We are all enemies of father time. As a service technician, the ticking of a clock represents the ever-present threat of flat rate, and the ability to make money for yourself, and your company. Day-in and day-out, the clock keeps ticking away, making what you do every day a real challenge.
While there's no way to stop the clock, or even bias it to your advantage, you can strike back at its relentless nature by employing some tricks of the trade in the things you do. By using these tips, you may actually come out ahead in your battle against the clock.
A Shortcut To Shorts
Here's a trick for tracking down an electrical short. First, connect a 5-amp circuit breaker across the fuse block terminals of the affected circuit. With the circuit activated, probe the various parts of the circuit and connectors with your test light. If the light blinks on and off, continue on to the next portion of the circuit. When you get to a point where the test light doesn't come on, the short will be between that point and the last point where the light flashed.
Unlocking Defroster Woes
Ever wonder if there's a quick way to test the rear-window defroster? There is. Just turn on the defroster switch and connect your trusty test light.
To check the power supply, connect the clip end of the test light to one end of the grid buss bar and touch the other buss bar with the probe end. If the light comes on, power and ground are good. If the light doesn't come on, connect the ground clip to another ground. If the light comes on now, there's an open ground circuit. If the light still doesn't come on, check the fuse and connections.
To check the defroster's heating ability, connect the clip end of the test light to a good ground. Now, touch each horizontal bar at the supply end with the probe. The test light should glow brightly. Continue moving across the bar to the ground end and touch the bar gain. If the bar is working correctly, the light should dim as you move towards the ground end.
If the test light brightness stays the same as you move across the bar, you've found one with an open circuit. Repair kits are available commercially.
Did you know that a faulty alternator can cause onboard electronics to go haywire? The fact is, AC current leakage from the alternator can confuse electronic controllers, so it's a good idea to check for too much current when chasing weird, ghost-like problems.
One way to test for this is by connecting a digital voltmeter to the battery, with the engine running. With the meter set to the AC range on the millivolts scale, you should see no more than 400 millivolts AC. Repair/replace the alternator as necessary.
Wondering whether a key-off current drain is killing the battery? Connect your DVOM in series between the negative battery terminal and its cable. With the meter set to the 10-amp scale, note the amperage. You may need to switch to a lower range after connection to get a more accurate reading.
In most cases, the current draw should be less than 150 milliamps. If it's higher, start by pulling fuses while watching the meter. When the current draw drops, you've located the group of accessories that may be causing the load. For exact specifications about normal key-off current drains, refer to a shop manual.
Finding The Missing
Ever have a customer complain about an engine that misses when it's damp out, but otherwise runs fine? Here's a tip for the next time you face one of those pesky problems.
Fill a spray bottle with water and run the engine while it's connected to your ignition scope. As the engine runs, spray the ignition wires with a mist of water, and note the pattern on the screen.
Wires with poor secondary insulation will allow voltage to sneak to ground, resulting in a dead miss. Also, watch for secondary voltages that drop suddenly and intermittently. To help provoke these problems even further, connect one end of a jumper wire to ground and run the other end across the length of each wire. Any leakage in the insulation will cause the voltage to jump to the jumper wire.
Grounds For Sanity
Ever encounter an onboard computer problem that seems to defy all your diagnostic logic, and the routines provided in shop manuals? If so, check to make sure that all grounds are clean and secure.
Why? The computer or one of its sensors may not be grounded properly, causing a difference in ground references and the amount of voltage being sensed. Since this difference can confuse the system, make absolutely sure that the gremlin you're chasing isn't just a bad ground.
Have you ever experienced a no-charge problem, and replaced the voltage regulator, only to have the car come back with the same problem ... again?
If the windings of the alternator rotor should develop a short, their resistance drops. This reduced resistance causes current flow to increase through the field windings, and through the regulator's field control circuit. Since the transistor in the voltage regulator is only capable of handling a certain amount of current, the transistor will eventually fail from current overload.
That's why it's in your best interest to check the alternator's field-current draw when you face a car with a failed regulator. If current draw is too high (normal current draw is around 4 amps), you'll want to replace the alternator and the regulator - before it becomes a comeback.
Lost time can never be made up, but by heeding some of the examples given here, you just might be able to beat the clock every now and then.
Questions or comments about this article, contact the author, Dave Cappert, at firstname.lastname@example.org.