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Old 09-16-2019, 06:21 PM
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Transitorized Ignition Module

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Old 09-17-2019, 08:23 PM
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I'd be looking at the green , green / yellow wire running into the distributor. I " think " this system uses am old style contact point arrangement to trigger the ignition module.

Make sure the brown wire at the module is grounded.
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Old 09-17-2019, 09:28 PM
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There is a thread in the veteran's section about replacing the transistor in the ignition module. It's pretty straight forward with a soldering iron and the part is a few bucks, plus shipping.

The quick test of it is the little green wire at the top of the diagram, hook up a dwell meter to that. Zero dwell while cranking means you have short or a dead box.

BTW, that box must be grounded well; usually the three bolts to the firewall provide that ground. If you snag a replacement box, make sure to actually mount it correctly before firing it up.

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Old 10-04-2019, 09:11 AM
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Is there a resistance check that can be done on the distributor itself? I have a 78 450sl with a no spark condition aswell! I've done quite a bit of reading and thru some tests I feel I've determined the distributor has failed. But I want to confirm it, just cant find a "test" for it. (I dont have a way to monitor dwell). I have battery voltage to ignition coil with key on, 9v while cranking (which means the ignition switch, ballast resistors and everything up to the ignition coil is good) resistance checks on the coil itself check out (.4 ohm and 10.5 kohm, within spec on both), green wire to dist. is brand new, aswell as cap/rotor/plugs/wires, tested terminals 4 and 5 for voltage at diag port (0v like there should be, meaning switchgear/ignition box is good). Which leaves the distributor..... thoughts?

I can provide more detail on what tests were run to determine all of my findings, but its everything that can be found thru google/prodemand(mitchell)

Any and all help is much appreciated!!
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Old 10-04-2019, 09:46 AM
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Originally Posted by allimport View Post
Is there a resistance check that can be done on the distributor itself?

Pull the green wire plug from the ignition box, check for resistance between center pin and the shield. 600+/-100 ohms.
Under what conditions was the green wire renewed? What was the cause? By whom performed?
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Old 10-30-2019, 04:24 PM
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Originally Posted by 1974450sl View Post
I am still unable to start the engine after all the above diagnostic procedures. Anyone able to offer any insight please?
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Old 10-31-2019, 07:04 AM
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9V while cranking is too low. Hav you tried with jumper cables form a running car?

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