I recently posted saying a local shop had shorted wires in both of my front wiring harnesses on my 68 and melted both harnesses. I changed both harnesses and was very careful to switch one wire at a time to make sure everything was done right and now the engine won't start. It is only getting 4 1/2 volts to the + terminal on the coil with the key on. I am concerned that it might have damaged the MSD ignition also. Could that have fed current back to the ignition and cause damage ? When I bought the wiring harnesses from Brian at Bair's corvettes he said that wouldn't effect the MSD circuit but I don't seem to have enough juice at the coil with only 4 1/2 volts. How can I test the whole MSD system to see if it is working properly.

 

Log on MSD's website...they have a forum and troubleshooting areas you can surf and ask questions.

 

You should have the full 12V at the coil when cranking the engine if you're running the stock points type ignition. If not then the yellow bypass circuit from the starter is not connected properly.

 

He is correct, there should be a yellow cloth sleeved wire from the solinoid to the + lead of the coil. It will supply +12v to the coil during cranking, as stated. Better check the wiring to the MSD, and check to make sure that it's correct, and that a resistance wire is used with it. If not, you'll have to run a bypass. The resistance wire should read about 1.35 Ohms and is from the bulkhead connector in the engine compartment to + lead of the coil. The second bypass wire is from the soliniod to the + lead of the coil. this is from a '73,, yours should be simliar. Incedently, if you remove the resistance wire from the coil it should read +12V, free. Also check your engine to frame ground cable, and batt to frame ground cable, and main Batt + cable.
Incedently, the two main front hanresses may have smoked, but they have to get their current from somewhere. besides the main batt hook up at the horn relay, they also get it from is the main interoir harness. If your fronts fried, then I would take a really good look at the interior main harness wiring, for melted insulation.

 

The car has MSD electronic ignition and I only have 4 1/2 volts at the + terminal on the coil. Need to know how to test the MSD system to see if it is functioning.

 

100%

 

This was taken directly from the MSD web site, the comment about the yellow wire is wrong.

TROUBLESHOOTING
Every MSD Ignition undergoes numerous quality control checks including a four hour burn-in test. If you experience a problem with your MSD, our research has shown that the majority of problems are due to improper installation or poor connections.
The Troubleshooting section has several checks and tests you can perform to ensure proper installation and operation of the MSD. If you have any questions concerning your MSD, call our Customer Support Department at (915) 855-7123, 8 - 5 mountain time.
LED
The LED on the side of the MSD monitors several operating conditions of the MSD. If the LED indicates that there is a problem with the ignition system, follow the steps through the Troubleshooting section. The LED will appear to be on steady at above idle speeds when everything is functioning properly.
• Flashes once per second if the battery supply voltage is low when under 3,300 rpm (while
multiple sparking). This indicates a charging problem or poor connection.
• It will flash approximately once per second if the battery input voltage is above 27 volts for
a sustained amount of time.
• The LED will flash for every trigger signal from the distributor or crank trigger. You can take
advantage of this when statically setting the timing when using the White wire to trigger.

http://www.msdignition.com/downld1.htm