Electronic – Light an LED when load is in circuit

Longish comment:

The circuit in the first schematic won't work: none of the transistor pins is connected to a supply, so it will just connect the capacitors together, but without any appreciable effect. Also, with one wire only you are not picking any signal.

Also, instead of randomly pick wires from the speaker, if you have a multimeter you'd better measure the signals (set for AC) to understand where you get the signal; and connect the ground of the speaker to the ground of your circuit, otherwise you'll pick up only noise.

In the circuit you hooked up, the collector seems to be connected to the supply (+5), but it's quite hard to read: could you make a schematic of your connection? There are several tools available, but if you use Falstad, you can also try to simulate it and have an idea about if it can work.

Update:

Neither this circuit is likely to work: you have a too small drop over the base-emitter junction of the transistor. The most common configuration is the common emitter, where you place the speaker (eventually with a resistance to provide the right biasing current) to the base-emitter junction of the transistor, and then the LED with a limiting resistor between the 5V supply and the collector.

Something like this may work:

You have to set the right base resistor depending on the voltage of the speaker and the sensitivity that you want for the blinker. You may also use a potentiometer, to set it dinamically, but be sure to check the maximum ratings for the transistor.

As described, you could place a resistor from CHG to either battery+ or to Vin and an LED from CHG to ground. Resistor value depends on desired LED current.

When CHG is low LED is off.
When CHG goes O/C CHG is pulled high by R and LED is driven.

If you use say Vin = 16 V and want say 2 mA I_LED the R ~~= ( Vin - V_LED)/I_LED
~= (16-2) / .002 =~~ 6k8.

The LTM8062 comes in an LGA package which is liable not to be overly home-constructor friendly.

It costs about $17 in 1's which is high if only basic functionality is going to be used.

However, it will work with a range of battery chemistries and it has MPPT capability. If you need the fancier features it's a bargain.

LTM8062 data sheet here.

15 x 9mm LGA package.