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Coils and External Resistor

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I know this question has been asked before, but I can't find the answer to this question...

I have a '74 2002. There are two wires leading into a single female clip and attaching to the + side of the red coil I have. One of the wires is red/black. The other is a colorless, cracking non-descript wire. I am guessing that the second wire is the resistor wire they put in on later model '02s. Since the insulation is coming off, I am wondering how much good it is doing. I have a brand new external resistor I purchased from Ireland. Can I just cap off the second wire -- the one I think is the resistor wire -- and only connect the first to the resistor and then to the + side of the coil? Or does it need to be removed all together?

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No,

the red/black wire is needed to get full voltage while starting the car. this wire comes from the starter.

The resistor wire comes from the fuse block, I think fuse #11 or 12 and has about .9 ohms of resistance.

What ohm resistor did you buy from Jeff? If it's around 1.6-1.8 which is what the Red coil calls for, then you need to just buy a small roll of wire and run it from the fuse block to the external resistor and then from the other side of the resistor to the + side of the coil with the red/black wire.

If you use the resistor wire with your external resistor, you may end up with you much resistance going to the distributor. which will cut down on voltage.

The wires in the fuse block are connected via a female slip-on connector.

Ron

74tii

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Thanks for replying. I'm still a bit confused. If I am understanding you correctly, both of the wires are important.

The red black one should always go directly to the coil. THe other one, the one that looks like it's not a great wire should route through the resistor. Is this correct?

And here's maybe the crown jewel of dumb questions, what is the fuse block? You don't mean the fuse box do you?

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Need to find out what ohm external resistor you bought from Jeff.

Both wires are important. The black/red you do not want to touch, it supply's full voltage at cranking time and comes from the starter

With the red coil you need around 1.8 ohm resistance to the coil while running

This is because the starter no longer supplies current after the car starts.

If Jeff sold you a 1.8 ohm resistor, you need to bypass your clear .9 ohm wire that runs to the fuse box(sorry on the confusion). One way is to run a new wire from the fuse box to one side of your resistor, then from the other side of the resistor to your coil.

this is the wire that will then supply voltage to your coil to keep you running.

If you try to use the clear wire and the external resistor, you will have to much resistance. 1.8 ohm external resistor + .9 ohm wire = 2.7 ohms.

Unless Jeff sold you a external resistor with around .9 ohms of resistance, then .9 ohms from resistor + .9 ohms from your wire = 1.8 ohms which is need for the red coil

What I did with my red coil was to buy a 1.8 ohm external resistor, then ran a new wire from the fuse box to the resistor and from the resistor to the coil.

Also, Is the red coil new or having you always just been running the clear wire to the coil?

ron

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Okay...So it's a 1.8 ohm resistor.

I replaced the coil a while ago but was adivised by someone, can't remember who, that with an electronic ignition i need not worry about a resistor. But, what I've found is quite a bit of carbon buildup in the distributor cap. Spoke with Jeff about this and he said i need a resistor.

No problem so far. But then when I went to put it in and saw the shape of the clear wire, it made me wonder if that was the resitor wire mentioned in other posts as I was wondering if it could really be carrying a current very well. Which may in fact be part of the problem I've been having.

So is the clear wire than the one I would connect into the resistor and the red/black one go directly to the coil?

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If you have the 1.8 ohm resistor, don't use the clear wire, just bypass it all together.

run a new wire from your fuse box to the resistor, most wire has no resistance. So if you have about 5 foot of spare wire laying around use it or buy a small spool for Advance or Autozone.

I'm surprised you didn't burn your coil up just using the clear wire or burn up your electronic ignition

The difference come in depending on what coil you use.

With the red coil you need a 1.8 ohms.

With the Blue coil, no clear resistor wire or no external resistor because the coil has built in 3 ohm resistance.

With the black coil, it has .9 ohms which would have been original coil on your car and why you needed the clear wire

The clear wire in the fuse box use a female disconnect. Put a female disconnect on your new wire and plug it in where the clear wire was.

Basically, unscrew the on screw that holds the fuse box down and lift it up and look at the bottom, pull the clear wire off and replace it with your new wire. Or if you have to, cut the clear wire in the fuse box and splice your new wire to it.

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The "colorless" resistance wire does not originate in the fuse box. It is spliced to a green wire within the harness that runs across the firewall. See this post for complete details: http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/topic_view,threads/p,637995/t,327582/

If you want to replace your resistance wire with the external resistor, unplug the resistance wire from the coil + (15) terminal, and tape it up out of the way. Connect a piece of wire from the coil + terminal to one end of the new resistor. Connect a second piece of wire from the other end of the resistor to the splice described above.

If you don't want to connect to the splice within the harness, you can make the connection in the fuse box instead. I don't have the details of that handy, except that you're looking for a green wire.

Keep the red/black wire from the starter to the coil + terminal as is.

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FYI- On my 74 tii, the colorless wire did originate in the fuse box and plugged in either fuse 11 or 12. I only say that due to I had to unplug the wire from the fuse box, so I could run a non-resistor wire to my red coil.

Could the PO possibly made a change, I don't know, but seen diagrams that are one thing for a 74, but different on earlier and later models.

Good pictures in your DIY.

Ron

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Thanks everyone for the information. I just traced my resistance wire and low and behold it spliced into a green wire coming out of turn signal area. Fascinating.

So to be sure, what I want to do is disconnect this resistance wire. And splice in a new piece of wire -- standard copper I am assuming, solid or wound? -- and take this wire to one end of the resistor and from the other end of the resistor take a wire and go to + side of coil. Leave the red/black going directly to coil. Is this correct?

And I know that it wasn't good to run this with out the resistor. Is there anyway to tell if I did damage to my crane ignition? or the coil? Or do I assume I did and replace both of them?

Thanks again.

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Thanks everyone for the information. I just traced my resistance wire and low and behold it spliced into a green wire coming out of turn signal area. Fascinating.

So to be sure, what I want to do is disconnect this resistance wire. And splice in a new piece of wire -- standard copper I am assuming, solid or wound?

Wound

-- and take this wire to one end of the resistor and from the other end of the resistor take a wire and go to + side of coil. Leave the red/black going directly to coil. Is this correct?

Correct

And I know that it wasn't good to run this with out the resistor. Is there anyway to tell if I did damage to my crane ignition? or the coil? Or do I assume I did and replace both of them?

I think if she starts and you don't hear any type of missing sound, if you have good spark to each plug and it seems like your getting good power. I'd go with what you have.

Someone else may have a better way to tell if everything is ok or not.

good luck

Ron

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Thanks for the excellent info on the resistance wire in your '74 tii. The resistance wire in a tii should have twice the resistance as that in a non-tii, so the tii resistance wire is twice as long, and it makes sense that it runs all the way to the fuse box.

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Help!!!

So I spliced a new wire in to the green wire where the resistance wire was previously spliced. I connected that to the resistor and then the resistor to the + end of the coil.

I ran the red/black wire directly to the coil.

When I went to start the motor....no luck. It turned over but wouldn't start.

So I disconnected the wire from the resistor and ran it directly to the coil. It fired right up.

Any thoughts?

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Does the engine fire during cranking (i.e. when the key is in the Start position)?

Disconnect the wire from one end of the resistor, and measure the resistor with an ohmmeter. Is it 1.8 ohms?

Please confirm:

- Green wire from fuse to one end of the resistor

- Wire from other end of resistor to coil +

- Red/black wire to coil +

- Original resistance wire is disconnected at one or both ends

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