Ignition coil resistor in wiring?

[HBChris]

There was a resistor in my 75.

['76mintgrün'02]

15 minutes ago, HBChris said:

There was a resistor in my 75.

 

I nabbed the photo from your link above

 

 

 

 

 

I just reread the article in the reference section, "Ignition Coil Myths Busted"

 

https://www.bmw2002faq.com/articles.html/technical-articles/electrical-and-ignition/ignition-coil-myths-busted-r52/

 

and found this info about the resistor wire--

 

Also on '74 and later, the obvious ceramic resistor was replaced by a sneaky, "special" resistance wire that runs in the harness from somewhere over the engine to the coil's positive terminal - it has clear insulation and a molded marker at the coil end with the resistance value on it (by now those are usually just a blob of crispy rubber). All resistors for all years were 1.8 ohms, according to the factory manual.

 

I suspect that little piece is a label, not a resistor. Either way, why would it be .9, as opposed to 1.8 Ohms?

It would be interesting to see what an Ohm meter says, if you place the leads on either side of that little block.

 

(My '76 does not have that little white piece on the resistor wire).

[JohnS]

1 hour ago, '76mintgrün'02 said:

 

I suspect that little piece is a label, not a resistor. Either way, why would it be .9, as opposed to 1.8 Ohms?

It would be interesting to see what an Ohm meter says, if you place the leads on either side of that little block.

 

(My '76 does not have that little white piece on the resistor wire).

 

The square taillight 2002tiis have a resistor wire that's twice as long as the ones used on "regular" square taillight 2002s and has 1.8 ohms of resistance.  The longer the resister wire, the more resistance... The original black coils used on "regular" 2002s specify to use a resistor with 0.9 ohms resistance.  Not to be confused with the original black coils used on 2002tiis that specified to use a 1.8 ohm resistor.  Hope that makes sense...

Edited March 13, 2020 by JohnS

[JohnS]

Just an FYI, the '74 3.0 csi that I used to own had a little plastic yellow tag on the resistor wire that was labelled 0.9 ohm.

[HBChris]

7 hours ago, '76mintgrün'02 said:

 

I nabbed the photo from your link above

 

 

 

 

 

I just reread the article in the reference section, "Ignition Coil Myths Busted"

 

https://www.bmw2002faq.com/articles.html/technical-articles/electrical-and-ignition/ignition-coil-myths-busted-r52/

 

and found this info about the resistor wire--

 

Also on '74 and later, the obvious ceramic resistor was replaced by a sneaky, "special" resistance wire that runs in the harness from somewhere over the engine to the coil's positive terminal - it has clear insulation and a molded marker at the coil end with the resistance value on it (by now those are usually just a blob of crispy rubber). All resistors for all years were 1.8 ohms, according to the factory manual.

 

I suspect that little piece is a label, not a resistor. Either way, why would it be .9, as opposed to 1.8 Ohms?

It would be interesting to see what an Ohm meter says, if you place the leads on either side of that little block.

 

(My '76 does not have that little white piece on the resistor wire).

 

Maybe you’re correct.  I removed it and tossed it, it also had the clear wire as I recall.

 

 

[Chris_B]

Keeping in mind that the resistor wire only works with a relay driven by the starter circuit 

 

 

['76mintgrün'02]

On 3/13/2020 at 11:49 AM, JohnS said:

The square taillight 2002tiis have a resistor wire that's twice as long as the ones used on "regular" square taillight 2002s and has 1.8 ohms of resistance.  The longer the resister wire, the more resistance... The original black coils used on "regular" 2002s specify to use a resistor with 0.9 ohms resistance.  Not to be confused with the original black coils used on 2002tiis that specified to use a 1.8 ohm resistor.  Hope that makes sense...

 

Yes, that makes sense.  Thank you for the clarification.  That information would be nice to add to the comment section at the bottom of the "Coil Myths" article; (where it states that all resistors were 1.8 Ohms).

 

43 minutes ago, Chris_B said:

the resistor wire only works with a relay driven by the starter circuit 

 

I think there was a relay involved with the ceramic resistors on earlier cars, but am not aware of one on my '76.

Where is it located?

[Chris_B]

it typically was mounted on the firewall directly behind the dizzy

['76mintgrün'02]

Jimk explains the relay / resistor / starter systems in this post.

 

 

[John76]

On 3/14/2020 at 10:08 PM, '76mintgrün'02 said:

think there was a relay involved with the ceramic resistors on earlier cars, but am not aware of one on my '76.

Where is it located?

 

My '76 does not have a dedicated relay...doesn't need one cuz it has the starter wire (black/red) for starting, and the resistor wire for cruising.  The 1.8 Ohm spec mentioned does make sense. A .9 Ohm coil with a .9 Ohm resistor (ceramic or clear wire) equals 1.8 Ohms.

The length of the resistor wire square-tail non-Tii cars gives .9 Ohm resistance. Double the length for the '74 Tii will give 1.8 Ohms.

Does anyone know the coil model numbers (w/resistance values) for the square-tail Tii and the non-Tii models??

[thinksound_mike]

I have a blue coil and that IE dizzy. It's been several years, but I don't recall doing anything with a resistor when I installed it. I just dropped it in when the engine was at TDC and then did the timing after. 

[Santawillis]

This post actually explains the coil situation the best so I am bringing it back from dead.

 

My original California 76' has the .9Ohm resistor and I replaced the original dead coil (not sure why it was dead) with an autoparts store 1.5 Ohm coil, its been running well enough. My question is, is running a 1.5 ohm coil when the original black coil is .9ohm really make a considerable difference? Car is idling fine? Am I running a total resistance of 3.3ohms? .9 from resistor, ,9 from cable and 1.5 from coil? 

 

What am I missing here? This whole coil discussion seems endless! HELP! @John76 is my usual savior!

[John76]

Here's how the original late-model ignition system worked.

Ignore/erase the RED wire which is only used for a direct bypass of the resistor wire with a low-resistor coil and a PerTronix II ignition.

I'll make a sketch of the external resistor with relay system ... shortly.

John

 

[JohnS]

The new black 😄

 

[Dudeland]

On 3/28/2023 at 5:06 PM, Santawillis said:

This post actually explains the coil situation the best so I am bringing it back from dead.

 

My original California 76' has the .9Ohm resistor and I replaced the original dead coil (not sure why it was dead) with an autoparts store 1.5 Ohm coil, its been running well enough. My question is, is running a 1.5 ohm coil when the original black coil is .9ohm really make a considerable difference? Car is idling fine? Am I running a total resistance of 3.3ohms? .9 from resistor, ,9 from cable and 1.5 from coil? 

 

What am I missing here? This whole coil discussion seems endless! HELP! @John76 is my usual savior!

Don't forget that the rotor has a resistor.  See my avatar...  MSD+0 Ohm wires = melty melty.