engine and drivetrain No brainer wiring question - Ballast resistor

[grotflo]

Thanks HBChris, I wasn't sure about that.  So does anyone want to chime in on the wiring diagram?  Does it look correct?  And where on the starter should I look for the wire that runs to the coil?

[FunkyLaneO]

Rob! Don't you mean terminal ***87*** gets voltage from the battery (terminal 30) when the relay is energized????? 

 

I use the following to set up common 4 pin Bosch and many other relays:

 

30 - battery power

85 / 86 - switched power or ground to energize the relay (often - but not always -  interchangeable.)

87 - voltage out to the consumer (fan, light, horn, etc)

 

If I'm wrong - SCHOOL me.... but this is how I've always installed / troubleshot relays. Am I missing something, or is your previous info just a typo?

 

This is correct but... if you are using an SPDT relay, in practice it is preferred to run the battery to 87 and have 30 power whatever is being supplied power.  The reason is it you put constant power to terminal 30 then terminal 87a (normally closed) will always be energized and if it is not being used it will be exposed and vulnerable to shorts. If both 87 and 87a are used in a scenario then it doesn't really matter or if you are using a relay that doesn't have an 87a terminal (SPST) it doesn't matter either.

 

 

As for the most recent diagram, eliminate that wire from your ignition to the coil, that wire should go to your tach, terminal 12 on your fusebox is controlled by the ignition switch.

 

Since yours is a 75 then it should have a resistor wire and not a fender mounted ballast resistor, do not use both together.  Make sure you have your bypass wire on the correct terminal on your starter because if you don't it will attempt to backfeed your starter and your resistor will burn up and the wire will get fried.

Edited April 21, 2015 by FunkyLaneO

[HBChris]

Using a voltmeter you can test the small starter terminals to see which one is hot only with starter engaged.

[Stevenc22]

Funkylane is correct. The #12 fuse is driven by ignition. The ground wire heads to the tach and should already be the black wire in the wiring loom attached to the coil.

 

This method of wiring does not bypass the ballast resistor during startup which is what Rob was trying to discuss. However later cars never had a bypass so this should work just fine.

Edited April 21, 2015 by Stevenc22

[thehackmechanic]

It looks to me, from the picture of your starter, that you DO have the extra terminal on the starter. Looking closely at the pic, I see it above the terminal from the ignition that has the wire on it. As HBChris said, do you have a voltmeter? If you do, set it to measure voltage, and carefully hold it onto that terminal making sure it's not touching anything else. Put the negative wire of the voltmeter to ground. You should have no voltage on it. Have a friend turn the key to ignition. You should still have no voltage on it. Have a friend try and start the car. You should now see voltage on it (probably less than 12v because the starter is pulling it down). If you DO see voltage on this other terminal when the starter is cranked, then make a wire to connect this terminal to.... oh let me just list them all separately.

 

Extra starter terminal --> Coil terminal 15 (the one with the +) [but only if there is 12V on the extra starter terminal when the starter is cranked.]

Whatever is currently feeding coil terminal 15 (probably fuse 12) --> Ballast resistor input

Ballast resistor output --> Coil terminal 15

Pertronix --> Connect as per Pertronix documentation (red wire to input of ballast resistor, black wire to coil terminal 1 (the one with the -)

 

--Rob

[grotflo]

Thanks so much everyone!  It's amazing how much shared knowledge you guys have.  I'll check out that voltage on the starter and see what's going on there.  Thanks for the clear instructions on how to measure that voltage.

 

Ireland Engineering says that, "The igniter requires at least 2 ohms of resistance in the coil OR an external ballast resistor to limit the current flow.  If you use the factory BMW coil or a Bosch Red coil (which is what I'm using), you must use the external resistor."  So even if my car has the resistor wire (which I'm not sure it does), I still need a resistor right?  The resistor wire would go to the 15 terminal on the coil, correct?  I traced that red wire all the way to the fuse box and I don't see any clear/yellowing wire that indicates the resistor wire.  I guess I'll have to measure the resistance on that red wire, but it seems that I still need a ballast resistor.  

 

[1972-2002]

I am using a blue bosch and when I last checked in the forum said I didn't need the ballast resistor for my 72 is that still correct?

 

Garry

[HBChris]

The Blue coil has an internal resistor, do not use an external resistor with this coil.

 

grotflo, yes, you need the 1.8 ohm external resistor, see the part number I provided earlier.  My 1969 02 would stall for no apparent reason on the freeway and then restart after 30 seconds, it had the red coil and original 0.9 ohm resistor.  When I switched to the correct resistor the problem went away.

[Stevenc22]

Grotflo, your diagram is getting alot closer to being right but i think there is a problem with the petronix wiring. The petronix should be after the ballast resistor. The petronix wants 3 ohms of resistance. Since you have it joining the same side of the ballast resistor as the #12 fuse, it is going to get pre-ballast voltage and will burn out. Just plug the + of the petronix directly to the coil so that it gets post ballast voltage.

[grotflo]

Thanks Steven, I didn't notice that before.  So like this then?  That means three wires connect to the + terminal on the coil.

 

[FunkyLaneO]

That will work, but make sure that you plug the wire to the starter on the correct terminal of the starter, I cannot stress that enough, you do not want to start a fire. Unless you live someplace that gets really cold then you really don't need the bypass wire, I got rid of mine a long time ago but it never gets cold in San Diego so my car starts fine every time.

[grotflo]

Well I am in sunny Atlanta, so seeing as it doesn't get cold here very often, I may initially try it without the bypass wire from the starter. If I find it's not cranking come wintertime, I can dig up this thread and go through the steps to add it. Thanks again to all who shared their wisdom here. Hopefully my crude diagram will help someone else in the future.

[Stevenc22]

^Bingo!

[thehackmechanic]

<<The petronix should be after the ballast resistor. The petronix wants 3 ohms of resistance. Since you have it joining the same side of the ballast resistor as the #12 fuse, it is going to get pre-ballast voltage and will burn out. Just plug the + of the petronix directly to the coil so that it gets post ballast voltage..>

 

I am not sure that the above is correct.

 

Attached is the wiring diagram from Pertronix itself. The illustration furthest to the right (the one with both the ballast resistor and the Pertronix) seems to clearly show, when a ballast resistor is used, that the red Pertronix wire should be connected to the input side (the 12V side, the side the ignition wire is connected to) of the ballast resistor. Yes, the Pertronix wants to see a coil-ballast resistor combination with no more than 3 ohms of total resistance, and yes I've blown up Pertronix units before by running them with a coil-resistor combination that had too little resistance, but this is because too little resistance creates too much current. The whole purpose of the ballast resistor is to act as a current-limiting resistor that is bypassed during starting and enabled at all other times. The way it is shown wired in the attached picture, I believe that it limits current through the Pertronix, which is what you want. Wiring the red Pertronix wire directly to the coil, I believe, does not limit current.

Edited April 23, 2015 by thehackmechanic

[grotflo]

Hmm. I was reading over the instructions for the IE distributor (http://www.bmw2002.com/gallery/v/tech/IEdistributor/) and it doesn't mention anything beyond connecting both wires to the coil. Maybe someone with IE could weigh in...