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Tech Corner

Diagnosing Car Starting Problems – submitted by Rich Weiss
Based of Google searches

This month’s article is about the frustrating problem of a car that won’t start. We turn the ignition key to the start position,
and hear nothing, or perhaps a click, but the starter motor is not activated. In this case, where the engine doesn’t crank, we
can eliminate mechanical issues with the ignition system or a fuel problem.

Problems with the starting system can almost always be traced to one of five sources: the battery, the starter switch, the
starter relay, the starter solenoid or the starter motor itself. Checking the battery is straightforward and a pair of jumper
wires can usually eliminate this as the cause. The article will focus on the remaining four sources, in turn. The ignition
switch has a hot wire, directly connected to the battery, when turned to the start position, routes current to the starter
solenoid. As we will soon in the wire diagrams, sometimes there is a starter relay, that opens a circuit and is also activated
by the ignition switch.

Ignition Switch

Problems with the ignition switch can result in a no-start situation (starter motor fails to turn) or the starter motor may fail
to stop when the key is released from the start position. This may be because the contacts in the switch have been worn or
burned. To test for this, use a test light in contact with the solenoid start terminal or starter relay, if there is one. A good
ignition switch will cause the test light to light up when the key is turned to "Start." If the test light does not light up, there
is either an open wire in the circuit or the switch is defective.

1973-1976 TR6

Other symptoms of a defective switch are problems with accessories, so if, for example the radio fails to operate, more
than likely the switch needs to be replaced. If the ignition switch is ok, we can move on.

Starter Relay

In those cases where a starter relay is present, the failure of a test light when the solenoid starter terminal is tested, could
indicate problems with the relay. A starter relay acts as an electrical circuit completer or circuit breaker in between the
vehicle's battery and the starter motor. It helps to boost the battery's current so that not as great a current is required at
ignition. The starter relay is sometimes, but not always, used in addition to a starter solenoid.