Wiring Schematic Diagram

Here is a circuits light a 12V/20 watt lamp when the contacts are touched and the skin resistance is about 2 Megs or less. This circuit uses a power MOSFET (IRF510) which turns on when the voltage between the source and gate is around 6 volts. The gate of the MOSFET draws no current so the voltage on the gate will be half the supply voltage or 6 volts when the resistance across the touch contacts is equal to the fixed resistance (2 Megs) between the source and gate.

Drain to Source Voltage        : 100 V
Drain to Gate Voltage          : 100 V
Continuous Drain Current (ID)  : 5.6 A
Pulsed Drain Current (IDM)     : 20 A
Gate to Source Voltage (VGS)   : ±20 V
Maximum Power Dissipation (PD) : 43 W