Does this make any sense and could someone make it up for me for a price?

 

The RangeRover has six individual wires from the glowplug controller, one to each plug.

Inside the controller each wire connects via a low value resistor to the relay which supplies them with 12V. The controller monitors the voltage drop accross these resistors and therefore detects a fault when one (or more) plugs fail (and therefore the current through the relevant resistor is zero) and flags this as a fault code.

 

You could do something similar I guess. Not a five minute solution but I reckon that it would work to drive LEDs exactly as you want.

 

Something like a 0.05 ohm high power resistor in series with each plug all being powered from a common relay, and an op-amp monitoring the voltage drop across each resistor and driving an LED would almost certainly work.

 

At 10A per plug, the power in each 0.05ohm resistor is only 10X10X0.05 = 5Watts so a fairly small wirewound resistor should do. Voltage drop would be 10X0.05 = 0.5Volts so not likely to affect the performance of the plugs and is plenty for a basic amplifier circuit to detect and drive an LED.

 

Going lower, say 0.01ohm would be 1 watt dissipation and 0.1 volts dropped so even less impact and should still easily drive an op-amp.

I have emailed someone for u will let you know what he says.

cheers David :)