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Coil question

2378 Views 1 Reply 2 Participants Last post by  Junk Yard Genius
I rebuilt the engine wire harness over the week-end,Putting every thing back where it was supposed to go.But now there is no fire from the coil.I've got 12 volts on both the positive and the negative posts on run and start.Is that right?The only wires attached to the coil are the tach and the ignition ground on the neg side and if I remember well one wire from the s side of the starter solenoid,This one I'm not sure I'm not under the hood!Idid up the gauge on all the wires(10ga for 12ga...)Help!It's a prestolite.

Ben (I want to get it to run before the ford duraspark mod)

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You just said 'Prestolite', so I don't know if you have the points Prestolite, or the electronic ignition Prestolite. (Presto!-it's junk!)

Where does your negative side of the coil wire go?
If you have 12V to the positive side of the coil during cranking, and while the key is in the 'RUN' position, and you have the ground to the coil going to the ignition module or breaker points, it sounds correct.
If anything is connected to the negative side of the coil except the module wiring or the breaker points lead, remove it during testing.
The lead from the starter 'I' terminal goes to the positive side of the coil.
(I hope I read your posting wrong, because if you connected a hot lead to the module wire, it stands a good chance of having fried the module.
Is your module getting power? It should be fed from the same circuit that feeds the positive side of the coil.
Most modules have just a few wires, on of them is the power feed.
(Some, like the DuraSpark module, have two power feeds, one for cranking, one for 'RUN'.)
One wire will go to the negative side of the coil to control the coil circuit.
One wire will ground the module. (some modules ground through the housing, so check your grounds)
One or two wires will go to the distributor pick up module.
That's about all there is to it.

Here are some tests...
1. Is there anything else connected to the negative side of the coil? If so, remove it for testing.
2. On many of the factory tachs, if the wires aren't plugged in, the ignition won't fire.
(Thank CJ Dave for that one, I forgot all about it.)
3. Ground a spark plug to something on the engine. Just wrap a wire around the threads of a spark plug, and ground the other end of the wire.
Then, plug the spark plug into the coil wire.
Turn the key on so the coil gets power.
Use a test light or volt meter to make sure the coil is getting juice.
Take the wire off of the negative side of the coil , and just touch it to the coil post several times... Are you getting sparks at the test plug? If not, the module or wiring harness is suspect...
4. Unhook anything going to the negative side of the coil.
Make sure the positive side of the coil is getting 12V.
Now, use a grounded wire and tap the negative side of the coil several times real fast... Any sparks?
If not, the coil is probably bad.
5. If you do get sparks on both tests, put everything back together except the test plug connected to the coil wire.
Hook nothing up to the negative side of the coil except the module or breaker points.
Turn the engine over.
Do you get sparks at the test plug?
If you do, it's something wrong with the distributor cap & rotor assembly, or the timing is so far off it won't run.
If you don't get spark at the test plug.... Looks like the module or wiring.
6. Take your control module somewhere to be tested.
7. Do the resistance test on the 'trigger' in the distributor, or check to make sure the points are working.

If it turns out the be the Prestolite ignition module...
This is a really good time to up grade to a DuraSpark ignition. If you send me an e-mail address I can send a fairly large file to, I'll send you step by step instructions for the upgrade.
The upgrade is easier than trying to fix this problem. If you have the 304/360 V-8, I have a distributor we are not using, and I will sell reasonable, or if you would rather, I can put the entire kit together for this upgrade. It's all off the shelf stuff, and not very expensive.
Looks like the entire upgrade, everything but spark plugs is about $275. if I do it as a kit.
You can knock $50 off if you have a Motorcraft distributor core for the 304/360.
This is for a recurved distributor to maximize performance, the module, the large cap assembly, plug wires, coil, connectors and instructions.
This system will whip the Prestolite's butt, and will slap the snot out of the GM HEI.
This is probably not an emissions legal upgrade in most states with tight emissions laws.
--If you just want the instructions with pictures and part numbers, that is free if you have an email address that can handle large files. If you are good with a wire crimper, soldering iron, and heat shrink tubing, this is the way to go.
You may look in the old postings, I have posted this upgrade several times.

Let me know what you think, or if you have any questions.
Later dude, Aaron.

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