next in order is contact No. 5, which is wired to coil unit No. 5. Following this comes timer contact No. 3, which supplies current to coil No. 3. While the individual spark coils are connected in order, i.e., coil No. 1 is joined to spark plug and cylinder No. 1, coil

No. 2 to spark plug and cylinder No. 2, and so on the timer contact must be numbered according to the firing order. It will be apparent that two sources of ignition current are provided for the battery and coil systems, one being a storage battery, the other a set of dry cells.

A double ignition system in which a true high tension magneto is used and a four unit vibrator coil and four point timer is shown at A, Fig. 69. This ignition system is for a four-cylinder motor having a firing order of 1-3-4-2. At B, Fig. 69, a triple ignition system for a four-cylinder engine is shown, this being practically the same as that outlined at Fig. 68 except that the wiring diagram is somewhat simpler owing to the lesser number of cylinders. The advantage of a double ignition system is that one can determine if irregular engine operation is due to the ignition system or not very easily by running the engine first on one system, then on the other. If the engine runs as it should on the battery system after it has been misfiring on the magneto it is reasonable to assume that some portion of the magneto system is not functioning properly. If the engine runs well on the magneto, but not on the battery, the trouble may be ascribed to failure in the chemical current producer or its auxiliary devices. On the other hand, if the engine does not run well on either ignition systems, it is fair to assume that the trouble is not due to faulty ignition. A non-technical illustration of one of the double ignition systems that were prominent before the general adoption of self-starters and when the high-tension magneto was not yet accepted without suspicion is shown at Fig. 70.

Battery Ignition System Troubles.-Ignition troubles are usually evidenced by irregular engine action. The motor will not run regularly nor will the explosions follow in even sequence. There may be one cylinder of a multiple cylinder, motor that will not function at all, in which case the trouble is purely local, whereas if all the cylinders run irregularly there is some main condition outside of the engine itself that is causing the trouble. The first point to examine is the source of current. Full instructions for the care and repair of storage batteries are given in following pages so we will first consider the simple primary or dry cells. It will be observed that a dry cell is very simple in construction and that nothing is apt to occur that will reduce its capacity except diminution in the strength of the electrolyte or eating away of the zine can by chemical action. The elements in a dry cell are usually combined in such proportions that about the time the electrolyte

is exhausted, the zinc can will also have outlived its usefulness. It is much cheaper to replace dry cells with new ones than to attempt to repair the exhausted ones.

Evaporation of the electrolyte is the main cause of deterioration of dry cells as the internal resistance of the cell increases when

the moisture evaporates. It is said that dry cells will depreciate even when not in use, so it is important for the repairman to buy these only as needed and not to keep a large stock on hand. In order to test the capacity of a dry cell an amperemeter is used as indicated at Fig. 71, B. Amperemeters are made in a variety of forms, some being combined with volt meters. The combination instrument is the best form for the repairman to use as the volts

scale can be employed for testing storage batteries while the ampere scale may be utilized in determining the strength of dry cells. A fully charged, fresh dry cell should show a current output of from twenty to twenty-five amperes. If the cell indicates below six or seven amperes, it should be discarded as it is apt to be exhausted to such a point that it will not furnish current enough to insure energetic or reliable ignition. Dry cells.

Grids at

Fig. 72.-Showing Construction of Storage Battery Plates.
Left of Illustration are Not Filled with Active Material in Order to
Clearly Show Skeleton of Plate,

should always be stored in a cool and dry place, so that the electrolyte will not evaporate. If moisture is given an opportunity to collect on the top of the pitch seal it will allow a gradual loss of current due to short circuiting the cells. In applying an amperemeter, care should be taken to always connect the positive terminal marked with a plus sign against the carbon terminal. In the indicating meter shown at B, it is necessary to use only one. contact point which is pressed against the screw passing through the carbon rod. The case of the instrument is placed in contact

with the zinc terminal to complete the circuit. A flexible wire is usually included in order to test the amperage of a group of cells should this be thought necessary. When dry cells are used for automobile ignition, they should be carefully packed in a box made of non-conducting material, such as wood, and securely covered so there will be no chance for water to enter the container. If placed in a sheet metal case, care should be taken to line the box with insulating material and also to pack the cells tightly so they cannot shake around. The best practice is to use wedges or blocks of wood which are driven in between the cells to keep them apart. In no case should a dry cell be placed directly in a steel box, as the binding posts on the zincs might come in contact with the walls of the box and tend to short circuit the cells, producing rapid depreciation. A battery box should always be placed at a point where it is not apt to be drenched with water when the car is washed or should be watertight if exposed.

Storage Battery Defects.-The subject of storage battery maintenance was thoroughly covered in a paper read by H. M. Beck before the S. A. E. and published in the transactions of the society. Some extracts from this are reproduced in connection with notes made by the writer and with excerpts from instruction books of battery manufacturers in order to enable the reader to secure a thorough grasp of this important subject without consulting a mass of literature. Endeavor has been made to simplify the technical points involved and to make the exposition as brief as possible without slighting any essential points. In view of the general adoption of motor starting and lighting systems on all modern automobiles, the repairman or motorist must pay more attention to the electrical apparatus than formerly needed when the simple magneto ignition system was the only electrical part of the automobile. The storage battery is one of the most important parts of the modern electrical systems and all up-to-date repairmen must understand its maintenance and charging in order to care for cars of recent manufacture intelligently.

A storage battery, from an elementary standpoint, consists of two or more plates, positive and negative, insulated from each