Coil will not fire

I am trying to chase down a problem of no spark in a Fcub (six volt + ground system). I cannot get the coil to fire. Neither the new one or the old one. There is six volts on the -side of the coil and I am using a starter (hot wire) switch to ground the + coil primary. You can see on the tractor amp meter that there is good current draw on grounding the coil . On the HV side I have inserted a spark tester and attached this to a ground. Opening and closing the primary switch is not giving me a spark. I have already replaced the ignition switch because it was displaying high resistance due to a low voltage on the battery side of the coil ( as low as 3.5 volts ) when grounded. Now when the coil is grounded the voltage stays around 6 volts. Am I testing this coil properly? Is it possible that the battery has too much resistance? I sort think not due to the size of the deflection on the amp meter.

The big difference between the old coil and the new coil is the primary resistance. The old was about 22 ohms and the new is about 1.7 ohms. The old has 10.5 Kohm from HV out to the primary coil and could not measure ohms to case due rubber coating on case. The new has a metal case and gives 8.5 Kohms from HV out to primary coil and is open to case.

Any advice would be appreciated.

A coil is just one part of many parts to an ignition system. You need to have a good ignition switch a good condenser and good points and in this case your problem is most likely bad or corroded points. I have yet to figure out why so many people throw new coils at a no spark problem when 95% of the time it is bad points and bad points equal NO SPARK

Put the coil on the tractor and test it under the conditions it will actually operate. Wire it up, turn the switch on, and open the points with a small brass rod (just kidding) and a spark should occur when the points are opened. When the points are closed, you should note a small discharge on the ammeter. If no discharge, the points are dirty or the primary circuit is open.

For a good spark, it needs the condenser in place. There are interactions between the condenser and the secondary that are important. When testing as you are, the wire tor the distributor must be disconnected. There needs to be a condenser from your grounding jumper, and ground as there is in the distributor. The coil case in not connected to the windings.
I bet your points need to be cleaned and the pass through connection checked for a contact to ground short.
Jim

YOUR STATEMENT

"There is six volts on the -side of the coil and I am using a starter (hot wire) switch to ground the + coil primary. You can see on the tractor amp meter that there is good current draw on grounding the coil"

MY RESPONSE

If its a correct and working typical 6 volt coil Id expect a current draw of around 3 to 4 amps if 6 volts is applied across its terminals


YOUR STATEMENT

"On the HV side I have inserted a spark tester and attached this to a ground. Opening and closing the primary switch is not giving me a spark."

MY RESPONSE

If the coil is good and youre testing it by manually applying but then removing voltage across its terminals, each time the voltage is removed (like points opening) a HV spark out the top HV tower terminal (using a plug wire) should easily jump a 3/16 or so gap to frame ground. That will happen regardless if you have a condensor in the circuit or not, although the spark would be greater if one were used


YOUR STATEMENT

I have already replaced the ignition switch because it was displaying high resistance due to a low voltage on the battery side of the coil ( as low as 3.5 volts ) when grounded. Now when the coil is grounded the voltage stays around 6 volts. Am I testing this coil properly? Is it possible that the battery has too much resistance? I sort think not due to the size of the deflection on the amp meter.

MY RESPONSE

Again a typical working 6 volt coil LV primary would draw around 3 to 4 amps and thats NOT enough current draw to drop the battery voltage (IFFFFF its a good and charged battery) anything significant. A high currrent starter motor draw can reduce battery voltage, but a 4 amp draw should drop battery voltage unless the battery is bad assuming all else and wiring is okay

YOUR STATEMENT

The big difference between the old coil and the new coil is the primary resistance. The old was about 22 ohms and the new is about 1.7 ohms.

MY RESPONSE

A typical 6 volt coil would have a LV primary resistance of maybe 1.2 to 2 ohms certainly NOTTTTTTTTTTT 22 ohms


I suggest you run my Ignition Troubleshooting Procedure below for a systematic approach to determine the cause of no spark, but a coil LV primary of 22 ohms sounds baddddddddd and so often the cause of no fire is the points are bad or pitted or burned or not gapped right or not closing. Next problem may be a weak (causes weak spark) or shorted (causes her not to fire) condensor

Check the points, run my procedure is my advice, let us know what you find

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T
John Ts Ignition troubleshooting

I have a 560 that cuts out after oreration. I have a resistor in the coil, but this is not working. Do I need a resistor besides the one in the coil?How would this be wired in?

If you X Ray or disect your 12 volt coil you likely will NOT find any discrete stand alone "resistor" hidden away somewhere inside the can, (still out of old habits or old wives tales many still refer to them as having a "resistor" inside) But no prob, people have a right to call them anything they darn well please despite whats really inside them!!!!!

Butttttttttt if you have a 12 volt tractor and your coil is labeled "12 volts" orrrrrrrrr "12 volts NOT for use with ballast" orrrrrrrrrrrr"12 volts no ballast required"

NO DO NOT ADD YET EVEN MORE EXTERNAL SERIES BALLAST OR THE SPARK WILL BE WEAK

On a 12 volt tractor if you have a 6 volt coil (or one labeled 12 volts requires ballast) then YES you need just what it says or the coil will overheat and the points will burn up much sooner

How to wire an external ballast you ask??? It wires in series between the ignition switch IGN output and the coils LV primary input.

ONCE MORE if its a 12 volt tractor you can use EITHER a "12 volt" coil or one labeled "12 volts NOT for use with ballast" buttttttttt if you use a 6 volt coil (or one labeled 12 volts requires ballast) then add the series ballast after the ign switch IGN output and before and ahead of the coils input so it drops 6 volts leaving 6 on the 6 volt coil as it was designed to handle WELL SHUCKY DERN

John T