Join Date: Sep 2000
Location: Shrewsbury, MA, USA
It looks like a high voltage switching transistor, and a relay operated reed switch. The switching transistor is connected across the fixed resistor on the back of the fuel guage. As the resistance of the sender circuit decreases (going towards empty)the amount of current in the circuit which increases the voltage drop across the fixed resistor. When the voltage drop gets to the switching transistors setpoint the output of the transistor picks up the coil for the reed switch closing the reed switch. The reed switch provides the output to the Fuel light throough the yellow wire.
The red wire provides 12V to the circuit to operate the relay and provide power out the yellow wire to the light. It probably also provides a reference voltage to the switching transistor. The green wire is the signal wire to the switching transistor, black is ground.
The yellow wire should be attached to the reed switch contact, as should the Red wire, although it may do this through the circuit board.
Switching transistor circuits like this do use either or both resistors and diodes.
What color wire attaches to the piece that is melted, Red, Green, Black or yellow.
1969 Indy Pace Car
350/300HP RPO Z11