I have fitted a set of "Autotecnica" 52mm gauges with an M:SPEC dash pod (made by Autotecnica)
The Volt Gauge is a simple 2 wire (+ & -) connection to a switched power source of your choosing & reads voltages to the first decimal point i.e 12.4v.
The Oil Temp Gauge has 3 wires, the same + & - and a sense wire to the sender unit that is supplied with the gauge. I am using it to monitor transmission temp but it can also monitor engine oil temp's. The gauge does not read temps under 50°C and goes up in 1° increments.
The positive's
Changeable colour readout to match dash lights & appear quite accurate when compared to multi metre & laser thermometer.
The Negative
Can't be dimmed, some colours are too bright for night viewing (red is best imo)
Pod is paintable & is secured down with adhesive (I used windscreen sealant as it is non corrosive & is easily cleaned up).
Gauges were purchased from Repco, $50 for volt & $90 for temp & pod from SuperCheapAuto for $25.
http://www.autotecnica.com.au/