4runner

Exide Orbital, purchased from Rock Logic 4x4.
Main reason- NO CORROSSIVE ACID MESS!
Secondary reasons- high quality, higher capacity, longer life, bolted right in place of the old one.

I bought an auxiliary fuse block from NAPA and mounted it on the firewall.
To feed the fuse block, I ran a 10 gauge wire from the battery with a 30 amp circuit breaker.
Fuses feed: high & low beam headlights, on-board-air, rock lights, and the horns

I bought some Cibie H-4 replacement head light lenses from Daniel Stern at www.lighting.mbz.org.
I also bought their +30% high-efficiency 60/55W bulbs and do-it-yourself relay kit.
I wanted the DIY relay kit so I could wire and fit it exactly how I wanted. This kit uses high quality parts and saved me the hassle of trying to find them all on my own. All I had to supply was wire and a few crimp connectors.
I used 12 gauge wire to feed the high and low beams, and I also ran a new ground wire directly to the battery. This way I can run over-wattage bulbs and not worry about frying the stock wiring and the heavy gauge wiring will ensure full voltage to the bulbs for max light output. Toyota uses a ground-switched headlight setup, so I wired the relays accordingly.
The headlights I bought also have "city lights" in them that I wired into the parking light circuit.
These lights are a HUGE improvement over the stock sealed-beam lamps. Well-worth the money.

I used 2 pairs of cheapy Harbor Freight driving lights. One light pointing front and rear and one light on each axle to illuminate underneath and to the sides.
To change them from spot lights to flood lights, I removed the reflectors, roughed them up with sandpaper, and painted them flat white.
All lights are wired through one relay using 12 gauge wire. The control switch is the unused illuminated rear "deck light" switch on the lower left side of the dash. I wired the switch that the lights can only come on when the parking and/or headlights are on.

The stock rear cargo light ("deck light") is PITIFUL, so I bought a generic dome light with a switch on it from NAPA and mounted it to the rear wiper motor cover.
To power it, I tapped into the wiring for the front dome light under the driver's side kick panel. There are 2 wires there, one is the +12V feed, and the other is a wire that is grounded whenever a door is opened. I ran a wire from both of those back to my new cargo light. For a permanent ground at the light, I ran a short wire from the light to a screw on the wiper motor.
This way, the cargo light comes on whenever a door is opened, or I can use the switch on the light itself to turn it on manually when I am back there.
The light is very bright and illuminates the whole interior of the truck, not just the cargo area.

Here is where I may have gotten overly fancy...
I tapped into a wire near the air flow meter so that the compressor clutch can only be activated if the engine is actually running.
I duplicated the factory air conditioning idle-up system using parts from the junkyard. Basically there is a hose that bypasses air around the throttle body and in that hose is a valve. That valve is adjustable and turned on and off by a separate vacuum switching valve (VSV). I found out that with the throttle closed, the engine computer will make the engine idle speed fluctuate up and down rapidly if the idle speed is over 1100 RPM. To get around this, I cut the "idle" wire at the throttle position sensor (TPS) and inserted a relay. The relay is normally closed, which allows the TPS to operate normally when the compressor is off. When the compressor kicks in, the relay opens, tricking the computer into thinking that the throttle is open, thus allowing the engine to idle normally at speeds over 1100 RPM.
For the OBA on/off switch, I used a 3-way switch, and wired it so that I can run the OBA with or without the idle-up, giving me a high or low setting. I normally leave it in the high position.
Obviously there is also a pressure switch in the system that turns the compressor on and off as needed. I bought the switch from Wheeler's Offroad.

I replaced the wimpy (embarrassing) stock horn with dual Cadillac horns from the junkyard. The Toy horn was ground-switched and the Caddy horns are 12V switched, so I had to use a relay. The stock wires are attached to the control leads of the relay, and the +12V and the horn feed are on the other leads.