Was most likely my blue gauge, as I posted up about the temps I had seen once using it.
They sell for anything up to £40 on the bay, but sometimes as low as £15-£20.
If you only want it to measure a single temp it can be done for around £4, I measure air filter and plenum, adding a switch is only a few quid extra.
They are(if it's the ones you're reffering to) 5V, so a 2 p resistor later work perfect on 12V, I make them safe up to 15 just to be on the safe side.
If you pm me your email, I'll send you some piccies, I have an account where I get mine, so could get you one add a resistor, and extend the wire for sensor as is very short as supplied for computers, comes to about £6-£7.
tabetha