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Put Away That Test LightPosted 3/10/2003By Dave Sill
Remember the good old days, when you could check for a battery draw with a test light? Well, when it comes to testing the newer Ford products, those good old days are definitely gone! In fact, I'd say that if you disconnect one of these vehicles' battery cables and connect your test light between the cable and the post, and the light doesn't come on, then it's time to replace the bulb! For quite some time now, it's been a good idea to use an ammeter, rather than a test light or voltmeter, when checking for a battery draw, but when it comes to checking out mid-1990s or newer Ford products, it's strictly a necessity. Most hand-held automotive digital volt-ohm meters (DVOMs) have a DC ammeter function that will read DC mA (milliamps) and DC amps up to 10 amps. The meter should contain a fuse for the amps' function to protect it from excessive current. If it doesn't say "fused" next to the DC amp dial position, a 10-amp inline fuse should be installed in one of the meter leads to protect the meter. Also, most DVOMs have a special jack to connect the red (positive) lead for current measurement. If possible, the DVOM should be connected to the vehicle in such a way that the connection is never broken between the battery and the vehicle. The easiest way to do this is to install a "battery saver" or "anti-theft" switch between the battery negative post and the cable. These switches are readily available through the aftermarket. They have a knob that can be loosened to break the connection between the battery cable and the battery post after securely connecting the positive ammeter lead to the cable side of the switch and the negative lead to the battery side of the switch. Here's a less reliable but equally effective method - if carefully done:
Either way will prevent false high readings due to capacitors throughout the vehicle trying to charge through the ammeter, and can also prevent blowing the meter's fuse (for instance, some newer Windstars will actually flash the headlamps once every time the battery is disconnected and reconnected). Once the ammeter has been connected, then the fun really starts. Expect readings in the 300-400 mA (0.3 - 0.4 amp) range on most newer Ford products. In fact, some vehicles will have readings as high as 850 mA (0.85 amp). Automotive technicians have been trained that anything over 50 mA is an excessive draw, so these readings will immediately raise a red flag, but they are normal! Most, if not all, of the newer Ford vehicles have modules that will remain in "stand-by" mode for a period of time after shutting the vehicle off, and in this mode, will draw enough current to cause these readings. The length of time the modules remain in this mode will vary by model. As a rule of thumb, if you wait for one hour without touching the vehicle, the modules should go into "sleep" mode and current draw should be well below 50 mA. Keep in mind that opening or closing any door, hood or trunk lid, inserting or removing the key, or activating any electrical switch can cause a module to "wake up," in which case the time-out period will start over. Also, many DVOMs have their own sleep mode that they will go into after a period of inactivity. If this happens, a press of any button on the DVOM will normally wake it up. By following these procedures, you should be able to spend less time trying to troubleshoot normal initially high current draw readings on the newer Ford vehicles, leaving you more time for fixing real problems and making money.
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Copyright (c) 1996-2009. Automotive Service Association®. All rights reserved.
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