Machines and Manuals – Tools of The

Trade

Whenever a repair shop calls me asking for a freshly trained technician (and it happens fairly regularly), one of the first questions I ask is what type of shop manual resources the shop has.  My students are accustomed to having the shop manual material they need on hand.  Alldata is a great tool, and the students really enjoy using it, but I also have some dealer-specific shop manual software available in order to give the students a broader understanding of how different manufacturers lay their books out. 

As technicians, we must have shop manual data on hand in the form of facts, figures, wire maps, system descriptions, and all the rest of it in order to function effectively with our diagnostics so as to surgically repair today’s vehicles.  In addition to the shop manual data, we need the tools and know-how to retrieve vital information from the vehicle we’re working on, and we must be able to sort and interpret the data we gather in order to make a dependable judgment on what needs to be done.

To gather the facts and figures from the vehicle itself, we depend on our diagnostic equipment (scan tools, meters, o-scopes, etc.), and higher-end scan tools now have technical service bulletins and in some cases, even connector pinout images and normal sensor voltages stored in their memories. A really good handheld o-scope will have typical scope patterns stored as well.

With all the technology today, it seems as if somebody somewhere would make a fitz-all tool that would do anything on any manufacturer’s vehicles that the dealer tools will do.  Well, such a tool doesn’t exist. 

In 1991, when Ford introduced Hewlett Packard’s Service Bay Diagnostic System for Blue Oval cars, I signed for it at our dealership and by the time the trainer guy showed up to give us instruction on how to use it, I had already put the SBDS through most of its paces. 

Well, I sent a lot of honest feedback to the folks in Dearborn; I told them the SBDS was a good machine and why I liked it.  Then came the day it decided to be not-so-friendly.  I kept trying to trust the data the SBDS gave me and burned most of a day fooling around that way until I finally decided to disconnect the machine and fix the F-150 the old fashioned way.  After the battle was won, I attached a two-page carefully typed letter giving Dearborn the rundown on the problems I had trying to utilize the SBDS machine on that particular truck. Well, because almost all of my input on the SBDS had been positive, I got six phone calls and two personal visits from Ford people, all of whom had read my letter and wanted to see what they could do to make it right. 

The point is that it’s easy to focus on negatives, and those of us who tend to do nothing more than complain would do well to remember the fact that positive feedback is extremely important, especially whenever we get a chance to talk to the folks on the other end of the line who can make a difference. If you want ‘em to listen, then don’t complain all the time. The positive feedback principle is as important when we as technicians are interfacing with the local head shed as well.

 Now that I’m through digressing, let me say that it can be really irritating when the shop manual seems to have become a part of the problem, and this month’s diagnostic story focuses on just such an occurrence.  Admittedly, shop manuals are difficult to write, and for the technician who uses it for a guide, a simple little wiring schematic error can lead to hours of unnecessary labor. And while I’d like to blame the shop manual schematic this time around, I realized after the fact that there was something I had overlooked when I was studying the schematic.  So much for blaming the manual!

Lots of Different Drivers

        This month’s vehicle is a Taurus Wagon, a do-everything vehicle belongs to the college where I teach auto mechanics. The Taurus is one of two passenger cars the faculty and staff use for college business, and just about everybody on campus has had carnal knowledge of this comfortable old bomb at one time or another.  It seldom has the same driver twice in a row.  Everybody that uses the Taurus records the elapsed mileage and any noticeable concerns on a special form. The college receptionist keeps the keys and passes the needed service requests on to me.  In this particular case, the receptionist reported that the Taurus had been jumped off twice but that the battery kept going as dead as a doornail between drivers.  My students were all neck deep in other live work jobs (engine and transmission swaps and repairs), so I tackled the Taurus myself.

          True to form, somebody somewhere had popped a new battery in the box thinking that would take care of the problem, but it went just as dead as the one they replaced. A quick charging system test showed the generator output at about 85 amps idling with the weak-but-recovering battery, so it was time to look beyond the charging system.  There were no lights on or electric motors running anywhere with the key off, and the battery cables were clean and tight. So much for visible or audible possibilities.

A couple of interested students took some time away from their live work jobs to get a short refresher on how best to find a parasitic drain.

Connecting a low impedance test light between the negative battery terminal and the negative battery post, I saw a bright and steady glow (a pulsing light is normal on many new cars), the clearest indication of a battery-killing draw.  Briefly touching the battery terminal to the post with the light still connected sometimes charges up a capacitor circuit somewhere and eliminates the indicated drain, but in this case it made no difference. 

