TFI 12v wiring question

[vacaisle]

I've been reading over this post and I have a question. How do you wire the ballast resistor? I see in the picture on that post that the resistor comes from a red wire that leads into the harness. On the oljeep diagram for an 88 the resistor splits off the hot lead to the coil. That's how mine is. So of I were to install a relay for a full 12v to the coil and use the original resistive wire as power to the relay, how do I wire the resistor? Does it just splice into the new hot from the new relay then get connected to ground?

[tgreese]

Why would you put the resistor to the relay coil? Are you meaning the magnetic coil in the relay, or the ignition coil?

Also, why are you adding a relay? You don't need one.

The ballast resistor limits current to the ignition coil. This is Ohm's law. It needs to be in series with the ignition coil primary. The ignition module provides the on-off ground for the ignition coil, just like the points (Kettering trigger) did on the old points distributor.

The TFI coil can possibly handle being shorted directly from 12V to ground, as if the ballast resistor was not there. However, the control unit was never designed to handle that much current, so it likely needs the ballast resistor. Usually the ballast resistor is between the coil 12V source and the primary winding of the ignition coil. Its purpose it to limit current, and thereby to limit power dissipation (heat) in the coil and the ignition module.

[vacaisle]

I'm just doing what rich88 did in the linked post from my original post. I want to give the ignition coil (TFI coil) full voltage. He used a relay powered by the original ignition coil 8.8v wire to send 12v to the TFI coil. The thing I'm talking about can be seen at D-3 in this diagram. Here it's called a noise suppressor. It's the schematic symbol for a capacitor. So I'm not sure exactly what it is. I've heard it called a ballast resistor. It splices in off the yellow wire currently going to my TFI ignition coil and then is grounded to the bracket that holds the coil. I want to know what to do with it if I do what rich did in his thread about this. He doesn't mention how that was integrated. This thread.

[tgreese]

The noise suppressor IS a capacitor. It does nothing but suppress ignition noise so noise does not show up in your radio. It does not conduct DC electricity, only electricity at radio frequencies. Has nothing to do with the ballast resistor. Remove it, ignore it, your choice.

The ballast resistor is the resistance wire near the ignition coil. It has to be there.

Rich88 has his own reasons for adding a relay. IMO it's just extra stuff that's not needed. It will not make any difference in the operation of the ignition. The ballast resistor does not limit voltage. Instead, it limits current. It's Ohm's law in the time domain. You can take my word for it, or you can read/study about RL circuits and understand it that way.

If you want to install the TFI coil, just remove the factory coil and replace it with the TFI coil. If you want to run the TFI coil without the ballast resistor, I suggest you replace your ignition module with the GM HEI module, then replace that resistance wire with a simple piece of wire. The GM module is designed to handle the current in a circuit with that style coil and no ballast resistor. Mount the module on a hefty heat sink.

I'm sorry if I sound a little strained in discussing this ...

[joe]

If you want 12v to the coil all the time what's the reason for a resistor (ballast or res wire)? Don't know what Rich did or why. Relays are just aux switches to route high current draw items (starter,lights, horn etc) so you don't run the big current through the stock switch circuit. If your coil needs a dropped voltage in the run mode to keep it from cooking put the resistor in the run circuit from the ign switch and use full 12v power to the coil for starting.
PS: capacitors/condensors are not resistors. Those condensors you see mounted to a coil are used as noise suppressors but unless you're having noise issues in your radio reception you don't need one. If needed using a resistor be it old school ballast or new age resistor wire just wire it in the "run/on" circuit leaving full 12v to the coil in the "start" circuit. The rating of the resistor is dependent on what operating voltage the coil requires. If you know the TFI coil needs 12v in the run mode(I don't know) than just wire it up like stock and just leave out the resistor. I try not to make electrickery any harder than need be. Solid, safe and adequate is good enough for me. Oh and please don't try to explain to me why you think you need a relay to run the coil. Not that I wouldn't be grateful, it's just that I know I won't get it.

[vacaisle]

Thanks for clearing that up. I was under the impression the capacitor was a ballast resistor but the resistance is in the wire. My mistake.

[vacaisle]

Today I hooked up the TFI coil the same way rich88 did in a post he made using a relay. It worked except when I turned the key to off the engine stayed on. Puzzling? So I ripped into the wiring harness, traced the resistance wire and took it out. I put a piece of regular wire in its place. So no relay. Just hooked up like its always been but with a regular wire in place of the resistor wire. Again when I turned the key to off it kept running. I put the resistor wire back and it shuts off like normal. I think it's continuing to run off the battery when I shut it off with no resistor wire. Maybe one of the electronics geniuses here can explain to me how the resistor wire prevents this from happening. I'm totally confused.

[tgreese]

Today I hooked up the TFI coil the same way rich88 did in a post he made using a relay. It worked except when I turned the key to off the engine stayed on. Puzzling? So I ripped into the wiring harness, traced the resistance wire and took it out. I put a piece of regular wire in its place. So no relay. Just hooked up like its always been but with a regular wire in place of the resistor wire. Again when I turned the key to off it kept running. I put the resistor wire back and it shuts off like normal. I think it's continuing to run off the battery when I shut it off with no resistor wire. Maybe one of the electronics geniuses here can explain to me how the resistor wire prevents this from happening. I'm totally confused.

