monitor

Been looking at the NASA BM1 Battery Monitor as I am a bit of a statistics and analytical anorak and like to know what is going in behind the scene :D But at over £100 for a BM1 it does seem a little pricey to say the least! So I located an alternative Battery Monitor for under £20 T: but can a...

Ok, ordered 2 monitors and a switch.. Now wiring, on a pre 96 T4 - any one have a step by step... The monitors have a black and red - so simple, + & - The switch has 3 pins - +,- and earth for the LED on that.. But what cable can I spice into which is behind dash - near ash tray - I know...