The Bosch blue coil in my '74 is bad, looking for a replacement (compatible with the Crane XR 700 electronics I would like to keep for the time being.) In a search I read that a Bosch red coil is the way to go. Is this what Rock Auto is selling?
Bosch red coil?
- Thread starter bill
- Start date
Your 74 has an inline resistor wire instead of a ballast resistor so the blue coil is not ideal. I don’t know if the Crane makes this a moot point or not however. I would use the red coil.
Amazon sells the Bosch red coil. Do you still have points? If so keep the resistor wire. If not bypass it.
"The XR700 unit is designed for ballasted ignition system, a needing 1.6-ohm coil and 1.6-ohm ballast resistor. The electronic unit normally runs on 6-7 volts and tolerates a momentary 12 volt input during crank starting (same as the ballasted ignition coil)."
I believe the red coil has 1.8 ohms of resistance and the blue coil 3.4 or so. The red is designed to run with a ballast resistor (or resistor wire) and the blue without.
With both the blue coil AND the resistance wire I don't think the car would run great...especially at high RPMs.
I would do some more digging, however. Measure the resistance on the hot wire (resistance wire) going to the + side of the coil. Call the Crane tech line and let them know what you have and what you want to do and get their recomendation.
I believe the red coil has 1.8 ohms of resistance and the blue coil 3.4 or so. The red is designed to run with a ballast resistor (or resistor wire) and the blue without.
With both the blue coil AND the resistance wire I don't think the car would run great...especially at high RPMs.
I would do some more digging, however. Measure the resistance on the hot wire (resistance wire) going to the + side of the coil. Call the Crane tech line and let them know what you have and what you want to do and get their recomendation.
Dick, you hit the nail on the head, great research.
That settles that!
Thanks everyone. Looks like the blue coil with the resistance wire was a mistake.... it worked, though, for 10 years (I don't rev above 3000 out of respect for the old girl, so I didn't notice any high performance problems.) I'll call whoever bought Crane and double check if the red coil/resistance wire combination is OK. Great forum!
Jeff Hecox
New Member
Here is a good breakdown of the different Bosch ignition coils on the BMW2002faq page. https://www.bmw2002faq.com/articles...-and-ignition/ignition-coil-myths-busted-r52/
Can Dick get awarded a Star or something? Perhaps a "Thumbs Up"? That was really good!
Even the blind squirrel finds a nut once in a while.Can Dick get awarded a Star or something? Perhaps a "Thumbs Up"? That was really good!
That 2002 FAQ article confirms what Dick said and what I can now do in peace: run a red coil with the resistance wire as ballast. Thanks very much!