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TR.....Wiring diagram?

632 Views 4 Replies 2 Participants Last post by  **DONOTDELETE**
Hey, TR just a quick question. is the wiring diagram you posted for the 258 or
amc v8, or are they the same? thanks, Ben

86 CJ7 258, weber carb, rusty but trusty!!
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They are the same.
If you are wiring something that did NOT have a Motorcraft ignition, you will need the resistor...

If you are wiring something from scratch, and you want to use the Motorcraft ignition, you will need the resistor.

If you are upgrading something that had a Delco breaker point ignition, you will need to remove the factory resistor, and place one of the recommended resistors in it's place.

If you are just doing the TFI coil upgrade, and using the factory wiring, and you already had the Motorcraft ignition system, you do NOT have to use a resistor... There is already one in place...

If you have your wiring harness apart, and your Jeep is more than 15 years old, it's a real good idea to go ahead and replace the resistor wire, just because of age alone...
If I didn't have the wiring harness apart, I wouldn't worry about it...

Attached is the diagram again....

"I Have The Body Of A God... Buddha"


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I'm a little bit confused about this resistor stuff. Is this resistor dropping the voltage below 12 volts or is it just changing the resistance and staying at 12 volts. Your long write up from last week says that the TFI coil requires 12 volts, but this shows a resistor going in place, which I have always understood to drop the voltage below 12 volts. If this is the case, the two posts contradict each other. If it's not the case, I am missing something (most likely).

The RESISTOR in the diagram is not needed if you have a stock wiring harness 78 to 90.
This diagram is for someone building a wiring harness from scratch...
Like someone rewiring your own jeep.

The resistor is already included in stock wiring harnesses, 78 to 90.
You just don't see the resistor, because it's a resistor wire included in the stock wiring harness.

When I started with this upgrade stuff back in January, we had all of these questions then,
But back then it was people telling me how stupid I was...

A resistor IS NOT a voltage dropping or voltage limiting device.
A resistor is a CURRENT choke.
Current is voltage and amperage together...
This is the simplest explanation I can think of...

If you check the voltage at the coil with the key on, and the engine not running, you should show very close to battery voltage.
When you start the engine, you start to use current (voltage & amperage).
The resistor just slows things down a bit... Like a restriction on a water line.

The entire load of the ignition coil grounds through the DuraSpark module.
The average ignition coil can draw up to 30 amps.
The TFI coil can draw up to 50 amps.
If you try to run 30 to 50 amps directly through the DuraSpark module, you will kill it in short order.
The resistor just chokes things down so the entire load of the coil is kept around 10 amps or so...

With out getting into textbook descriptions, that's as simple as I can make it.

I'm a tech geek, and I don't always know how to explain it for normal people.

"I Have The Body Of A God... Buddha"
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Thanks Aaron,
It was clear as mud before and now its....crystal!

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