jrhoads Posted January 18, 2015 Report Posted January 18, 2015 Gents, Can you tell me what this part is? I am doing a 12v conversion and tidying up thiings which mean splicing and re-routing so things look nice.However, I dont know what this is let alone where I get another one. It was mounted on the firewall. Wires in order go to: 1. Positive side of starter selenoid. 2. Ties into the wires that go forward to the front lighting. 3. Negative side of the coil. 4. Believe it or not, the wire goes down to the steering box and goes inside it. Wierdest thing.... Anyway, any help on this would be apprecaited. I looked over the forum and tech areas and even looked a shop manual and elec diagram and could not figure this out. Thanks in advance. Quote
jrhoads Posted January 18, 2015 Author Report Posted January 18, 2015 Yep. I just figured this out after scratching far enough to find the numberts on it. Thanks guy and thank you for the diagram as well. Best Regards Quote
Adam H P15 D30 Posted January 18, 2015 Report Posted January 18, 2015 If you are converting to - ground also, the lead marked neg coil will change to + coil. Quote
jrhoads Posted January 18, 2015 Author Report Posted January 18, 2015 Thank you. The new relay included has only three terminals: Horn, Switch and Battery. As I understand it, the old relay had a junction point to power several items that required power only with the ignition in the on position. So when wiring the new ignition coil in now, what was on the negative side of the coil coming from the top of the firewall through that conduit type apparatus, will now be on the positive side of the coil correct? Quote
Adam H P15 D30 Posted January 18, 2015 Report Posted January 18, 2015 Correct. If you run an external resistor the coil lead to the relay will attach to the non resisted side(firewall side). Also, change to a 12v relay. Quote
Don Coatney Posted January 18, 2015 Report Posted January 18, 2015 My statement below in blue is incorrect. Sorry for the bad information. The statement below in black is from an International Harvester service manual and has the correct information. In a DC (Direct Current) circuit current flows from negative to positive. And in a DC circuit the heavy arcing occurs on the negative side when the circuit is interrupted. So the only difference in the coil/point power supply is the side (top or bottom) contactor of the points will receive the heavy arcing. The system will work the same when changing from positive ground to negative ground with the exception of the contact point arcing. So it is not necessary to change the polarity on the coil wiring as the system efficiency is exactly the same. COIL POLARITY One of the major causes for hard starting or spark plug misfiring under load results when the ignition coil lead wire to the distributor is installed on the wrong side of the coil. This condition causes reversed coil polarity. Voltage at the spark plug terminals should always be negative. Whether it is or not depends on how the primary leads are attached to the coil. Remember, primary lead hook- up directly affects coil polarity, which in turn determines whether voltage at the spark plug terminals is negative or positive. On IH trucks the distributor wire to the coil should always be placed on the negative side of the coil if the electrical system is negative grounded, or on the positive side if the electrical system is positive grounded. If the primary leads are incorrectly attached, the direction of current flow through the coil is reversed. Consequently, coil polarity is reversed, resulting in positive voltage being supplied to the spark plug terminals. What difference does it make whether positive or negative voltage is supplied to the spark plug terminals?. It directly affects the amount of voltage required to fire the spark plugs. When polarity at the spark plug terminals is positive, it's harder for the voltage to jump across the air gap than when polarity at the plug terminal is negative. Just why this is so is related to a pair of electrical theories--the electron theory and the theory of thermionic emission. According to the electron theory, all current flows from negative to positive. The theory of thermionic emission states essentially it's easier for electrons to leave a hot surface than a cold surface. Combining the two theories, one finds that electrons will always leave a negative charged surface for a positive charged surface, and they will leave the negatively charged surface with more ease when the surface is heated. Spark plug design is such that the center electrode almost always operates at a higher temperature than the ground electrode. Since it's easier for electrons to leave a hot surface, it is preferred to have the electrons "jump" from the hotter center electrode to the cooler ground electrode. When the center electrode is negatively charged (negative voltage at the spark plug terminals), this is what happens. Stated another way, putting the negative charge on the hotter center electrode causes the gap to be ionized at lower voltage. (Ionization is necessary to permit passage of the spark through the high resistance of the gases in the cylinder.) When positive voltage is supplied to the plug terminals, which happens when coil polarity is accidentally reversed, the hotter center electrode becomes positive charged. Consequently, electrons must leave the negative charged ground electrode and move to the positive charged center electrode. But, since the ground electrode is cooler than the center electrode (and remember, it's easier for the electrons to leave a hotter surface), it takes more voltage to make the current jump the gap-in fact, up to 45 percent more. See Fig. Link to the complete article. http://firetrucksandequipment.tpub.com/TM-5-4210-230-14P-1/css/TM-5-4210-230-14P-1_545.htm 1 Quote
Adam H P15 D30 Posted January 18, 2015 Report Posted January 18, 2015 As I always understood it, wiring the coil leads backwards will result in a weak spark?? Quote
Don Coatney Posted January 18, 2015 Report Posted January 18, 2015 Should make no difference as the coil winding count is the same. 1 Quote
48mirage Posted January 19, 2015 Report Posted January 19, 2015 As I always understood it, wiring the coil leads backwards will result in a weak spark?? The difference will be in the spark at the plugs. With the coil wired backwards the ground electrode will deteriorate sooner. 1 Quote
Don Coatney Posted January 19, 2015 Report Posted January 19, 2015 As I always understood it, wiring the coil leads backwards will result in a weak spark?? The difference will be in the spark at the plugs. With the coil wired backwards the ground electrode will deteriorate sooner. You are correct. See my amended statement above. 1 Quote
greg g Posted January 19, 2015 Report Posted January 19, 2015 (edited) OK wait a second here. This talk of center electrode being the hotter surface is debatable. The center is partially enveloped in a ceramic insulator which is bonded to a portion of the plug that is in contact with portion of the head that is surrounded by circulating coolant. How can that be hotter than the lesser mass of the grounding electrode hanging out in the combustion chamber,that only gets cooled by the rush if intake air fuel mix, which almost immediatly heats up again under compression of that same charge? Sounds like voodoo engineer speak to me. Edited January 19, 2015 by greg g Quote
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