Amazon: Electronic Ignition

[142 Guy]

Originally Posted by dcthompson

1. I have seen various recommendations for a coil, with the Bosch Blue the most popular. I have seen nothing on using the original coil. I have never had a problem with the original coil. Is there anything wrong with keeping it in service?

The critical limit that you have to respect is the minimum resistance of the coil. The resistance of the coil establishes the peak current that can flow through the coil and the Pertronix / 123 / (whatever brand) electronics. Find out what 123's recommendations are for the minimum coil resistance. Measure or look up the resistance for your original coil and if it is higher than 123's recommendations then you are good to go with your original coil.

If you determine your coil resistance by measurement with a multi meter, be aware that measuring low resistance values is tricky. If your multi meter has a zeroing function, use it to zero the resistance with the test leads shorted out before measuring the coil resistance. If you don't have a zeroing function (most do not), short the test leads together, measure the resistance of the test leads and write this down. Then measure the resistance of the ignition coil and subtract the resistance of the test leads from this value to get a more accurate coil measurement. Also, clean the spade contacts on the coil to reduce the contact resistance when you are doing the measurement. When you are measuring something that has a resistance of 10,000 ohms, the test lead resistance and contact resistance introduces minimal error. When you measure something with 2-3 ohms resistance, the test leads and contact resistance can introduce very significant errors. You don't want to measure 3.0 ohms and then find that you cooked your 123 because you actually have a 2.0 ohm coil. Also, be aware that aside from test lead resistance and contact resistance problems, the bargain basement multi meters generally don't measure low resistance values accurately. If you don't have a good meter like a Fluke or similar, you might want to see if you can borrow one.

For what it is worth, I ran the stock Bosch coil in my 1971 142 E with a Pertronix module without issue; but, the Pertronix module may have a different current limit than the 123. Find out what 123's recommendations are for minimum coil resistance and then check your coil to see if it respects that limit

[Bracpan]

As I said 123 recommend the Blue Bosch coil that has 3 Ohms resistance.. Its on the 123 website.. and if easier its for sale as a package, dizzy, Blue coil, plugs and leads if needed.... !
123 will work with a coil of less ohms but why take the risk ?