It all depends on the current/wattage rating on the indicator lamp. Let's assume it's rated for 1Watt (you'll have to change the calculations based on this value).
That means that for 12V drop through the lamp, it will have I=P/V=1W/12V=0.083A=83mA going through it. Obviously, this means that the lamp's resistance will be R=V/I=12V/0.083A=144Ohm.
Through elementary voltage division principles, Vj=(Rj/Req)*Vsource. With Vj the output voltage, Vsource the input voltage, Rj the load resistance and Req the total resistance of the circuit. In our case, Vj=12V, Rj=144Ohm, Req=R+144Ohm (with R the unknown resistance and since voltage division works for SERIES circuits with the lamp and resistor in series) and Vsource=125V. If we calculate for R, we get R=1356Ohm=1.356kOhm.
The closest value to this would probably be 1.47kOhm since we want to round upwards to not overload the lamp.
The power going through the resistor will be P=V^2/R=(125-12)^2/1470=8.68Watt.
Of course, this value for R will only work for the current lamp and would have to be recalculated for every other lamp value.
Edit: I agree with W1zzard, you should know what you're doing before tackling heavy current circuits...