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Test Light or AmmeterPosted 12/18/1997By Kevin Caple
For years, many technicians have been using a test light to determine if a car has a current draw. It was a fast, accurate and reliable method. So why is it that today we have to abandon the test light as a tool to check for current draw? It would probably be best compared to why we have abandoned the distributor, which resulted in more accuracy in timing off the crankshaft instead of off the camshaft. In current draw testing we have found - thanks to electronic memories in climate controls, radios, seats and multiple computers - the "old-reliable" test light is not as reliable as it used to be, not to mention that many test lights on the market today are using different current requirement bulbs. I've used my test light for 20 years. It takes about 100 milliamps to light, so if it lights up, I know I have a good-sized draw. Even using it on electronic cars of the early '80s, I knew the test light would come on bright when first connected. As capacitors were being charged up in the system, the light would become dim and then go out, indicating there was no current draw. When I purchased another test light so I could do multiple testing, it never occurred to me they would have changed bulbs in something as simple as a test light. Of course, that led to another diploma from the school of hard knocks! My new test light would light up at 30 milliamps instead of 100. And now we're using specs of anything less than 50 milliamps as an acceptable parasitic drain - well, between that test light misleading me and the newer cars with different systems that go to sleep (time themselves out and shut off) after a given period of time, which can sometimes take up to 10 minutes. (This would show a draw to be present until the time requirements have been satisfied, then the draw would go away.) I have now found that the only accurate way to check for current draw is to use an ammeter in series with the battery cable. The proper way to hook it up would be with everything shut off, disconnect the negative battery cable, then connect a jumper wire between the battery and cable (now the circuit is complete again). Next, set your ammeter on the highest amp scale and connect between the battery post and battery cable. Leave the jumper wire connected also. Now, walk away for 10 minutes (be sure the underhood light is disabled), come back and remove the jumper wire. All current flow is now through your ammeter and you can scale down your meter until you get a good reading. Most cars should be less than 50 milliamps. From this point, it is a matter of isolating circuits as normal to find where the draw is, if there is a draw at all. If I ask for current draw when you call, it's because we're not comparing apples to apples unless I know the criteria it takes to make your test light, voltmeter or magic probe work.
No start Ford T-birdPosted 12/18/1997By Mitch Belew
Have you ever encountered no power to the fuel pump on a Ford Thunderbird or Mercury Cougar with Electronic Engine Control 4 fuel control? Although many problems could contribute to this type of failure, there is one possible cause that you may not find right away. Like all other Fords with Electronic Engine Control 4 fuel control, the powertrain control module simply provides the ground needed to energize the fuel pump relay. The ground or trigger wire is routed to the self-test connector before completing the path between the powertrain control module and the fuel pump relay. Now for the kicker! At the self-test connector, the trigger wire is spliced together with the very same female terminal used as the fuel pump test lead. If the relay cannot be energized by grounding the trigger wire at the powertrain control module, but can be triggered at the self-test connector, take into consideration that the problem may be caused by a poor connection at the self-test trigger wire splice.
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