bambamshere Posted March 29, 2017 Report Posted March 29, 2017 (edited) Hello I have a 56 Fargo and was wondering how I would figure out if I have a external resistor or not. The truck has been converted to 12 volt. There is nothing I can find on the ignition coil. All it says is 12v. I have looked around the truck but haven't seen anything yet. Could it have been put under dash. How would I figure out if there is one in the ignition coil it self. By the way it has a Flathead 6 in it Edited March 29, 2017 by bambamshere To put engine type in the comments Quote
Plymouthy Adams Posted March 29, 2017 Report Posted March 29, 2017 read the primary circuit ohm rating and see if it is an internal resistor coil. Many folks use these for the simplicity of not mounting an external resistor and a by pass wire to start on 12 and run on 6 but they do it at the expense of their points. The internal resistor coils keep a higher voltage for a longer period of time over the "switched" circuit that is the external resistor... if you primary is rough 3.2 ohms...you internal resistor.. rule of thumb on the external if you not racing and full saturation at x-rpm is not critical...is that the dropping resistor should be that of the coil's primary resistance... 1 Quote
classiccarjack Posted March 30, 2017 Report Posted March 30, 2017 (edited) Plymouthy Adams is spot on. I have found burned up points on cars that have had 12V conversions done. I always use a ballast resistor on my projects and or resistor wire for the GM guys. Points installed by me last like they should. And protecting your points is important. Getting stranded is no fun! I hope that Plymouthy Adams information is beneficial to you. It really is good advice. Edited March 30, 2017 by classiccarjack Mispelling Quote
Don Coatney Posted March 30, 2017 Report Posted March 30, 2017 New 12 volt coils are marked as pictured if an external resistor is required. Quote
Dartgame Posted March 30, 2017 Report Posted March 30, 2017 take a volt ohm meter and read the voltage to the coil. if is 12 v when running you probably should install a resistor to the feed for the coil. normal running voltage should be around 8 volts for most stock style 12 volt coils. Quote
classiccarjack Posted March 30, 2017 Report Posted March 30, 2017 5 hours ago, Dartgame said: take a volt ohm meter and read the voltage to the coil. if is 12 v when running you probably should install a resistor to the feed for the coil. normal running voltage should be around 8 volts for most stock style 12 volt coils. Both Don and Dartgame are right. Be sure it's not too much resistance after the vehicle gets to operating temperature. This is why... I chased my tail on a customer car once. Once his car warmed up the spark would cut out and cause his car to stall. When cold, he had about 7.75 VDC. Once it warmed up initially, it dropped to 5.98 VDC. After it ran for 30 minutes, it would drop below 5 VDC and start causing the engine to cut out and sometimes stall. We both thought it was just running out of gas at first, then I finally figured it out... I know that this is TMI, but I hope it helps someone in the future.... 1 Quote
bambamshere Posted March 30, 2017 Author Report Posted March 30, 2017 Thanks for the responces I am trying to figure this out not because the ignition coil is bad or anything. It has probably been sitting on the engine for 30 to 40 years as this engine came out of a 1950's combine and it is pretty rusty. Quote
Plymouthy Adams Posted March 30, 2017 Report Posted March 30, 2017 the tractor/farm implement guys have been log ahead of the learning curve on upgrade to 12 volt and use of the many "one wire" advantages both is alternator and coils...again, be certain the coil requires an external resistor....a internal resistor coil in combination with an external resistor inline leads to a condition stated above...after the coil's resistor comes into full play when hot, combined with the external your voltage drop is to great for saturation of the coil and therefore you secondary voltage is quite less....I have seen this in a number of old cars when folks mix and match components handed to them by some uknowning counter clerk....always check behind them.... Quote
bambamshere Posted March 30, 2017 Author Report Posted March 30, 2017 (edited) Is there a way to open the coil to see if there is a internal resister inside of it. I have been through the trucks wiring and have seen only 2 wires to the coil a positive and a negative. I'm guessing that means nothing when it comes down to it. Edited March 30, 2017 by bambamshere Spelling words wrong Quote
Plymouthy Adams Posted March 30, 2017 Report Posted March 30, 2017 you can sometimes tap on the bottom and determine if it is a hollow can section..without the part number visible on the coil...I would not play guessing game, use the ohm meter and KNOW....it is that easy to confirm... Quote
Jerry Roberts Posted March 30, 2017 Report Posted March 30, 2017 If you haven't done it already , that the coil out of the holder and see if there is any printing on it . Such as ' external resistor required ' . Quote
bambamshere Posted March 30, 2017 Author Report Posted March 30, 2017 Ok so took a look at truck and see ohms then I looked at it again and noticed that the positive wire for the coil goes right to the distributor. There is no resistor on this engine not sure if I should install one or not. Quote
bambamshere Posted March 30, 2017 Author Report Posted March 30, 2017 I had it out of the holder earlier and the only thing on it is the makers sticker and 12v Quote
