QuestionQUESTION: Howard,
I have been writing this week regarding refurbishing my HVAC blower motors. They are installed, and all is well. As you know, to remove them, requires releasing the two fuse blocks to hang from their wiring, but that did not seem to be a problem until I buttoned everything back up last night. I found I had no radio or power windows. I at first refused to bother you with something of electrical nature as that is both difficult to diagnose by email and one of my areas of expertise. I did locate, after a couple hours of testing and reading schematics, a failed relay which fed both circuits, a black, round 30/51-87, 85-86 which I was able to find several square ones of the same configuration on a later XJ6 Sovereign at a salvage yard today. Installing the new relay gave me back my radio and power window function, but on a drive tonight, the radio suddenly shut off, then back on, and I realized the engine had cut off. I was able to quickly restart the engine, but this happened again within moments. at this point, I feared an alternator failure, so I shut off the radio and trip computer, dimmed the gauge lights and headed home. When I got home, I had to shut off the car to use my keys to unlock the garage, and it would not start back up. At this point, I thought I surely had a failed alternator, and had been driving on battery alone. My battery charger quickly, as in less than 5 minutes, charged the battery to 100%, and when started again, I read 14+ an the battery, indicating the alternator was ok. I abandoned the car at that point in disgust, but before I dig back in, do you have any suggestions, or have I perhaps simply done something careless in my fondling of the under dash wiring this week?
Thanks!
Michael
ANSWER: I found when working in dealerships that electrical problem symptoms would sometimes lead you to a section of a car. But any further than that the symptoms were useless. First is it almost impossible to locate a problem that happens on occasions. You need the problem to be present when testing. I did have to build a test box with LEDs and connect each LED to a suspected wire when it would only act up when driving. This way I could watch powers and grounds in action when I drove the car and when a light went out even for a second or two I was able to catch what was wrong. I used LEDs because of the low amp draw and I could even monitor signals to and from the ECU for injection problems.
It is easy to take a wiring diagram and trace a dead circuit to locate a fault but the intermittent fault require some method to monitor that circuit at all times.
As for using different relays, there is no problem as long as you know the number/letter ID of the terminals and the amp rating is high enough for what you are going to use it for. That was a common practice in most shops I worked in when the exact replacement was not available.
Keep in mind that the Series III Jag requires a "Deep Charge" battery (Diesel or Marine) and even when you have that, when the battery gets a little age on it, the car will start to act up. Starter spins the engine fast but it don't start. The test is to connect a known good jumper battery to the car as though the car battery is dead and if that starts the car you need a new "Deep Charge" battery. The old battery will then be useful in other kinds of cars for sometimes years. This always gave me a supply of free batteries for other cars when they failed in the Ser. III Jags.
Howard
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QUESTION: Thanks, Howard
It is tough to say whether this is truly intermittent yet, as it occurred on the first drive after the work I did this week, and has not yet been tested further or repeated. That is why I thought I would collect your thoughts before I go back to it. My basic diagnostic approach is that 4 days ago, I had none of these problems, now I do. So, what changed in the interim? What changed is that I monkeyed around with a lot of wiring, pulling and shoving things that I was not working on out of my way to get to what I was working on. Now that I have corrected what I set out to fix, I have other, new problems. I can grin and bear that. I can say the battery is almost exactly 3 months old, and I keep it charged, making sure it is "full", especially when I have completed long bouts of testing. I have read your answers to others about deep cycle batteries, and I'll consider that; but I think and hope I have done something accidental and foolish here. Serendipity is present as having no radio on the return trip alerted me to a need to replace the rear brake pads as well.
Thanks,
Michael
AnswerOf all the electrical problems I found over the years working on Lucas cars the most common were loose and bad connections. And as you may have run into, when fighting with a harness it is easy to end up with other problems when fixing one.
Loose, bad connections and switches are what gave Lucas the handle, "Prince of Darkness" I liked their color coding of wires as it was consistent on all British cars. After working on MG, Triumph & Jag for years I was able to go under the dash on an old Bentley and without a wiring diagram ID most of the wires in a harness.
I have Italian car experience too and a friend use to always call my MG "Prince of darkness" when he had a 124 Fiat. I had to remind him that the MGB and the Fiat 124 had basically the same number of electrical equipment pieces and the MG had 4 fuses that rarely would blow and a harness about one inch in diameter and the Fiat had dozens of fuses and a harness about 2 inches in diameter and color codes that didn't match any of the dozen diagrams available for the car and all you had to do was sneeze in the car and it would blow 5 fuses.
If you intend to keep the Jag you should contact Jaguar to see if publication "S 57" is still in print and available. It is the Series III book of wiring diagrams and locaters.
Howard
