Here is what you need:

 

1) T-1 3/4 super bright LED

1) 1200 ohm 1/2 Watt resistor

A few feet of 22 AWG wire

some heat shrink tubing

 

Solder about 3' of wire onto the Cathode of the LED. This is the ground wire.

Solder 4-6' of wire to the Anode of the LED.

Solder the resistor to the end of the long wire.

Leave the other lead of the resistor about an inch long.

 

To use the tester:

 

Tape the LED on the dashboard where you can see it.

Run & tape the wires so they don't get in the way of operating the car.

Connect the ground wire to any convienient grounded fastener.

The resistor lead is a good size to sneak into most of the connetors on an EA82 & older Subaru. It works on the ECU connectors and the ones with 1/4" flat tabs.

 

I have used this to figure out numerous electrical problems over the years.

 

Intermitant no crank - Start by slipping the resistor into the signal connector on the back of the starter. If the LED lights when you turn the key, you know that everything from the connector back is good. If it doesn't move it to another of the 3 or so in the harnes back towords the key switch.

 

I used it to monitor the EGR valve computer signal a while back. If I remeber correctly, the EGR solinoid is activated until the engine reaches normal operating temperature. This disables the EGR valve while the engine is cold.

 

The LED is great for these intermittant troubles, because you can leave it connected, and check the function every time you use the car.

cool, good tip on using the resistor prong as a probe.