bambamshere Posted March 30, 2017 Author Report Posted March 30, 2017 Omg I live in Canada not sure what it like where you guys are but a set of 8.5mm sparkplug wires here are 142$ up to 300$ ouch Quote
Plymouthy Adams Posted March 30, 2017 Report Posted March 30, 2017 tell me, why do you need 8.5 MM wires on a standard coil....????? Quote
classiccarjack Posted March 30, 2017 Report Posted March 30, 2017 (edited) 7MM is all you need. 8.5 MM is for systems producing 100,000 Volts + of spark. Like a race car or a later high power ignition system aided with a MSD or something comparable... I was able to get 6000+ RPM's out of my small block powered 1959 Dodge using 7MM wires, a ACCEL super coil, and good ol' factory Mopar points. I really can't fathom the need for 8.5MM wires on a flathead.... I modify every engine I own, and I only used 8.5MM on my old race car. But we can only give advice. It's your car.... Edited March 30, 2017 by classiccarjack Quote
bambamshere Posted March 30, 2017 Author Report Posted March 30, 2017 I probably don't but thats all they sell here for that year. I guess I could go a couple years a head of mine and see if I can get some. Maybe go to rock auto and see. Plus just wondering does anyone no how big a TX 315 engine I have googled it a veiw times and can't find anything. Quote
B-Watson Posted March 31, 2017 Report Posted March 31, 2017 The TX315 engine is 250.6-cid flathead six. Puts out 118 bhp at 3600 rpm. It was used in models FO-4 (1951-1952) and FP-4 (1953) 2 ton Fargo trucks. Bill Vancouver, BC Quote
bambamshere Posted March 31, 2017 Author Report Posted March 31, 2017 Thanks B - Watson appreciate it Quote
Phil Martin Posted April 2, 2017 Report Posted April 2, 2017 my 50 dodge is 12 volts. I have a resistor and was still going thru points like crazy. I tested and was getting 10 volts from resistor to dist. I switched the wires around on resistor and now get 6 volts to dist.guy tell me resistror is the same either way but this is the way it tests. Car is running way better and points haven't burnt out since I did it. Quote
maok Posted April 2, 2017 Report Posted April 2, 2017 2 hours ago, Phil Martin said: my 50 dodge is 12 volts. I have a resistor and was still going thru points like crazy. I tested and was getting 10 volts from resistor to dist. I switched the wires around on resistor and now get 6 volts to dist.guy tell me resistror is the same either way but this is the way it tests. Car is running way better and points haven't burnt out since I did it. Your dist.guy is correct, resistors don't have a polarity. You may have had loose connections. Quote
bambamshere Posted April 2, 2017 Author Report Posted April 2, 2017 K so I bought a resistor and 12v coil today. Now all I need is to find a diagram of how to install the resistor. Ther is a bunch on 2 wire distributors but I only have 1 coming out of my distributor. Quote
maok Posted April 2, 2017 Report Posted April 2, 2017 The resistor goes inline before the +ve of the coil for a -ve ground system (unless you have +ve ground setup) then the -ve of the coil goes to the distributor. Quote
meadowbrook Posted April 2, 2017 Report Posted April 2, 2017 On 3/29/2017 at 6:21 PM, Plymouthy Adams said: read the primary circuit ohm rating and see if it is an internal resistor coil. Many folks use these for the simplicity of not mounting an external resistor and a by pass wire to start on 12 and run on 6 but they do it at the expense of their points. The internal resistor coils keep a higher voltage for a longer period of time over the "switched" circuit that is the external resistor... if you primary is rough 3.2 ohms...you internal resistor.. rule of thumb on the external if you not racing and full saturation at x-rpm is not critical...is that the dropping resistor should be that of the coil's primary resistance... Excellent advice. A question, though, on a coil with an internal resistor, I suppose there is no way to run it without the resistor at startup like on the systems with an external resistor, correct? My neighbor has an 80s Jeep Wagoneer and he was having an issue of the vehicle starting but then stalling as soon as he released the key. Sounded to me like he had a problem with the ballast resistor, which in his case was a resistor wire. The kicker was, his vehicle had electronic ignition. Why would you need a ballast wire in a car with no points? All I can think is a legacy component, AMC Just never bothered to change the wiring when they converted to electronic ignition. Which was a Ford unit, I think. Quote
Plymouthy Adams Posted April 2, 2017 Report Posted April 2, 2017 coils needs the lower voltage to prevent overheating..the coil did not change with the swap to 12 volt...the resistor was added...the gauge circuits stayed the same only a CVR was added to keep them operational with the 12 volt supply. The internal resisted coil is not an item you can just by-pass the resistor inside due to its construction. Dropping resistors and means of resistance has changed over the years and vary with maker...you need to know if the supply wire to the coil is standard or of special high resistance wire before adding a resistor or you will end up with too much resistance in the circuit. One cannot just assume anything these days when buying a car especially of any age and possible modifications over the years. The means to determine the system is so easy with a volt-ohm meter...even our gal Ma Mopar will throw you a curve ball in the early days when it came to dropping the voltage... Quote
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