Did you remove the ignition resistance wire or the alternator resistance wire? You need a resistance between the alternator and the ignition switch, so that the alternator does not backfeed into the ignition when the engine is running and the key is off.

If it dies when you unplug the alternator, it's backfeeding. You can replace the alternator resistance wire with a diode.

IMO you don't want to run the Motorcraft ignition module without a ballast resistor. It's not designed to sink that much current.

[vacaisle]

Did you remove the ignition resistance wire or the alternator resistance wire? You need a resistance between the alternator and the ignition switch, so that the alternator does not backfeed into the ignition when the engine is running and the key is off.

Yes. I removed the resistance wire between the alternator and the ignition switch. That's what was going on. I've been looking at an 88' wiring diagram and just spent some time studying an 86' diagram and figured that out. I think somebody in the past replaced my 89' harness with an 86' unless I have an 86' and the guy I bought it from thought it was an 89'.

IMO you don't want to run the Motorcraft ignition module without a ballast resistor. It's not designed to sink that much current.

There is some debate about that. I'd like to try it with full voltage. I would replace the ignition resistance wire right? On my truck it's pink with a light green trace.

[tgreese]

Can't help with the color code. You can read the diagrams as well as I can.

The resistance is between the +12V source (igniton switch RUN position) and the (+) side of the ignition coil.

[itselliot]

copied and pasted from another site

you need a diode at the alternator(brown skinny wire) to prevent voltage feedback that keeps ignition running

http://home.comcast.net/~amc_jeep/TFI.htm

http://home.comcast.net/~amc_jeep/HEI_relay.pdf

A Diode is a one way valve for electricity, so it has a flow direction that has to be observed.

If you want an easy fix, make sure the stripe of the diode is facing the alternator.
If I were you, I'd disconnect the Brown resistor wire all together, and run a wire from what used to be the positive side of your ignition coil connector...
(where the small Red MSD wire connects now)
And run that over to the alternator.
I'd put a Diode inline, with the stripe facing the alternator, and connect the other end of the diode to the #1 terminal of your alternator.

If you really want to get jiggy with it, use a new alternator plug (available from any discount auto parts store for around $4.).
The large wire (#2 terminal) will connect directly to the 'BATT' terminal on the back of the alternator. Use an 'Eye' connector, and have at it.

Connect a Radio Shack Diode (P/N 276-1143 or P/N 276-1144) with the stripe end facing the alternator to the small (usually white #1 terminal) wire.
The wire from the Positive side of the factory ignition coil connector will connect to the other side of the Diode.

If you want to do it the easy way, try Radio Shack P/N 64-3036A butt connectors for really small wire. These make the job a snap!

[vacaisle]

you need a diode at the alternator(brown skinny wire) to prevent voltage feedback that keeps ignition running

http://home.comcast.net/~amc_jeep/TFI.htm

http://home.comcast.net/~amc_jeep/HEI_relay.pdf

A Diode is a one way valve for electricity, so it has a flow direction that has to be observed.

If you want an easy fix, make sure the stripe of the diode is facing the alternator.
If I were you, I'd disconnect the Brown resistor wire all together, and run a wire from what used to be the positive side of your ignition coil connector...
(where the small Red MSD wire connects now)
And run that over to the alternator.
I'd put a Diode inline, with the stripe facing the alternator, and connect the other end of the diode to the #1 terminal of your alternator.

If you really want to get jiggy with it, use a new alternator plug (available from any discount auto parts store for around $4.).
The large wire (#2 terminal) will connect directly to the 'BATT' terminal on the back of the alternator. Use an 'Eye' connector, and have at it.

Connect a Radio Shack Diode (P/N 276-1143 or P/N 276-1144) with the stripe end facing the alternator to the small (usually white #1 terminal) wire.
The wire from the Positive side of the factory ignition coil connector will connect to the other side of the Diode.

If you want to do it the easy way, try Radio Shack P/N 64-3036A butt connectors for really small wire. These make the job a snap!

Thanks for that info. I've been talking with serehill off list about the exact same thing. I'm going to give it a shot tomorrow afternoon. I was contemplating removing the resistor wires but I don't want to make this more time consuming than it needs tp be. That would mean ripping into the wiring again. Maybe I will maybe I won't. If I do I'd remove both resistor wires.

[Gambler68]

Did you remove the ignition resistance wire or the alternator resistance wire? You need a resistance between the alternator and the ignition switch, so that the alternator does not backfeed into the ignition when the engine is running and the key is off.

If it dies when you unplug the alternator, it's backfeeding. You can replace the alternator resistance wire with a diode.

IMO you don't want to run the Motorcraft ignition module without a ballast resistor. It's not designed to sink that much current.

you NEED a ballast resistor. We proved this by melting two modules in a row this summer (wells lasted 3 minutes..Motorcraft about 1/2 hour.

[vacaisle]

you NEED a ballast resistor. We proved this by melting two modules in a row this summer (wells lasted 3 minutes..Motorcraft about 1/2 hour.

Yeah I figured that. The resistor wire connects to a yellow wire that goes directly to the ign module. The other ign module wire splices off the starter relay. I think I'll leave the alternator resistor wire in place and just add the diode and new coil relay idea.

[vacaisle]

Installed the diode right after the #1 terminal off the alternator. Shuts off great now. Also full voltage via the relay revealed a little more umph and less throttle necessary from a stop. Next step is a MSD 6a box. I guess I'm half way there with the relay.