Ballast Resistor??
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Junior User
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Ballast Resistor??
Previous owner(s) converted my '86 302 from TBI to 2bbl carb setup, I'm assuming Duraspark or a variation thereof. It cranks everytime, seems to run ok (minus choke/rich issues) but I want to clean up the hack job wiring they did. Obviously, the easy route is to hook it all back up like it is now. However, I've noticed several "extra wires" that go to nothing and that the ballast resistor has nothing connected to it. Since everything "works" should I leave well enough alone or is there a need to have the ballast connected?
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
What ballast resistor? There are some in these trucks but they aren't obvious, so I'm not convinced that what you are seeing is a ballast. How about posting some good pics of what you are talking about so we can all be on the same page?
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
None of us can answer the question, only you can. That's because we can't tell what they did. There is/was a ballast resistor in the original wiring, as shown on Page 29 here: Start & Ignition - Gary's Garagemahal. But we don't know if it still in use since someone changed things.
If you have factory-looking wiring, meaning they used a factory harness from a DS-II truck, then the ballast resistor should be in and working. But if they hacked it up, who knows? So, you need to test it. Put a voltmeter on the Batt terminal of the coil, where the W/LB and R/LB wires are in the drawing. With the key on and the engine not running you should have battery voltage. With the engine running you should see the voltage oscillate, and if you have an analog voltmeter it will probably be about 7 - 9 volts because the voltage is dropping across the ballast resistor when the coil is being charged. But, if you don't have a ballast resistor the voltage won't drop much and you'll see something close to battery voltage.
Another way to test is to put your volt meter as above, turn the key on, and ground the other terminal of the coil. Your meter should go from battery voltage to 7 - 9 volts when you do.
If you have factory-looking wiring, meaning they used a factory harness from a DS-II truck, then the ballast resistor should be in and working. But if they hacked it up, who knows? So, you need to test it. Put a voltmeter on the Batt terminal of the coil, where the W/LB and R/LB wires are in the drawing. With the key on and the engine not running you should have battery voltage. With the engine running you should see the voltage oscillate, and if you have an analog voltmeter it will probably be about 7 - 9 volts because the voltage is dropping across the ballast resistor when the coil is being charged. But, if you don't have a ballast resistor the voltage won't drop much and you'll see something close to battery voltage.
Another way to test is to put your volt meter as above, turn the key on, and ground the other terminal of the coil. Your meter should go from battery voltage to 7 - 9 volts when you do.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
True, Jim. But the inexpensive meters I've been around have a hard time telling a long piece of small wire from that 1 ohm "resistor". However, they are pretty good at seeing the voltage drop.
pedant
Joined: Jan 2008
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From: EXTREME southwest CT
Isn't it supposed to be 1.3 or 1.4 ohms?
I'd imagine you could see that, even with a test light.
Where you WON'T see it is reading the coil primary with the engine off.
There's just not enough load to drop the voltage with the coil saturated.
I'd imagine you could see that, even with a test light.
Where you WON'T see it is reading the coil primary with the engine off.
There's just not enough load to drop the voltage with the coil saturated.
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Junior User
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Ok, thanks. But to rephrase my initial question...what is the purpose of the ballast? To reduce coil voltage to 7-9vdc? Any harm in it not being in play, hypothetically speaking?
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pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
Harm will be done to both module and coil without it.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
Running w/o a ballast will do it. Jim - Bill's 1986 EVTM shows 1.1 ohm for both DS awa TFM. And, you know that I agree that the meter or even a test light won't drop the voltage enough to really tell when the engine is off.
Lead Driver
Joined: Nov 2013
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The coil is designed to run continuously on 8 volts (or whatever the actual value is, but it's less than the full 12 volts). During starting, the resistor is bypassed so the coil gets a full 12 volts for a short period and creates a hotter spark. It's not a problem to bump up the voltage to the coil during the short time the starter is engaged. If run continuously on 12 volts, "Harm will be done to both module and coil without it" (the ballast).
Hope this helps.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Yup. Another reason I asked for pics. We don't know what he has nor how it is wired. All we know is someone replaced EFI with a 2bbl and screwed on a Chrysler ballast resistor. Sure would help to see what is there.
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
in these trucks but they aren't obvious, so I'm not convinced that what you are seeing is a ballast. D7AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-213) / Obsolete ~ Available NOS & from auto parts stores.
49" long / Color coded red with green stripes / 1.30/1.40 ohms resistance / #16 gauge wire.
1977/89: F100/350, Bronco, Econoline & misc. Passenger Cars.
Pic: The Doubting Thomas' can scroll down to 12250