Brad Clayton Posted August 20, 2011 Share Posted August 20, 2011 A co-worker asked for some assistance with an electrical problem the other day. I was glad to help out as always. The shop has a new hire that changes oil and he was not busy so I had him join in the fun as well. The vehicle was a 2007 Town Car with a driver’s window inop. When we arrived on the scene, Ben was already in the middle of his diagnosis. The problem he was having was the fact that the window motor connector showed 12 volts on a meter while the motor was unplugged. Major confusion was amassing and I had to explain the effects of a weak circuit. We dug out the EVTM and I suggested plugging the motor back in and powering up the circuits with a power probe at the switch connector. The motor worked fine and a switch was ordered up and installed. The car was released to the customer and all parties involved were satisfied, except for our new apprentice. Bill was left out in the cold on what went down. We were flat rating the diagnosis and needed to move on. I could tell he was overwhelmed and decided to walk him through what took place. We sat down in the break room later that day with the shop manual and the EVTM. I handed the manuals to Bill and said we have a window inop, what now? I let him navigate through the shop manual and we started at pinpoint test “B”. Pinpoint tests in shop manuals can be confusing as hell without the EVTM. We followed the pinpoint test to a “T” and came up with a faulty motor. Huh? We know that the fix was a faulty switch. Ford decided it was a good idea to put high current components and delicate components in the same location and jam them in the rear of the switch. The book wanted the switch bench tested. It worked just fine on a bench using a volt/ohm meter. However it did not work at all when more than an amp (much less 9 or 10 amps) was tried to push through it. So we wrapped up the conversation with the idea of not getting the end of your nose to close to the book (tunnel vision and the like) and we talked about the effects of electricity with high resistance, corrosion, and a 10 strand wire with only 1 strand intact. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted August 20, 2011 Share Posted August 20, 2011 I might suggest spending some time with both of Kirschoffs laws. As for the PPTs for this kind of stuff in Fords WSMs????? Why would anybody waste time reading that ignorant pap? Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted August 20, 2011 Share Posted August 20, 2011 In retrospect, I suppose I might expound on some of this stuff.... Time and again I have remarked about Fords willingness to publish some of the most inappropriate circuit testing that you could ever hope to see. If we blindly follow their PPTs, we will replace every big dollar part in the system before we realize that all we really need is to resort to "proper volt drop testing". Step one.... verify the power supply - is the fuse intact? Step two - establish you baseline voltage. What is your system voltage with the vehicle set up for your tests? It is important to maintain this voltage level throughout your testing. Step three.... go to the non-functioning load. You absolutely need to apply your DMM leads to the load itself.... operate the circuit. You will get one of three results.... System voltage, zero volts or something in between. What we see here will decide our next step. Proper volt drop testing will reduce the amount of time spent diagnosing circuit concerns - Ford SLTs only pay something like .3 for this test. Learning how to do it efficiently will maximize your earning potential. FWIW, your illustration would be "step two" in a proper circuit diagnosis. Quote Link to comment Share on other sites More sharing options...
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