There are electronics groups better suited to discuss your need.
But here's a thought, any way.

A current sense is often provided by a low value series resistor on
the + rail across the base/emitter junction of a transistor which
turns on when the voltage drop exceeds about 0.6 volts
A collector resistor limits the output current to about 10 milliamps
and activates a LED connected to the - rail when active.

This is a low count solution, but probably not best suited
to your purpose, because it drops a volt and wastes some power.

You might consider a VERY low value series resistor - i.e. the voltage
drop across a length of the positive rail cable feeding the two inputs
of an op amp, whose output feeds a dropper resistor of 1.2Kohms say,
to a LED on the negative rail.

The adjustability is provided by a 25Kohm pot connected to the op amp
output at one end, whose wiper connects to the + op amp input though
a 200 ohm resistor, and the other end of the pot connects to the most
positive end of the + rail .
The - input of the op amp connects to the least positive end of the
positive rail through a 200 ohm resistor.

Not just any op amp will do for this: the key is an op amp type that
does NOT latch on an input as high as the + rail.

Brian Whatcott Altus OK

On 24 Feb 2004 11:48:17 -0800, (Norm Freedman)
wrote:

Any electronics experts out there? Would appreciate help with a simple
circuit:

to light an LED when current in a 12vdc circuit goes above
approximately 10 amps (adjustable from about 8 - 13 amps would be
nice) and drop out when current goes below that set point. Maximum
current is about 20 amps.

Any ideas?

Thanks for the help