Author Topic: 123 ignition change on 1971 280 SL with transitorized ignition  (Read 2411 times)

Woodstock

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I am in the process of switching out my stock distributor with a 123 ignition Bluetooth distributor.  My mechanic has concerns about the need to bypass the transistorized ignition system when installing the new 123 Ignition.  The instructions are not specific about this model.  Will this conversion require a different coil?  We have concerns that we could fry the 123 if we don't do this properly.  Any help with this matter would be appreciated.

Randy K

mbzse

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Re: 123 ignition change on 1971 280 SL with transitorized ignition
« Reply #1 on: November 18, 2018, 17:51:54 »
Quote from: Woodstock
.../...a 123 ignition.../...to bypass the transistorized ignition system when installing the new 123 Ignition.../...
Remove all traces of the present old (transistorized) Ignition system. Yes, useful step to exchange the ignition coil also, for a new one (these devices degrade with time, remember some 50yrs have passed...)

I paint my ignition coils black, see image below. Blue coil in other picture is "as bought"
« Last Edit: January 06, 2020, 12:42:44 by mbzse »
/Hans S

Tyler S

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Re: 123 ignition change on 1971 280 SL with transitorized ignition
« Reply #2 on: November 18, 2018, 17:52:28 »
The transistorized ignition will need to be disconnected as the 123 has its own transistorized control built in. The coil must have resistance of at least 1.0 ohms. The Bosch “Red” coil (0 221 119 030) is a good replacement. Be sure to bypass the ballast resistors. You can leave them in place for visual asthetics. Just move the wire going to the coil over to the input side of the balast resistor. If you have the secondary ballast resistor for increased cranking voltage, it can be disconnected.
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Woodstock

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Re: 123 ignition change on 1971 280 SL with transitorized ignition
« Reply #3 on: November 18, 2018, 20:57:14 »
Thanks for the information .... this confirms our concerns regarding just hooking the distributor up via the instructions were legitimate.

Randy