Test Lights; 12 Volt Test Light - Chevrolet Trailblazer Service Manual

Jumper wires are simple, yet extremely valuable, pieces of test equipment. They are
basically test wires which are used to bypass sections of a circuit. Although jumper wires
can be purchased, they are usually fabricated from lengths of standard automotive wire
and whatever type of connector (alligator clip, spade connector or pin connector) that is
required for the particular application being tested. In cramped, hard-to-reach areas, it is
advisable to have insulated boots over the jumper wire terminals in order to prevent
accidental grounding. It is also advisable to include a standard automotive fuse in any
jumper wire. This is commonly referred to as a "fused jumper". By inserting an in-line fuse
holder between a set of test leads, a fused jumper wire can be used for bypassing open
circuits. Use a 5 amp fuse to provide protection against voltage spikes.
Jumper wires are used primarily to locate open electrical circuits, on either the ground (–)
side of the circuit or on the power (+) side. If an electrical component fails to operate,
connect the jumper wire between the component and a good ground. If the component
operates only with the jumper installed, the ground circuit is open. If the ground circuit is
good, but the component does not operate, the circuit between the power feed and
component may be open. By moving the jumper wire successively back from the
component toward the power source, you can isolate the area of the circuit where the
open is located. When the component stops functioning, or the power is cut off, the open is
in the segment of wire between the jumper and the point previously tested.
You can sometimes connect the jumper wire directly from the battery to the "hot" terminal
of the component, but first make sure the component uses 12 volts in operation. Some
electrical components, such as fuel injectors or sensors, are designed to operate on about
4 to 5 volts, and running 12 volts directly to these components will cause damage.

Test Lights

12 volt test light