Ignition Voltage
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Joined: Aug 2010
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From: Pleasanton
Ignition Voltage
So i've got an electrical issue that has me completely stumped. I recently installed a 21 circuit EZ wiring harness in my 64 f100. it has a swapped 352 and a new alternator. Everything else works perfectly, except for some reason i'm getting 17-18 volts at the input (+ terminal) on the ignition coil while running. I've checked the battery, and it has 13v while running which I believe indicates the alternator is charging correctly. However I have no idea where the 17 volts is coming from. I was under the impression that while running, the coil should be getting like 6-7. I haven't run the truck long, because i'm afraid of burning up the coil (yes it is a new coil), but at this point i'm not really sure what to do. Shouldn't the pink resistor wire be stepping down the voltage? Do i need to add in a ballast resistor as well? If so, how do i figure out what ohm resistor I need?
Cargo Master
Joined: Jul 2006
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From: Concord, CA
Missing info. Are you running points or electronic? Is it a stock coil or higher rated aftermarket?
A stock Ford coil cannot take that much current running through it particularly at low rpm's. They handle around 6V in run and around 10-11V in start. They do need an external resistor.
This new EZ wiring you have does it have a resistance wire at the ignition switch? If not then you need to add a ballast resistor to the circuit to lower the voltage. A ballast resistor around 1.35 ohms at a minimum. The higher the resistance the lower your voltage will be.
This assuming you have a stock setup with no resistor wire. To check put the key in the on position and check the voltage. If between 11-13V then no resistance, but if under 10V there is a resistance wire. At high rpm of 3,000 and producing more than 14V then you either need a ballast, or a coil with 3.5 ohm internal resistance, or a new voltage regulator.
So how is the voltage regulator?
A stock Ford coil cannot take that much current running through it particularly at low rpm's. They handle around 6V in run and around 10-11V in start. They do need an external resistor.
This new EZ wiring you have does it have a resistance wire at the ignition switch? If not then you need to add a ballast resistor to the circuit to lower the voltage. A ballast resistor around 1.35 ohms at a minimum. The higher the resistance the lower your voltage will be.
This assuming you have a stock setup with no resistor wire. To check put the key in the on position and check the voltage. If between 11-13V then no resistance, but if under 10V there is a resistance wire. At high rpm of 3,000 and producing more than 14V then you either need a ballast, or a coil with 3.5 ohm internal resistance, or a new voltage regulator.
So how is the voltage regulator?
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From: Pleasanton
thanks for the reply.
i am running points right now, but am planning on switching to electronic as soon as i get this sorted out.
it is only a stock coil, and not rated for voltage this high. the ez wiring harness does have a resistance wire running to the ignition switch, but it doesn't seem to be working.
I'm wondering if somehow I wired the alternator to the resistance wire along with the battery. i can't think of any other way that I would have voltage this high.
going to do some more wire-chasing tomorrow.
i am running points right now, but am planning on switching to electronic as soon as i get this sorted out.
it is only a stock coil, and not rated for voltage this high. the ez wiring harness does have a resistance wire running to the ignition switch, but it doesn't seem to be working.
I'm wondering if somehow I wired the alternator to the resistance wire along with the battery. i can't think of any other way that I would have voltage this high.
going to do some more wire-chasing tomorrow.
Elder User
Joined: Jun 2012
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To get 17 volts you have to have the battery in series with the alternator output somehow..... these systems should always be hooked up in parallell.
I have never seen it but perhaps your are getting 12 volts from the battery in series with 6 volts from the alt. circuit..... May be possible if your alternator system negative is hooked to the pos of the battery circuit with the neg of the alternator sysem at ground..... wierd
Check your meter or your eye glasses.
A runaway alternator with a bad regulator should not give you 17 volts.
By the way, if the diodes are bad in the alternator.... no telling where the electrons are going...
6 volts would be correct down stream of a high resistant ballast resistor after it is warmed up.
