Testing the Chrysler Starting System, 1960 - 1980s RWD
Very little needs to be tested with this starter. There is no accessible test point after the solenoid contact disc. Troubleshooting is limited to measuring voltages on the two terminals and the amount of current drawn during cranking. As a starting point, review the General Theory of Operation for starters.
Many clues to a starting problem go unnoticed but they can speed up the diagnosis process. These clues include:
1. Did the problem occur suddenly and without warning or has the starter been cranking the engine slower and slower over time?
2. Is the problem intermittent? Will the starter work normally sometimes and not at others?
3. What happens to the brightness of the head lights or dome light when the problem occurs?
4. What sounds do you hear? A single rather loud clunk each time you turn the ignition switch to "crank"? A single, barely audible click from under the hood? A loud ratcheting or harsh buzzing sound?
High Current Circuit
The high current circuit just contains the battery, cables, solenoid contacts, and starter motor. Begin with a visual inspection of the cables. In particular, look for broken strands and corrosion next to the starter terminal and the ground terminal on the engine block, and next to both cable clamps. If the cable clamps are breaking apart and can't be tightened, or if many of the copper strands of wire are broken off, the cable should be replaced. Universal cable clamps bolt onto the end of the cable after it has been cleaned up with sandpaper but they are really meant to be a temporary repair. They are not meant to be a permanent fix even though that's what happens most of the time.
Problems in this circuit result in slow cranking, a loud, rapid, repeated clicking sound, and a single loud clunk with no cranking. All of these things can be caused by excessive resistance in the circuit. The problem is that undesirable resistance can be much too small to measure, but we can see the results of it in the form of a voltage drop. Excessive resistance causes a decrease in the amount of current flow to the starter. That also leads to very little drop in battery voltage during cranking. Worn bushings in the starter will cause it to drag and slow down resulting in less generated back EMF and greatly increased current flow from the battery. That higher current flow will draw down the battery voltage during cranking more than normal. See the section on Battery Testing for a description of internal resistance.
The secret to determining if slow cranking is caused by a starter that is drawing excessive current or by undesirable resistance in the circuit that is causing too little current flow is by measuring the actual current. A professional will use a starting system tester to do that. For this gear reduction Chrysler starter, 150 amps is typical when cranking a small V-8 engine. When you don't have a starting system tester, you'll need to interpret various voltmeter readings. Start with a fully charged battery. See Basics of Batteries for more details. During cranking, the battery voltage will drop from the normal 12.6 volts but it must not drop lower than 9.6 volts. Measure the voltage right on the battery posts, (not the cable clamps), while a helper cranks the engine. If the voltage remains relatively high, in the area of 10.5 - 11.5 volts, suspect high resistance in the circuit. Refer to Voltage Drop Tests in a High Current Circuit. Next, measure the voltage during cranking with one meter probe on the engine block and the other probe right on the large battery terminal on the starter, (not the cable end). The voltage measured there must be very nearly the same as that measured in the previous step. If you find a difference of roughly half a volt or more, follow the steps in Voltage Drop Tests in a High Current Circuit to locate that resistance.
Another clue that there is excessive resistance in the circuit can be found by watching the head lights. They are on a different circuit so they will remain bright when that excessive resistance causes low voltage at the starter. The only things the lights and starter have in common are the battery and cable connections, so if the lights dim during cranking, your diagnosis is done. Clean and tighten the battery cables or replace the battery.
Finally, slow or no cranking due to excessive resistance can be caused by worn contacts in the solenoid. That is the only place that is inaccessible for taking voltage measurements. Most of the time this results in no cranking at all, and one loud clunk from the starter each time the ignition switch is turned to "crank". Voltage at the starter will remain high since no current is flowing in the high current circuit.
That all-too-common rapid ratcheting sound is usually another indication of excessive resistance in one of the battery cable connections. Once the solenoid engages, the very high starter current causes a big voltage drop across the bad connection. The drop in voltage to the solenoid is so great that it can't stay engaged against the return spring pressure. When it retracts, the high current circuit turns off and the voltage goes back up. With the higher voltage, the solenoid engages again. This repeats over and over very quickly causing that rough buzzing sound.
One final problem that can be very hard to diagnose is one worn brush. That creates an open circuit for one of the two pairs of field coils. With only one of the two circuits working, current flow in the high current circuit will be half of normal. The motor will spin very slowly so little back EMF is generated. With low back EMF, current flow to the starter goes up almost to the normal 150 amps. The normal current flow is misleading. This is one time when you'll need to replace the starter to verify the cause of the slow cranking.
In the previous section, the solenoid engaged and could be heard. That proved the small current and medium current circuits were working. When you do not hear the solenoid engage, most problems will be found in the small current circuit. If that circuit is working, you will hear the light click of the starter relay. Test for voltage on the smaller solenoid terminal on the starter. If it is there when the ignition switch is in the "crank" position, one or both of the solenoid coils is open. Sometimes the hold-in coil working alone is strong enough to engage the solenoid by itself. A valuable clue is the starter may work when a battery charger is being used to raise battery voltage. The most likely cause of an open solenoid coil is a loose nut on the small bolt that lets it spin. The two coil wires are soldered onto the head of that bolt inside the housing. One or both of the those wires can break off when that bolt turns when you're trying to attach the brown solenoid wire.
If you use a jumper wire to apply battery voltage to the solenoid terminal and there is no spark, both wires inside are broken off the terminal. If there is a spark but the solenoid doesn't engage, suspect one wire is broken off. You can do this test by using a screwdriver blade to touch the starter and solenoid terminals together right at the starter. When this quick test causes the starter to crank the engine but no voltage comes from the starter relay, listen for the relay to click. If it does, you'll need to diagnose the break in the medium current circuit. See Quick Tests at the Relay for more on this topic.
Problems in the Low Current Circuit
When you don't hear the relay click, there are three possibilities. The battery voltage feed to the relay could be missing, the ground circuit could be open, or the relay coil could be open. You can quickly verify the medium and high current circuits are working by jumping the fat red and brown wires at the relay socket. Use a substantial jumper wire to prevent burning your fingers. You'll be switching up to 20 amps. The most common problem in the small current circuit is a defective neutral safety switch in the ground circuit for the relay. Resistance measurements at the relay socket will identify the circuit with the problem and are described next.
Quick Tests at the Relay
The starter relay socket is a convenient place to split the small and medium current circuits into four parts. Four measurements will identify which one has the problem. The tests can be done with a voltmeter or a test light.
Begin with the small diameter yellow wire. It must have full battery voltage when the ignition switch is in the "crank" position. If it is missing, troubleshoot the ignition switch circuit. The larger diameter red wire must have full battery voltage at all times. If it is missing, suspect that wire is broken off the positive battery cable.
For the last two wires you'll be testing for a complete circuit to ground. You can do that with an ohm meter or with your test light's clip lead connected to the battery positive post. The light will turn on when you probe a ground connection. You should find low resistance to ground on the large brown wire and the small black wire. The brown wire reads to ground through the two solenoid coils in the starter. The black wire reads to ground through the neutral safety switch. Troubleshoot any of those circuits that do not measure correctly.