White Wire from MSD 6A... 12v?

rockreid · 10-17-2014, 07:04 AM

Is the white wire from a MSD 6A box supposed to provide a constant voltage? Reason being I am trying to diagnose a no spark situation in my 73.5 Targa 2.4 restoration.

I never even tried the original CIS ignition system (which I still have) and before I re-gap all the spark plugs and hook up the wiring for that system I want to verify whether my MSD box or Blaster coil is fried or not.

I've tried my multimeter on the MSD white wire with Key On and get no primary voltage. I get no spark cranking the engine.

My stock engine rebuild started strongly and ran for about 5 minutes 2 weeks ago then died in my driveway . My fuel distributor is away being rebuilt right now but in the meantime I need to get my ignition system up and running. I am running out of ideas on how to test the MSD box and coil.

whiskyb · 10-17-2014, 07:08 AM

My drawing shows the white wire as being un-required in our installs

rockreid · 10-17-2014, 07:59 AM

doesn't the White wire go to the points?

dicklague · dicklague's Garage

White wire is the points trigger. don't put 12 vdc to this wire!!

here is a basic diagram:

rockreid · 10-17-2014, 08:58 AM

no, I didn't put 12v to it lol.

But I do think my burning out the MSD box is a possibility because my new Bosch alternator was putting out 17.75v while the engine was running. I checked running voltage across the battery terminals before the engine sputtered out. I already have a new voltage regulator installed but am waiting for my rebuilt fuel distributor to show up.

As for the MSD, I wish I had a known good unit lying around, but it seems like it's off the an auction website for me to pick up a used one. I have a Blaster 2 coil and was wondering if the stock CIS unit can work with that (as well as my upgraded spark plug wires for the MSD system). In the meantime I am also re-gapping my plugs down to 0.040 from the initially recommended MSD 0.050 to see if that helps.

Walter_Middie · Walter_Middie's Garage

Rockreid,

Do a search on "telegraph test".

To troubeshoot you need to check if the points close, and if the wire from the points to the CDI box shows continuity to GND when the points are closed.

Next connect a spare spark plug with a high-tension wire straight to the coil. This removes the rotor and cap from the equation. Once the points close it should produce a spark. You can jam a small screwdriver into the points contacts to ground them. Then turn the engine over and see if it works that way too.

Once you are to the point where a turning distributor produces sparks with a single spark plug connected to the coil, you can add the distributor to the equation.

dicklague · dicklague's Garage

Quote:

Originally Posted by Walter_Middie

Rockreid,

Do a search on "telegraph test".

To troubeshoot you need to check if the points close, and if the wire from the points to the CDI box shows continuity to GND when the points are closed.

Next connect a spare spark plug with a high-tension wire straight to the coil. This removes the rotor and cap from the equation. Once the points close it should produce a spark. You can jam a small screwdriver into the points contacts to ground them. Then turn the engine over and see if it works that way too.

Once you are to the point where a turning distributor produces sparks with a single spark plug connected to the coil, you can add the distributor to the equation.

rockreid PM me. I have a square wave generator that simulates the distributor out put and a tester plug that I can loan you to bench test the MSD. the tester works like this:
https://www.youtube.com/watch?v=8Qb9JxX-mLg

I would be happy to loan this to you for a few days to bench test the MSD. I will send my tester [not the MSD in the video but simpler] and an adjustable spark plug tester.

This way you don't have to borrow an MSD to test.

PM me.

rockreid · 10-17-2014, 05:51 PM

well, no matter what I do I get no spark. I performed the "telegraph test" and nothing. I have a Led light spark plug tester and nothing from that either. I called and got an RMA from MSD so we'll see what their repair tests indicate.

In the meantime, I am picking up an auction unit as a backup and will use that to get the car running, at least when my fuel distributor is done and shipped back to me. It will never hurt to have a backup unit on hand regardless.