Symptom Related Diagnostic Procedures

When trouble develops in the starter motor circuit, and the starter cranks the engine slowly or not at all, several preliminary checks can be made to determine whether the trouble lies in the battery, in the starter, in the wiring between them, or elsewhere. Many conditions besides defects in the starter itself can result in poor cranking performance.
To make a quick check of the starter system, turn on the headlights. They should burn with normal brilliance. If they do not, the battery may be run down.
If the battery is in a charged condition so that lights burn brightly, operate the starter motor. Any one of three things will happen to the lights: (1) They will go out, (2) dim considerably or (3) stay bright without any cranking action taking place.

If Lights Go Out
If the lights go out as the starter switch is closed, it indicates that there is a poor connection between the battery and starter motor. This poor connection will most often be found at the battery terminals. Correction is made by removing the cable clamps from the terminals, cleaning the terminals and clamps, replacing the clamps and tightening them securely. A coating of corrosion inhibitor (petroleum jelly will do) may be applied to the clamps and terminals to retard the formation of corrosion.

If Lights Dim
If the lights dim considerably as the starter switch is closed and the starter operates slowly or not at all, the battery may be run down, or there may be some mechanical condition in the engine or starter motor that is throwing a heavy burden on the starter motor. This imposes a high discharge rate on the battery which causes noticeable dimming of the lights.
Check the battery state of charge. If it is charged, the trouble probably lies in either the engine or starter motor itself. In the engine, tight bearings or pistons or heavy oil place an added burden on the starter motor. Low temperatures also hamper starter motor performance since it thickens engine oil and makes the engine considerably harder to crank and start. Also, a battery is less efficient at low temperatures.
In the starter motor, a bent armature, loose pole shoe screws or worn bearings, any of which may allow the armature to drag, will reduce cranking performance and increase current draw.
In addition, more serious internal damage is sometimes found. Thrown armature windings or commutator bars, which sometimes occur on over-running clutch drive starter motors, are usually caused by excessive overrunning after starter. This is the result of such conditions as the driver keeping the starter switch closed too long after the engine has started, the driver opening the throttle too wide in starting, or improper carburetor fast idle adjustment. Any of these subject the over-running clutch to extra strain so it tends to seize, spinning the armature at high speed with resulting armature damage.
Another cause may be engine backfire during cranking which may result, among other things, from ignition timing being too far advanced.
To avoid such failures, the driver should pause a few seconds after a false start to make sure the engine has come completely to rest before another start is attempted. In addition, the ignition timing should be checked if engine backfiring has caused the trouble.

Lights Stay Bright; No Cranking Action
This condition indicates an open circuit at some point, either in the starter itself, the starter switch or control circuit. The solenoid control circuit can be eliminated momentarily by placing a heavy jumper lead across the solenoid main terminals to see if the starter will operate. This connects the starter directly to the battery and, if it operates, it indicates that the control circuit is not functioning normally. The wiring and control units must be checked to locate the trouble.
If the starter does not operate with the jumper attached, it will probably have to be removed from the engine so it can be examined in detail.