A length of 18AWG stranded wire, some 1/8" heat shrink, two 1N4004 diodes, T-strippers, a heat gun and a soldering iron are a cheap solution if all you want is a simple fix for Toyota's goof of not incorporating these map lights in the dome light circuit in our 4Runners. I ran my wires through the headliner, so I didn't even have to mess with the fuse block or A pillar. Just have to drop the map light / sunglass holder and the middle dome light, and fish the wire through the headliner - I pulled mine to the driver's side of the sunroof.
These circuits are ground switched, not 12V switched, so with that in mind, tie in to the dome light overhead by finding the switched ground that turns the light on with doors opening and/or unlocking, before the ON/OFF/DOOR switch. Splice in and insulate one end of the 18AWG wire with solder and heat shrink.
Pick a point where you want to split the wire into a Y (my choice was right above the map light panel) by soldering the two diodes' cathodes (the leads with the silver indicator) to the wire coming from the dome light, and solder two lengths of wire from the two diodes' anodes to the ground switched input on each map light, obviously using heat shrink to insulate any bare wires / leads. The diodes prevent back-feeding the dome light if and when you turn on each map light, and also prevent the map lights from turning both lights on when either switch is turned on.
The most challenging part for me was figuring out how to physically tie in to the circuit for turning the map lights on because the map light switches plug directly in to a circuit board inside the map light panel with no wire to splice into. I ended up using a couple leads from a resistor, soldering them to the ends of the wires coming from the diodes, and sticking them in the socket of the switch assemblies on the switched side when plugging the switches back in.
Functionality is as follows:
-Unlock 4Runner, map lights fade up with the dome lights, and fade back down when they time out.
-Open door, they fade up with the rest of the dome lights until 30 minute timer times out, or all doors are closed, and then they fade out with everything else
-Switch on center dome light (ON/OFF/DOOR) has no effect on map lights' dome light function
-Map light switches have no effect on each other or the center dome light
If you want to get fancy and add a switch to the map lights' dome light function, just put a switch in line with the single wire before the diodes and find a good place to mount it. You could always go overboard and put a switch on each map light to be able to independently switch them into or out of dome light mode. It's your project, man. Rig it any way you want!