We apologize up front for the next part as it's a bit confusing at first. Schematics for adjustable regulators flip the pins around. But it's not random; it's actually the simplest way to show what goes where. Like the fixed-regulator schematic, it reads from left (power in) to right (power out) and from top (positive) to bottom (negative). Here's how it looks:

Complementary Transistor
Regulators typically handle 1 to 5 amps. But some applications, especially heater fans and old tube radios, can draw more than even the most powerful regulator can handle. Technically, you could combine the outputs from several regulators but the following shows a more elegant way.

The following transistor complements the regulator's voltage output, only with a lot more current capacity to back it up. Even the inexpensive 2N3055 from Radio Shack can handle 15 amps. That's enough to run a full deck of gauges and a blower motor at full speed and a tube radio at full song with power to spare. Need more output? One regulator can feed many complementary transistors for amps aplenty.

For simplicity's sake we haven't used the technically correct terms for transistor connection legs but they're sort of required to explain the complementary transistor's operation. The correct term for a transistor's input is the collector. The correct term for the transistor's output is the emitter. Transistors have what's called a base leg, only until now we referred to them as ground or adjust.

These base legs serve as a sort of reference for the regulator, only instead of referencing ground, the base leg in a complementary transistor references the voltage output of the regulator's emitter (output). In other words, instead of driving a device directly with its emitter (output) leg, the regulator drives the base leg of the complementary transistor.

Complementary transistors can mount as close to or as far away from the regulator. That's a good thing as these transistors usually require fairly big heat sinks; their capacity means they can generate lots of heat if asked to drive great current loads (fans and radios, for example). So long as their collectors (inputs) connect to the battery (preferably through an ignition switch), their emitters (outputs) connect to the devices, and their bases connect to the regulator's outputs (emitters), these complementary transistors can operate just about anywhere in a vehicle.

The only potential issue with complementary transistors is that they don't reproduce the regulator's output exactly; they "eat" about 0.7 V. So if you connect a 6V regulator to a complementary transistor, it will emit 5.3 V.

If using an adjustable regulator, tune it to emit roughly 0.7 or more additional V. But remember that we said that you can't alter a fixed-voltage regulator's output? Well we lied; resistance in a fixed regulator's base connection (ground) will fool it into increasing its voltage output. A diode usually reduces output by 0.7 V, so routing a fixed regulator's ground through one will increase its output by the same amount. Slick, eh?

Common Resistor Values And Regulator Voltages
The formula to calculate resistor values to achieve a particular voltage is easy:
V = 1.25(1 + [R2 ÷ R1])

That said, not everybody wants to go through the motions. The following values will get you close; however, with one exception, you'll have to calculate your own values to offset the voltage loss when using a complementary resistor:

R1 R2 Voltage Application
1,000 82 1.35 Sun tachometer sending unit power
1,000 680 2.1 Most red, orange, yellow, and green LEDs
820 1,500 3.53 Most blue and white LEDs (but verify first)
330 1,000 5.03 USB-powered electronics (MP3 players, phones, etc.)
1,200 4,700 6.15 6V components (gauges, fans, and radios)
220 1,000 6.9 6V components when using a complementary transistor