Usage:
The 1P3550 Wiring Harness Tester Group can be used for troubleshooting any 24 volt electrical circuit, but, its primary use is for a test of the electrical circuits for transmissions in Caterpillar Off-Highway trucks and tandem-powered scrapers. To use the 1P3550 Tester to check machines, see the Service Manual. Test results of voltage or lamp readings must be the same as the specifications given in the Service Manual.
The illustration on page two is a schematic of the 1P3550 Wiring Harness Tester. Tests that can be made with this tester are as follows: 1- Battery Voltage Test; 2a- Circuit Activity (voltage presence) test by use of lamps; 2b- Circuit Voltage Test by Use of Meter; 3a- Circuit Continuity Test - Ground Seeking; 3b- Circuit Continuity Test - Short Seeking; 4- Solenoid Test.
Before each test, turn all switches to the OFF position. If the machine has a RUN/NEUTRAL switch, it must be in the RUN position, and the machine disconnect switch must be in the ON position.
NOTE: Do not operate the engine while tests are made. If there is a power failure in the electrical system, be sure to first check the fuses and circuit breakers of the machine.
Battery Voltage Test
1 Always test the battery first, during troubleshooting of an electrical system. A test of the battery will give an indication of the amount of charge in the battery (or batteries).
2 Connect 1P2857 and 1P2858 Battery Lead Wires (1) to the terminals of meter (2) and batteries (3). With no load, an analysis can be made of the meter reading, for batteries connected in series for a 24V system. See the chart that follows.
3 If the battery charge is low, the battery must be charged.
4 If the battery charge is low, a more thorough check must be made. Use either the 5P957 or 5P3514 Coolant and Battery Fluid Tester to check the specific gravity of the electrolyte in each battery cell. Use the findings of both the no- load test and the specific gravity test to get battery condition, according to the chart that follows.
Circuit Activity (Voltage Presence) Test - Using Lamps
The test most used to check an electrical system for normal operation, is the circuit activity test, where the lamps of the tester are used to show active circuits. When the test connections are made according to the procedure that follows, the test circuit will give a parallel circuit to the machine frame, through the lamps of the tester. When a test lamp lights (comes on), the serviceman knows there is voltage at that point in the machine electrical circuit to which the tester has been connected.
NOTE: The tester lamps are for use with a 24 volt system and, if outside light is bright or if the electrical system has 10 volts or less, it is possible that the test lamp will not be bright enough to be seen.
1 Use the correct battery lead wire to connect the meter ground (-) terminal to a good ground on the machine frame. Use the correct test harness to connect the machine wiring harness test point to the connector on the tester. Put the GROUND SWITCH in the ON position. As the machine circuits are activated, one or more lamps on the tester will light. When a lamp lights (comes on), it is an indication of voltage at the "test point".
Circuit Voltage Test By Use Of Meter
1 Use this test to find the voltage present at a specific test point on the machine. Use the correct battery lead wire to connect the meter ground (-) terminal to a good ground on the machine frame. Use the correct test harness to connect the machine wiring harness test point to the connector on the tester.
2 Turn the selector switch and read the circuit voltage on the meter.
NOTE: The ground switch (lamp control) can be either ON or OFF for this test. If the ground switch is ON, the lamps connected to the active circuits will light.
NOTE: Resistance in an electrical circuit (caused by wire size and/or length, connectors and/or corrosion) will decrease current (voltage) flow. The meaning of this is, that the farther away from the machine power source (batteries) a test is made, the smaller the voltage reading will be on the meter.
On many machines there is a minimum amount of voltage that is needed to activate some of the components in the electrical system. As an example, the shift synchronizing solenoids used on Caterpillar off-highway trucks and tandem-powered tractor-scrapers will not activate with less than 20 VDC. This test can be used to find the cause of an electrical circuit problem if a solenoid that is known to be good will not operate because there is too much voltage loss in the circuit that controls the solenoid.
Harness Continuity Test
1 In a test of a harness for continuity, both ends of the harness are disconnected. A ground adapter is connected to one end of the harness. The ground adapter comes to all of the wires in the harness to machine ground. Connect the tester harness to the transmission harness and connect the ground adapter to the other end of the transmission harness and to machine ground. Connect the positive (+) terminal of the tester to the machine power source (+24V). Turn the power switch to the external position and turn the ground switch OFF. Turn the selector switch through all positions.