Contrary to the olden days, some battery drain on modern vehicles (mid 1990's/up) is normal because of all the computers and stuff that have to remain awake while the vehicle is shut down. A basic rule of thumb on today’s vehicles is that a drain of 50 milliamps or more is too much. You can measure the exact amount of draw by replacing the test light (shown above) with a digital multimeter that is capable of measuring amps, and just about any parts house has one for sale, some for as cheap as 10 bucks.

An energized ISO relay coil will pull 50 milliamps and can kill a fairly strong battery in about two days. In the early nineties, manufacturers began making arrangements on some vehicles for this normal battery drain to either be neutralized by the body computer after a while or eliminated by the removal of a particular fuse or relay during storage. For example, consider Chrysler’s Ignition Off Draw (IOD) fuse, which feeds radio and courtesy light circuits, and is meant to be removed during shipping and storage. 

Disconnecting the test light, I set up a digital multimeter to measure current and found that the parasitic drain exceeded the meter’s 10 amp capacity.  Reinstalling the test light, I disconnected the external voltage regulator (the 1992 and earlier Tauruses are equipped with a rather antiquated 100 amp external regulator generator) and the generator, but the draw remained.

Removing the Power Distribution Center (PDC) maxi fuses one at a time while watching the improvised load light can eliminate large blocks of vehicle wiring.  After a particular wiring tree has been isolated, the interior panel fuses fed by the maxi fuse that killed the load light will further narrow the problem down.

 Reinstalling the load light at the battery and opening the PDC cover I found that removing one particular 60 amp maxi fuse eliminated the draw.  It was time to see what that fuse was feeding.

            A quick look at page 13-22 of the EVTM pages in Alldata showed circuit 38 fed the headlamp switch, but at the time I didn’t clue in on the fact that the circuit fed anything else.  The headlamps weren’t on but I found myself wondering if the headlamp switch connector had suffered some sort of meltdown to the point that two circuits were touching. 

Removing the instrument cluster bezel, I accessed the headlamp switch and disconnected it.  The headlamp switch connector wasn’t showing heat damage and disconnecting it made no difference on the draw. 

I followed the harness from the PDC to connector C101 near the driver side shock tower, and when I disconnected it, I found that the draw went away; This put the problem between the C101 connector and the underside of the dash.  Glancing at the schematic I had printed, I came to the conclusion that something had gone haywire between C101 and the headlamp switch that was drawing current out of the battery.  It looked as if I might have to clip that part of circuit 38 out and run an overlay, but as I examined the C101 connector a little more closely I found that there were two identical black/orange 10 gauge wires passing through the connector. 

Something was fishy; when Ford has a heavy load-carrying circuit that has to pass through a single connector, they sometimes split the circuit with a splice and pass it through two cavities so as to share the load between two terminals.  In that case, both wires will generally be the same color as they were here.  It appeared to me that Ford had done exactly that in this case, but why didn’t the schematic indicate that there was a splice in the circuit?

            Flipping back through the Power Distribution part of the manual (there are more than a dozen pages in that cell), I came to another page that also pictured the 60 amp headlamp fuse, but there was a big difference. 

 The circuit breaker shown in the fuse panel here (marked c.b.), feeds the lighter on this Taurus... the circuit breaker can reset itself, unlike a fuse that is blown and done for when a short occurs!

 This one showed the splice that the previous schematic didn’t, with one fork going to the headlamp switch and the other fork (both through C101) going to feed several smaller fuses and one circuit breaker in the fuse panel.  Leaving the load light in place, I moved to the Instrument Panel fuse box (it releases and folds down on earlier Tauruses for really easy accessibility) and found that removing the circuit breaker killed the draw.  I was getting closer. 

To make a long story short, (too late, I know) I found a penny in the cigar lighter.  It wasn’t immediately noticeable because some yo yo had put the lighter in on top of it.

      The only clue on the first schematic that I missed (and I shouldn’t have) was the almost unnoticeable break in the drawn circuit (see illustration) between the fuse and connector C101.  That was supposed to clue me in to the fact that the entire circuit wasn’t shown, but Ford has about two or three different ways of doing that, and the circuit break was easy to miss.  Usually, a splice will be pictured, sometimes accompanied by a wire ending in an arrow and a little note that leads to another page.

            Usually a penny in the lighter will blow a fuse, but in this case, the circuit breaker allowed the current to keep flowing, and the penny made a nice load, since only a small portion was actually conducting current into the whole coin.  It would have been a silly disaster to have run an unnecessary overlay because of an overlooked schematic reference and a penny in the lighter. Had the lighter not been hiding the penny, and if I been more attentive to the schematic, I would have found the problem sooner.                                                                                                                                                                                                                                                                          R.W.M.