good luck.