Sorry, the heater bit was more of a joke, if you run 12V through the temp sensor which I think is a (thermocouple) you would make the sensor a heater, and because of the size of the cables, you would see a voltage drop.
Probably best to run the voltage sensor from the battery, the two in the centre. Powering the gauges (the four on either side) should be ok, from the clock, and thats what I plan to do anyway.
Technically, volt gauges should be powered from a separate source from whats being measured.
Had a look at the boost gauge today, worked out the power side with the 4 wires, and colours. Getting the boost gauge to read pressure threw me. I'm guessing that the black pressure "receiver" (it has 3 wires) needs to also have 12v to run the electronics in it (which would be the red and black wires), and the white would connect to the red wire on the 2 wire input to the back of the gauge. The remaining of the two sensor wires (black) then would need to go to the car body/battery negative? Is that right? I would hate to let the magic smoke out.
With the temp gauge, (ignoring the voltage issue) if its a thermocouple, then its important to get the polarity around the right way for the gauge to read correctly, (it won't let smoke out if its connected round the wrong way) if its an RTD, then it won't matter, I'll check this tomorrow using our gear there.
Tim