Testing For "Shorts" In the Circuit

Measuring Voltage Drop-Accumulated Method:

To simplify the discussion of shorts in the system please refer to the schematic.

Resistance check method
1. Disconnect the battery negative cable and remove the blown fuse.
2. Disconnect all loads (SW1 open, relay disconnected and solenoid disconnected) powered through the fuse.
3. Connect one probe of the ohmmeter to the load side of the fuse terminal. Connect the other probe to a known good ground.
4. With SW1 open, check for continuity.
continuity; short is between fuse terminal and SW1 (point A).
no continuity; short is further down the circuit than SW1.
5. Close SW1 and disconnect the relay. Put probes at the load side of fuse terminal and a known good ground. Then, check for continuity.
continuity; short is between SW1 and the relay (point B).
no continuity; short is further down the circuit than the relay.
6. Close SW1 and jump the relay contacts with jumper wire. Put probes at the load side of fuse terminal and a known good ground. Then, check for continuity.
continuity; short is between relay and solenoid (point C).
no continuity; check solenoid, retrace steps.

Voltage check method
1. Remove the blown fuse and disconnect all loads (i.e. SW1 open, relay disconnected and solenoid disconnected) powered through the fuse.
2. Turn the ignition key to the ON or START position. Verify battery voltage at the B+ side of the fuse terminal (one lead on the B + terminal side of the fuse block and one lead on a known good ground).
3. With SW1 open and the Digital Multimeter (DMM) leads across both fuse terminals, check for voltage.
voltage; short is between fuse block and SW1 (point A). no voltage; short is further down the circuit than SW1.
4. With SW1 closed, relay and solenoid disconnected and the DMM leads across both fuse terminals,
check for voltage. Voltage short is between SW1 and the relay (point B).
no voltage; short is further down the circuit than the relay.
5. With SW1 closed, relay contacts jumped with fused jumper wire check for voltage. Voltage short is down the circuit of the relay or between the relay and the disconnected solenoid (point C).
no voltage retrace steps and check power to fuse block.