2 With the 1S9532 Jumper Cable removed from the battery and harness jumper terminals, current must go through the battery power lamp. The battery power lamp will be ON in each position of the selector switch if the harness wire for that position of the switch makes contact through the harness to machine ground at the other end.
NOTE: Failure to remove the 1S9532 Jumper will cause the fuse in the 1P3550 to burn out since there would be no load to prevent current flow from being too high.
Circuit Continuity Test - Ground Seeking
A typical electrical circuit problem can be a damaged or broken wiring harness. This type of problem can cause a short circuit between the wiring harness and the machine frame. This will normally burn out a fuse or cause a circuit breaker to open. To find the source of this type of problem, test each component in the circuit according to the procedure that follows.
1 Connect the tester harness to the transmission harness and connect the positive (+) terminal of the tester to machine voltage (+24V).
NOTE: The other end of the transmission harness must be disconnected. Put the power switch in the extermal position and the ground switch OFF. Turn the selector switch through all the positions.
NOTE: The 1S9532 Jumper Cable must be removed from the battery and harness jumper terminals for this test. Failure to do this will cause the fuse in the 1P3550 to burn out if there is a short circuit in the harness.
2 If the battery power light comes on for any position of the selector switch, the harness wire for that position of the selector switch is grounded. The schematic for a test of a harness for grounds shows the harness with the wire to connection "P" grounded. When the selector switch is moved to position "P", current is sent through the power light and through wire "P" to ground.
Circuit Continuity Test - Short Seeking
The short seeking circuit continuity test can be used to check for an internal (inside) short in a wiring harness, or to check for continuity in a switch. To check a component for internal continuity, use the procedure that follows.
1 Connect the positive (+) lead wire to the machine power source (+ 24V) and connect the negative (-) lead wire to a good ground on the frame of the machine. Connect both wires to the meter terminals. Install 1S9532 Jumper Wire (1) so that the current goes around the battery power lamp.
2 Disconnect the component, or the part of the machine electrical circuit that is to be tested, from the machine electrical circuit. Connect the correct test harness to the connector on the tester, and connect one of the loose end connections of the test harness to the component, or the part of the circuit that is to be tested.
3 Turn the ground switch OFF and turn the selector switch; as the selector switch is turned to each position, a light will come on for that position. If a light other than the light for the position of the selector switch comes on, it is an indication of continuity between those circuits. Check the Service Manual to see if this continuity is an indication of an internal short between wires.
Solenoid Test
In the test of a solenoid, the tester sends current to activate the solenoid when the solenoid test switch is pushed. The resistance in the solenoid test circuit decreases the voltage that goes to the solenoid to the minimum voltage that is necessary to activate the solenoid. This test will show not only a completely bad solenoid that will not activate at all, but also a solenoid that could activate if the system voltage were correct but would not activate if the system voltage were low.
Tester Group Check
1 Connect battery lead wires (1) from the plus (+) and minus (-) binding posts to a 24 volt battery.
| NOTICE |
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Always connect leads to the tester before connecting to the battery. |
2 Turn the power switch to EXTERNAL and the ground switch to OFF, then read the battery voltage on the meter.
3 Turn the ground switch to ON and turn the rotary switch through all letter positions. The battery power bulb will go on and each bulb will go on according to the letter of the rotary switch selection.
4 If the continuity bulbs do not go on and a voltage does not show on the meter, install a new fuse (2).
5 If the continuity bulbs do not go on and a good voltage shows on the meter, put the jumper wire across the battery power bulb.
6 If the continuity bulbs go on with this jumper, install a new battery power bulb, and do step 3 again.
7 Disconnect the tester from the 24 volt battery and fasten the 16-pin plug adapter (ground) cable (3) into the 16-pin plug.
8 Push the continuity light probe into each letter socket of the tester connector and put the clip of the light in contact with the same letter prong of the receptacle. Each complete circuit will cause the bulb to go on.
NOTE: The test harness of the 1P3550 Wiring Harness Tester is permanently connected to the tester. For this reason, any time there was damage to the test harness, it was necessary to send the complete tester group to Sun Electric Corp. for repair. With the conversion procedure given in Special Instruction Form SMHS7424, the wiring harness can be disconnected from the tester, for easy replacement of a damaged harness assembly. Any of the test harnesses from the 5P6590 Wiring Harness Tester can be used with the 1P3550 Wiring Harness Tester after conversion. This also increases the range of tests that can be made with the tester.