Washington, D.C. Centre
the Spark


by Jim Lunson


One of the more difficult electrical items to understand on our MGs is the starting and ignition system. This system does two things: first, it modifies the entire electrical system during the starting mode to put every ounce of battery juice available onto the starter motor, and secondly, it provides the electrical current to the spark plugs which need to fire in order to ignite the gasoline in the cylinders. Everything else electrical in the car is secondary to providing these functions: starting and running the engine. These other systems accomplish many different functions, and depending on the age of the cars, they vary greatly in their complexity. But the starting and ignition systems function about the same in all MGs, regardless of age.

The electrical function of starting the engine is accomplished by use of a relay. A relay is a type of switch that, when low amperage current is supplied to one side, it opens or closes a separate secondary switch that contains a much higher electrical current. In the starting system, in order to provide the starter motor with as much current as possible, this secondary circuit uses very heavy wire and thus requires a very heavy switch to connect it. It is so heavy that the item is called a solenoid instead of a relay, but functions the same. When a low amperage current (#16 or #18 gauge wire) flows from the ignition switch (key on or button) on the dashboard, it closes this heavy duty solenoid switch and sends a large current directly from the battery via the big fat wire (#4 gauge) to the starter. This heavy wire and switch get all the power possible from the battery directly to the starter to spin the engine fast enough to start. The starter motor has to be very powerful to spin the engine fast enough to start and it draws more current than anything else in the car. That is why it requires such a heavy wire and this heavy wire requires the big solenoid switch to make the contact.

The second thing this solenoid does is disconnect almost all other electrical current in the car. This is why the radio comes on when the ignition switch is in the run mode, but cuts off when the start mode is activated. Same for the blower, wipers, and just about everything else electrical in the car except the headlights. The idea, again, is to get as much power to the starter as possible, this time by cutting out everything else electrical that might suck current away from this effort. And its the reason you should not try to start the car with the lights on.

Have you ever turned the key or pushed the start button to start the engine and instead of the familiar whirr of the engine cranking, all you hear is a rapid clicking sound? This sound is the solenoid trying to engage the heavy duty switch to connect the starter, but due to a weak battery, gets just enough current to activate the solenoid but not enough to throw the heavy switch inside. Just enough electrical current to keep trying over and over: hence the clicking, but no contact and no starting. There is usually enough power still in the battery to run the radio, lights and most other electrical items, so the battery seems to be fine, but that starter motor requires so much juice that the switch just cant close to get the power through.

One possible solution when you hear this clicking sound short of getting a new battery is to check the connections on the battery and solenoid. Because this starting mode requires so much current, the connections are very large, providing a wide connection surface for lots of juice to flow through. If any of these connections gets loose or corroded, electrical current to run the car will still flow, but not when every ounce is required for that starter. So, when the clicking sound is heard, first check and clean these connections. This includes connections on the battery, the battery to frame ground, connection to the solenoid, to the starter and the engine block to frame. If that doesnt do it, then get a jump from an outside source and see about a new battery. I once had a battery that worked fine, until Ann and I stopped at an overlook in Shenandoah Park. A cloud rolled in on us while we were there (very pretty) and the sudden moisture from it was enough to weaken the connections. When ready to leave, the solenoid started clicking in stead of starting. Fortunately, we were able to roll downhill far and fast enough to jump start the car. Once, down the mountain and out of the cloud, everything was fine again. The moisture brought in by that cloud was just enough to weaken those big connections enough so there was not enough current. You'd better believe I cleaned and tightened those connections first chance I had.

I also recently saw an MG where the starter motor mysteriously burned out. In checking we found a faulty ground from the engine block to the frame. Adequate electric current got to the starter just fine, but it was unable to flow back to the ground and instead melted the coils in the starter. So be sure to check that connection also if there is trouble. It is usually way out of the way under the car by the transmission mounts, but is also a heavy wire and a crucial link in getting the starter to crank.

One item to note on car batteries these days too: new modern auto battery construction utilizes alkaline chemicals in lieu of the old acid types. This change permitted the sealed tops (maintenance free!) which eliminated the little removable screw caps that needing checking and occasional filling with distilled water (remember them?). In addition deleting this maintenance step, the newer construction lasts much longer. Warranties of 7, 8 or even 10 years are now not uncommon, whereas before 3 years was about the maximum you could get. So there has been great progress in this area of automotive science; however, one downside to this change is that the newer batteries tend to fail all at once rather than gradually losing starting power. You can start the car with almost full battery power, drive to the store, and find the battery completely dead when you get ready to return home. No warning, no weak starting, and no reviving - just dead, and often so dead it wont even provide the clicking sound described above.

So it pays more than ever to keep an eye on the age of your battery, not waiting for it to show signs of weakening before replacing it. And, if you wish to do a little easy preventative maintenance on your battery, check your paperwork to see how long you have had it and how long it is rated to last. Chances are if it is past the rated lifetime, you may be in for a surprise one time when you go to start your engine. It's easy to check and a replacement now may save a lot of headache.

I'll go over the ignition system in the next issue as to how the electrical juice gets from the battery to the spark plugs to get the engine firing. It's another system that is vital to the running of our cars and one that is often not understood. It involves coils, distributors, points and other exciting parts of our cars. How they all work together and what can go wrong.


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