Do I really need a ballast risistor?

[Slow Poke]

I just switched over to a points/condenser distributor from City Racer. The truck runs so much better since I made the change with one exception. It’s difficult to start now. Warm or cold, it makes no difference. If I bypass the resistor however it starts immediately. I don’t even touch the gas pedal. Half a crank and it’s idling. I measured the voltage on the + side of the coil with the resistor in place and I get 11.5 and 6.9 at the - side. Without the resistor I get 14.5 + and 7.5 - I have a coil that says it has an internal resistor that I swapped in and I got similar numbers as the new coil. 14.5 + and 7.0 - I’m not sure if this means my new coil has an internal resistor or if the old coil is just acting weird. In either case though, I still only have 7 or 7.5 volts at the - post on the coils. Does that mean I don’t need the resistor?

 

[Slow Poke]

I just switched over to a points/condenser distributor from City Racer. The truck runs so much better since I made the change with one exception. It’s difficult to start now. Warm or cold, it makes no difference. If I bypass the resistor however it starts immediately. I don’t even touch the gas pedal. Half a crank and it’s idling. I measured the voltage on the + side of the coil with the resistor in place and I get 11.5 and 6.9 at the - side. Without the resistor I get 14.5 + and 7.5 - I have a coil that says it has an internal resistor that I swapped in and I got similar numbers as the new coil. 14.5 + and 7.0 - I’m not sure if this means my new coil has an internal resistor or if the old coil is just acting weird. In either case though, I still only have 7 or 7.5 volts at the - post on the coils. Does that mean I don’t need the resistor?

I did some more research and found this.
Both Ohm out very similarly as being the internal resistor type. So unless I’ve got this wrong I’ll remove the resistor. Worst case scenario I burn up a set of points

 

[CruiserInProgress]

I can't comment on your internal resistor coil question, but if you have points or had an early oem electronic ignition, you may want to run with a ballast resistor or a resistor wire.

Earlier ignition systems use a ballast resistor to limit the continuous voltage (running down the road) to the coil + to 7v or so. Later electronic ignition systems (like used with the oem big cap) don't have that requirement.

Not sure if this applies to your setup, but my 79 had a "cold start" circuit that allowed for full battery voltage (12 to 14v) at coil + only while cranking, then dropped back to 7v when running.

The "cold start" circuit uses the oem starter to create a switched connection from the positive starter cable to the coil +, while cranking only.

You might check the schematic for your year to see if you should have that circuit.

 

[pb4ugo]

Here ya go.

Thread 'Switching to a coil with an internal ballast resistor'

Aug 25, 2023

I am starting an FJ45 project and there is a coil with an external ballast resistor. I am thinking of getting a new coil with an internal resistor… not being well schooled in ignitions, what happens to the two wire that are connected to the external ballast resistor right now?

• knuckle47
• coil ignition resistor
• Replies: 10
• Forum: 40- / 55-Series Tech

 

[charliemeyer007]

I'm going to add a switched circuit to power the coil from the battery directly for starting and put the resistor in line with the regular ignition with my new Amoron coil/resistor unit. I have a chineesium deloc dizzy.

 

[3_puppies]

IIRC when starting the resistor is bypassed, and gets 12V+ to the coil side of the resistor
then when key in run position the +v goes thru the resistor to cut the voltage down so the coil survives

I had a guy stop by years ago and he had trouble starting his rig, crank and crank then let off crank and the rig would start, found he wasn't getting voltage to the coil during crank only in run position, ran a bypass wire and it started right up with minimal crank, he fixed it when he got home.

 

[fjwagon]

What 3_puppies said. The idea for ballast resistor is to keep the coil from over heating. So theoretically, the ballast is stepping down the 12v to 7 to 8 around 9v depending on the incoming voltage and the value of the ballast resistor. Basically operating voltage should not be 12v regardless if you use a coil without a resistor in series. After the engine starts you want to see around 7-8v at the coil under normal circumstances. To be more precise check the voltage before it goes to the ballast resistor. Ohm out the the resistor. And with your trusty OEM should figure out if you are with in tolerance. If interested, divide the voltage with the ohm reading you got and it should give the voltage drop. I'm seen people remove the ballast resistor when they install a Petronic set up. But I'm guessing they probably also change the coil to a coil with an inernal resistor. Worse case, call the vendor for technical support.

 

[charliemeyer007]

I think its more about making the points last longer, by using a resistor to drop the voltage. Bypass the resistor the points die within 5000 miles - the coil soldier's on. Only my experience YMMV

 

[fjwagon]

You are probably right Charlie, the arcing at higher voltage definitely shortens the life. Heat is the worst enemy in electronics. If can keep cool it will last a long time.

 

[B y r o n]

If the coil has a resistor built in you do not need an external resistor.

 

[anothernz45]

But it will start better with an external resistor and normal coil

 

[Slow Poke]

When I asked about installation instructions from City Racer they sent me this. If the points burn up quickly my plan is to put the resistor back in and install a relay from the start circuit of the ignition switch to bring full power to the + side of the coil at start up. Hopefully I’m good as is but there’s another set of points in the glove box in case plan A goes sideways

 

[pb4ugo]

When I asked about installation instructions from City Racer they sent me this. If the points burn up quickly my plan is to put the resistor back in and install a relay from the start circuit of the ignition switch to bring full power to the + side of the coil at start up. Hopefully I’m good as is but there’s another set of points in the glove box in case plan A goes sideways

View attachment 4070655

Did you read the link I posted? As Bryon mentioned, If the coil has an internal resistor, you shouldn't run a ballast resistor. If the coil doesn’t have an internal resistor you have to run a ballast resistor.

 

[aztoyman]

Don't forget to make sure you never leave the ignition key on with points ignition. Not really a problem if the engine stops with the points open. But if the points are closed, it can over heat your points, coil and wiring. It can potentially burn more than just your points. AND it's a parasitic drain on your battery.

 

[anothernz45]

You may not need a relay, have a look at your starter motor solenoid and if there's a terminal there doing nothing use that. It's live when the starter is going

 

[rlong]

Don't forget to make sure you never leave the ignition key on with points ignition. Not really a problem if the engine stops with the points open. But if the points are closed, it can over heat your points, coil and wiring. It can potentially burn more than just your points. AND it's a parasitic drain on your battery.

I had a coil explode in my 40 or 45 years ago leaving the key on (and points coincidently closed); blew the "top" out! (bottom as mounted on F motor) I was working in the shop so was there to hear/see it, touched it and it was hotter than s@#%. It was as impressive as it was annoying, I had no money for parts at the time.

 

[numby]

You may not need a relay, have a look at your starter motor solenoid and if there's a terminal there doing nothing use that. It's live when the starter is going

This...

Looks like '77 models have a bypass. Look at the first image for 1977 FJ40 on Coolerman's website.

https://globalsoftware-inc.com/coolerman/fj40/schematics/FJ40/1978FJ40/1978fj40_wiring_diagram.pdf

EDIT: Adding in here...

Notice the Blk/Yel wire from the IGN switch runs to the ballast resistor and then to the coil. That is the "RUN" circuit. The Blk/Wht wire from the IGN switch is the start line. It runs directly to the solenoid on the starter which sends full battery power to the coil bypassing the ballast resistor. Some years have a resisted line from the IGN switch to the coil that takes the place of the BR.