engine and drivetrain No brainer wiring question - Ballast resistor

[grotflo]

I am replacing my worn out dizzy with a new one from Ireland Engineering. My car is a 1975 so it should have the built in 0.9 ohm resistor wire, but it seems the PO removed it. I'm installing both the new distributor and a new red coil, and which means I'll also have to install a ballast resistor. Is the attached image the correct way to wire all these up? I've read through a bunch of posts about ballast resistors but nothing talks about how to add one, just remove them. Thanks all!

[Stevenc22]

This diagram seems wrong.

If I recall.

Positive wire off #12 fuse through ballast resistor to coil. Negative wire off coil to ignition. Then just put the petronix off the positive and negative on the coil.

[HBChris]

The original black coil used a 0.8 ohm resistor, the replacement red coil needs a 1.8 ohm resistor, it is stated on the label. IE should know this. It's available at AutohausAZ, look up by Bosch part number 0 227 901 014. My NK sedan uses a relay to bypass the resistor at startup so wires are green, yours likely has no relay, so I can't help with wiring.

Edited April 21, 2015 by HBChris

[Buckeye]

PM sent.

[thehackmechanic]

The purpose of the ballast resistor is to be bypassed during starting, and to come into play the rest of the time. Your wiring diagram shows the ballast resistor always in play. It needs to be bypassed during starting. 

 

Wiring up the ballast resistor can be done in two ways, and it has nothing to do with the Pertronix, so let's deal with it first and then come back to the Pertronix.

 

If your starter has a separate terminal on it that supplies 12V when the key is turned (I forget which years they had this), then you connect that terminal directly to coil terminal 15 (the + terminal). You also connect the ignition switch to the input of the ballast resistor, and the output of the ballast resistor to coil terminal 15. In that way, when the key is turned to start, the ballast resistor is bypassed (which is the half the purpose of the ballast resistor -- to be bypassed while starting) and the coil is fed 12V. And when the key is backed off from start to ignition, the ballast resistor is powered, which cuts the voltage to the coil (which is the second purpose of the ballast resistor, -- to be in play at all times other than starting).

 

Well, just to be clear, the ballast resistor is ALWAYS powered. Terminal 15 should have two connections to it -- one directly from the starter, and the other from the ballast resistor. If it's getting 12V from the starter, it uses it. If not, it uses the reduced voltage from the ballast resistor.

 

At some point, 2002s stopped having the starter with the extra terminal on it, and they began using a relay to switch the ballast resistor instead. The wiring of the relay is described in a number of posts. Here are two. I haven't checked them for accuracy.

 

http://www.bmw2002faq.com/topic/112053-q-rewiring-to-elminate-ballast-resistor-new-bosch-blue/

 

http://www.bmw2002faq.com/topic/82140-relay/

 

With any relay, terminals 86 and 85 are the low current connection to turn on the electromagnet in the relay, allowing high current to flow from terminal 30 to terminal 87. So you can see that, with both of these descriptions, what's happening is that, when you turn the key to start, it's supplying voltage to 86, which connects through 85 to ground, which energizes the electromagnet, which sends voltage from terminal 30 to 87, which goes directly to coil terminal 15, supplying the coil with full voltage. As is the case without the relay, the input of the ballast resistor is also connected to the ignition, and the output is connected to terminal 15, so when the starter isn't being cranked, a reduced voltage is supplied to 15. As was the case with the starter connection, terminal 15 should have two inputs -- one from the relay, the other from the output of the ballast resistor.

 

Now, the Pertronix wiring. It's shown here:

 

http://www.pertronix.com/support/manuals/pdf/ignitor12vneg.pdf

 

When a ballast resistor is used, it shows the red wire connected to the input side of the ballast resistor, and the black wire to terminal 1 (the - terminal) of the coil. So that part of your diagram looks right.

 

But check and double-check. I've blown up two of these, one from not having a matched coil and ballast resistor (the total series resistance from the input of the ballast resistor to coil terminal 1 MUST NOT BE LESS THAN 3 OHMS OR IT IS LIKELY TO COOK THE PERTRONIX), and second one from just being a dope.

 

--Rob

The purpose of the ballast resistor is to be bypassed during starting, and to come into play the rest of the time. Your wiring diagram shows the ballast resistor always in play. It needs to be bypassed during starting. 

