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John Deere Tractors Discussion Forum

Correct Ignition Coil for JD 730

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John

04-16-2004 07:33:56

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Does anyone have information giving the correct part number for a 12 volt coil for a 730. I am looking for a crossover number to Delco or other manufacturer. If not, will a universal coil from an autoparts house work OK?

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Clooney

04-16-2004 09:49:56

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Re: Correct Ignition Coil for JD 730 in reply to John, 04-16-2004 07:33:56

John, I don't have any of my coil data handy in the location I'm at now but your 730 [assuming it isn't a diesel] used a 6 volt coil [no internal resistor] & also used an external ballast type resistor up under the front of the IP panel.. The original coil was positive ground but most of the 6 volt aftermarket or Delco replacement coils will work fine at either polarity as long as the + terminal is hooked to the distributor.. Even if you have the correct original Delco coil number it has probably been superseded to a generic coil by now anyhow..

~Most of the early Deere [Delco] 6 volt coils had between about 1.1 & 1.4 ohms of primary resistance at room temperature so about all you need to do is find a 6 volt coil that measures in that area somewhere. The original Deere ballast resistors ran a little higher on resistance than the automotive replacement resistors so if you use an automotive 6 volt coil that has primary resistance in the 1.5 or higher resistance range you might also want to consider using a replacement ballast resistor from the auto parts store as those seem to run in the 1.5-1.8 ohm range & will better match the higher resistance coil..

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John T

04-16-2004 07:56:47

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Re: Correct Ignition Coil for JD 730 in reply to John, 04-16-2004 07:33:56

John, I dont have any Declo specs, but show the Coil's John Deere Part Number as AM 791-T (Coil & clamp). Yes, an automotive type coil would work, but remember, its a 6 volt coil (assuming youre wired usign the external ballast resistor circuit) if you try to buy an auto or generic substitute, many trucks/cars/autos up to into the fifties and earlier used 6 volt coils and often are labeled 6 Volts right on their case. Its DC resistance measured between its lil + and - terminals would be in the vicinity of 1.2 but under 2 ohms most likely, while a 12 volt coil is more like 2.5 to over 3 ohms. If you didnt have or abandoned the external ceramic bathtub type ballast resistor and by pass circuit and made some other wiring changes, an internally ballasted 12 volt coil could be made to work, but I would stay with the original 6 volt coil and ballast system.

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Good Luck n God Bless ya John

John T

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