central52 Posted March 23, 2015 Report Posted March 23, 2015 On my 47 Dodge, the battery is connected with the neg post to the engine block, and positive post to the starter unit. Is this right? I thought all mopars are positive ground. But, all electrical systems work O.K. lights, horn, heater, clock, car starts and runs. Hmm? Ed Quote
Don Coatney Posted March 23, 2015 Report Posted March 23, 2015 Does your charging system work? Does your amp gauge go to the positive side when the generator is charging? Quote
casper50 Posted March 23, 2015 Report Posted March 23, 2015 it could have been changed to negative ground. It's pretty easy to do. As Don says the gauge will tell you if it's right. Quote
greg g Posted March 23, 2015 Report Posted March 23, 2015 Which terminal one the coil is the wire from the ign switch connected to? Quote
50fordtruck Posted March 23, 2015 Report Posted March 23, 2015 My P15 Plymouth had been changed when I got it and the wires had been reversed on the amp meter so it showed correct. When I change it back to positive ground I had to reverse the wires on the back of the amp meter to show correct reading. It worked ok that way I just wanted it as original. Phil Quote
central52 Posted March 23, 2015 Author Report Posted March 23, 2015 The amp gauge shows positive reading. Ed Quote
casper50 Posted March 23, 2015 Report Posted March 23, 2015 It most likely has been switched to negative ground then. Quote
fordkustom Posted March 24, 2015 Report Posted March 24, 2015 You will find out if you drive around a few days and have a dead battery. For a proper change to neg-ground system the entire charging system would need to have been rewired. It will still "work" if its neg ground hooked up but the charging end will be faulty and run the chance of ruining some parts of the system. Quote
central52 Posted March 24, 2015 Author Report Posted March 24, 2015 Well,l guess it's o.k. I've had the car a few months. Took it for rides once in a while. Amp gauge always shows positive. I don't know if the previous owner did any rewiring, but it appears that it's charging and nothing bad has happened so far. I dread going in there changing a lot of wires, if I don't have to. Ed Quote
greg g Posted March 24, 2015 Report Posted March 24, 2015 I repeat my question, to which coil terminal is the wire from the ignition switch connected? Quote
Plymouthy Adams Posted March 24, 2015 Report Posted March 24, 2015 (edited) Greg...relationship to the coils wire primary is not relevant as it will run either way with either battery polarity orientation..some argue there is a loss in spark due to current flow..it is so minimum it is not worth mentioning..,..mainly the only true change will be the swapping of the transfer on metal on the contact point to the opposite face.. Edited March 24, 2015 by Plymouthy Adams Quote
greg g Posted March 24, 2015 Report Posted March 24, 2015 I was led to believe that when grounds reversed, coils tended to run hotter. And it was a good indication of the earth change being planed or done inadvertently and left as it seemed to run OK. Quote
T120 Posted March 24, 2015 Report Posted March 24, 2015 An excerpt from Gus Wilson's Model Garage,Sept 1965. ..... "I don't know about the man," said Gus, "but you've sure got the wrong car. This one never ran away from you at 90." "How do you know?" "It couldn't have," said Gus. "You couldn't push it over 75. The coil polarity is reversed. This pencil test is an easy way to show it. If the spark feathers are on the plug side of the pencil, polarity is okay. But when the feathers are on the cable side, the positive of the high voltage is connected to the center plug electrodes. That ruins performance, because it will take much more voltage to fire a plug." "Don't see why," said Eldon. "Most cars have the negative battery post grounded, but some have the positive." Gus grinned. "Makes no difference whether a car has negative or positive battery ground. The high-voltage polarity should always be negative at the plug terminals. It boils down to something called electron emission, on the theory that current is a flow of electrons, from the negative side to the positive. "The hotter something is, the easier electrons can hop off it. The center electrode of a spark plug gets much hotter than the outside one, which is attached to the shell and loses heat to it. So for easiest current flow and the best spark, the hot center electrode should be negative. If you make the outer electrode negative, you're forcing electrons to jump off a cooler surface to a hotter one. That's like bucking one-way traffic in the Friday-night rush hour." "The engine runs, so there must be an ignition spark," said Eldon. "Sure, at ordinary speeds. But spark-plug engineers say it takes up to 45 percent more voltage to fire a plug with reversed polarity. That cuts down on your voltage reserve. On heavy acceleration, when compression goes up and it's harder for the spark to jump, you get misfiring. Same thing at high speeds, when the points can't stay closed enough to build up a maximum magnetic field in the coil. Sam, this car couldn't have got away from you, let alone run for miles at over 90." "Okay, maybe it couldn't. Now what does it take to reverse this polarity?" Gus pointed to the coil terminals. "Just switching around these two wires.".... 3 Quote
Lloyd Posted March 24, 2015 Report Posted March 24, 2015 (edited) Thanks Ralph. very informative. But wuts a pencil test? Edited March 24, 2015 by Lloyd Quote
_shel_ny Posted March 24, 2015 Report Posted March 24, 2015 (edited) Thanks Ralph. very informative. But wuts a pencil test? http://www.sparkpeople.com/myspark/team_messageboard_thread.asp?board=0x41173x32541732 or Popular Science Sept 1965 https://www.google.com/search?q=spark+pencil+test&ie=utf-8&oe=utf-8 Edited March 24, 2015 by shel_ny Quote
greg g Posted March 25, 2015 Report Posted March 25, 2015 Www.Mgaguru.com/mgtech/ignition/ig104.htm 1 Quote
Tony724 Posted March 25, 2015 Report Posted March 25, 2015 Www.Mgaguru.com/mgtech/ignition/ig104.htm I just bookmarked that. Never seen that pencil trick before! Quote
central52 Posted March 25, 2015 Author Report Posted March 25, 2015 Wow, the things you learn on this site. Will check that spark test, and coil terminal wire to ignition switch. Ed Quote
central52 Posted March 28, 2015 Author Report Posted March 28, 2015 well, I tried to do that pencil test, but I couldn't get the spark plug wire close to the spark plug to make a spark. The wire was enclosed in a thick outer L shaped cover. Not open like in those pics on the other site. But here's a pic of the coil wire connections. The blue tabbed one wire goes to the distributor, the yellow to the starter switch. So, am I good to go? Ed Quote
greg g Posted March 28, 2015 Report Posted March 28, 2015 The terminals should be labeled + and -. Can you feel which is which or use a mirror:-) . Quote
Niel Hoback Posted March 29, 2015 Report Posted March 29, 2015 The terminals on the coil should be marked + and - . If your battery is positive ground, then your positive coil terminal should go to the distributor. 1 Quote
_shel_ny Posted March 29, 2015 Report Posted March 29, 2015 The terminals on the coil should be marked + and - . If your battery is positive ground, then your positive coil terminal should go to the distributor. Niel, thank you for putting the end to the game of 20 questions Quote
central52 Posted March 29, 2015 Author Report Posted March 29, 2015 Checked the coil markings. The yellow tabbbed one is on the positive side, the blue on the negative. Right now, that yellow tabbed postive wire is going to the starter switch. Which means, according to Niel, that's it's a negative ground system. Am I right? So, everything is at it should be? Ed Quote
Niel Hoback Posted March 29, 2015 Report Posted March 29, 2015 It sounds like some one has already changed the car to negative ground. If your ammeter shows a charge when the motor is running, then you are all set. Nothing else needs to be done, even an original radio will work grounded either way. Quote
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