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1970 Mark III, No Spark

Hello Bill,

I have a 70 Mark 3 and have had some starting issues lately. Went through two rebuilt carbs and finally ended up with a new Edelbrock. Installed the new carb and no start. Did many of the usual checks and determined the carb was good to go, but no spark. Ran a jumper wire directly from the battery to the positive side of the new coil and boom, she fired right up. So, that being the case, do I likely have a bad voltage regulator? Alternator? Or ignition switch? Seems the coil is getting no or weak power from its source. If I remove a plug and crank the motor I do get spark, but it seems weak.


Thanks in advance!

Steve

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Hello Steve -

From your description, it does seem that you have no power to the coil from the start/run circuit. When the key is rotated to the Start position power is sent from the ignition switch to the starter solenoid that is mounted on the starter. The solenoid engages the starter and at the same time sends full 12v to the coil for easier starting while cranking. After the engine starts and the key is released to the Run position, power is then sent from the ign. sw. to the coil via a resistor wire which is installed (buried) in the wiring harness under the dash assy. The resistor wire drops the coil voltage to a lesser voltage so that the points do not burn out. Power to the ignition sw. is through a wire that is attached with the battery positive cable that attaches to a connection at the starter. A fuse link is also built into this wire behind the engine from the starter to the ign. sw. You may have an electrical disconnect or burnout somewhere in the circuit or a bad ign. sw. etc. Good places to look for wiring problems are in the harness at the back of the engine to the starter and coil. In any case the power path for this circuit will need to be carefully tested for continuity in order to pinpoint the problem. To do that properly a correct wiring diagram will be very necessary for you or your technician to follow. We stock many parts that you may need for this and other repairs. Let us know what you find.

Sincerely,

Bill