 

Wiring up the ballast resistor can be done in two ways, and it has nothing to do with the Pertronix, so let's deal with it first and then come back to the Pertronix.

 

If your starter has a separate terminal on it that supplies 12V when the key is turned (I forget which years they had this), then you connect that terminal directly to coil terminal 15 (the + terminal). You also connect the ignition switch to the input of the ballast resistor, and the output of the ballast resistor to coil terminal 15. In that way, when the key is turned to start, the ballast resistor is bypassed (which is the half the purpose of the ballast resistor -- to be bypassed while starting) and the coil is fed 12V. And when the key is backed off from start to ignition, the ballast resistor is powered, which cuts the voltage to the coil (which is the second purpose of the ballast resistor, -- to be in play at all times other than starting).

 

At some point, 2002s stopped having the starter with the extra terminal on it, and they began using a relay to switch the ballast resistor instead. The wiring of the relay is described in a number of posts. Here are two. I haven't checked them for accuracy.

 

http://www.bmw2002faq.com/topic/112053-q-rewiring-to-elminate-ballast-resistor-new-bosch-blue/

 

http://www.bmw2002faq.com/topic/82140-relay/

 

With any relay, terminals 87 and 86 are the low current connection to turn on the electromagnet in the relay, allowing high current to flow from terminal 30 to terminal 85. So you can see that, with both of these descriptions, what's happening is that, when you turn the key to start, it's supplying voltage to 86, which connects through 85 to ground, which energizes the electromagnet, which sends voltage from terminal 30 to 85, which goes directly to coil terminal 15, supplying the coil with full voltage. As is the case without the relay, the input of the ballast resistor is also connected to the ignition, and the output is connected to terminal 15, so when the starter isn't being cranked, a reduced voltage is supplied to 15.

 

Now, the Pertronix wiring. It's shown here:

 

http://www.pertronix.com/support/manuals/pdf/ignitor12vneg.pdf

 

When a ballast resistor is used, it shows the red wire connected to the input side of the ballast resistor, and the black wire to terminal 1 (the - terminal) of the coil. So that part of your diagram looks right.

 

But check and double-check. I've blown up two of these, one from not having a matched coil and ballast resistor (the total series resistance from the input of the ballast resistor to coil terminal 1 MUST NOT EXCEED 3 OHMS OR IT IS LIKELY TO COOK THE PERTRONIX), and second one from just being a dope.

 

--Rob

Edited January 3, 2020 by thehackmechanic

[grotflo]

Thanks for the detailed responses, I appreciate all the good advice. This is why I love these forums. I need to check under the hood tomorrow and see if I have a wire from the starter to the coil. I don't recall seeing a relay anywhere in my car, but I could be wrong.

One more quick question about the IE distributor - it claims to be "Pertronix-like" on their website. Does that mean it is wired the same?

[thehackmechanic]

I don't know for certain, but I would suspect so. 

[wegweiser]

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?

Edited April 21, 2015 by wegweiser

[thehackmechanic]

Paul is, of course, correct, and I am a doofus typing too quickly. I have corrected it in the text above so as not to lay electric land mines for other searchers to step on.

 

http://www.12voltplanet.co.uk/relay-guide.html

[wegweiser]

Rob - you've been doing this longer than me....so I thought maybe I was missing something, or simply misinterpreting your phrasing! Whew! This means I won't arrive at the shop to see 3 cars engulfed in flames, today!

[Conserv]

n/t

Edited April 21, 2015 by Conserv

[Conserv]

GREAT explanations/summaries/clarifications from Rob and Paul! Wish I'd known half of that 20 years ago, or even a quarter of it 40 years ago!

Thanks and regards,

Steve

[grotflo]

I took some photos of my current setup.  I can't seem to find any relay that you guys are talking about.  Does everything look right here?  My car was a 2002 automatic that was converted to a 4-speed at some point, so maybe the wiring is different for that reason? Thanks for the knowledgable replies - I'm trying to learn as I go here.

 

 

[grotflo]

Based off Steve's post, should it look like this?  It doesn't show the wire from the starter to terminal 15 on the coil.  Rob, if you look at the first photo of the starter I posted, where on the starter would it attach?  Do you see it there?

 

 

 

 

[HBChris]

Only early cars have relays, I think Rob has it backwards. Both my 69 NK and former 02 have them.