I would start the engine and have someone quickly disconnect the battery and then test voltages.
I have never seen it but perhaps your are getting 12 volts from the battery in series with 6 volts from the alt. circuit..... May be possible if your alternator system negative is hooked to the pos of the battery circuit with the neg of the alternator sysem at ground..... wierd
Check your meter or your eye glasses.
A runaway alternator with a bad regulator should not give you 17 volts. By the way, if the diodes are bad in the alternator.... no telling where the electrons are going...
6 volts would be correct down stream of a high resistant ballast resistor after it is warmed up.
I would start the engine and have someone quickly disconnect the battery and then test voltages.
Posting Guru
Joined: Mar 2006
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Why not?
I was helping a buddy wire a Delco into his Plymouth. I had a meter on it. When he fired it up, it hit 17 volts, and i told him to shut it down, assuming it was a bad regulator.
Elder User
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I was thinking about speed vice voltage, regardless of the speed or frequency, the diodes (if not burned out) will provide dc current. Thanks for the catch.
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From: Pleasanton
ahh shoot. i got carried away working on my slick and forgot to reply. I got the problem fixed, and wanted to say thank you for the help. it turned out the wire to the coil was not a resistor wire (i thought it was), and all i did was install a ballast resistor, which gave me the correct 12V to the coil. that, and a freshly installed pertronix electronic ignition conversion, and she runs very smooth now.
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Posting Guru
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ahh shoot. i got carried away working on my slick and forgot to reply. I got the problem fixed, and wanted to say thank you for the help. it turned out the wire to the coil was not a resistor wire (i thought it was), and all i did was install a ballast resistor, which gave me the correct 12V to the coil. that, and a freshly installed pertronix electronic ignition conversion, and she runs very smooth now.
the resistor is supposed to take you from battery voltage (about 13-14v with the engine running) down to 6-9v.
the idea that you have 17 volts *anywhere* in the system means that something is wrong. to me, at least-
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From: tujunga, calif
I have to agree with Rustywheel, something isn't right. Just think, all the lights, accessories etc. are designed to work on about 14V max. You may end up frying a few things eventually. Are you sure your meter is reading accurately? Maybe test it on something else.
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Anybody have an idea how to check the electronic ignition system in my econoline 100 which I switched out engines, used the same distributor, coil and everything in fact but now I have no spark to plugs. I am lost how to start. The coil has 12v with the key on. It almost looks like the original '79 engine had points and this is aftermarket electronic. The four inch square box has two pig tails coming out, one with three wires and the other with four. The four wires seem to have some of the same colors to match dist. but the voltage on them all is very low. If I have a bad ground, which seems quite likely...any idea how to make sure the correct wires are grounded? Thanks from the deep Midwest, in the middle of nowhere USA.
Elder User
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So, how is Kansas?
Those darn boxes with wires sticking out can be tricky with a good set of instructions, a nightmare without because you can easily burn one out.
To get help on this, post the mfg. and any data listed on the item(s) in qustion. A picture and the color of wires will help. If no one can help here, try to go on line or to a parts store, search for one like it and get the instructions. Good luck.
Those darn boxes with wires sticking out can be tricky with a good set of instructions, a nightmare without because you can easily burn one out.
To get help on this, post the mfg. and any data listed on the item(s) in qustion. A picture and the color of wires will help. If no one can help here, try to go on line or to a parts store, search for one like it and get the instructions. Good luck.
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Electronic Ignitiion trouble
Thank you for the reply. I will get a picture. The aluminum box has no markings on it, so adds to the fun. As I broke the plug connection when removing the original engine, with the three wires coming out of the distributor - then I am pretty sure I didn't put them back correctly the first time I am afraid I did fry something already. I should have cleaned the wires off to see the coloring, eh? Kansas, South Dakota - North Dakota...same thing...government subsidized corn for miles around and hard to find real gas without alcohol added.
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