Another MSD 6AL Problem
 

Just got my car back from the shop and it lasted about 5 miles. When the engine builder hooked the msd up as it should with the orange wire to the positive and the black to the negative coil terminal the car wouldn't start. He then hooked up the white wire to the negative coil terminal and it ran fine but the tach was eratic. In the mechanics defence both wires actually black at the point where they are near the coil. I had just changed to a magnetic pickup distributor and had not cut off the white (black) wire. I drove the car about 5 miles it started to miss and then died. Now it won't run at all. I have hooked it back up the way it should be and it still doesn't work. I tried shorting the magnetic pickup and all I get is a sound at the 6al box but no spark. I have tried to coils. My question is why wouldn't it run when it was hooked up properly in the first place and yet it ran for a while with the white wire hooked up. I assume something is now shorted out. I wouldn't think it should have run at all with the white wire hooked up to the negative coil terminal. Could it been caused by an internal short in the MSD 6al box?

Thanks,

What distributer are you running. Actually, I would like to know what all of the parts are in your ignition system.

I have a MSD Billet Distributor, MSD Coil and a MSD 6AL box. It all worked fine before I took it in to the shop. When I got it back it was running good but the tach no longer worked right. I got 5 miles from the shop and it started to miss and then quit all together. I found that the white wire from the MSD box was hooked to the negative side of the coil and the black wire was not hooked to anything. When I talked to the fellow who did the work on the car he said he first hooked up the black wire to the negative terminal on the coil and the car wouldn't start so he hooked up the white wire and it seemed to work fine. I have now hooked everything back the way it was before I took it to the shop and it has no spark. I also ran the tests recommended by MSD and I don't get any spark but hear a noise at the MSD box when I short between the wires on the magnetic pickup wires from the box. I do have power to the red wire when the ignition is on. Orange wire is hooked to the positive side of the coil. Seems strange that the car ran fine for a few miles with the white wire attached to the coil and wouldn't run at all with the black wire attached. I now assume that running the car with the white wire attached to the coil has probably shorted out the MSD box.

Thanks for any help,

I can't help with the big problem but the erratic tach is quite normal. I had this unit on a previous Cobra and even with an amplifier fitted the tach had problems.

The white wire is used with a points type ignition for making and breaking the circuit. The spark is made when the white wire becomes ungrounded (points just opening).

White wire is not used for mag pickup ignition except for diagnostics. You can disconnect the mag pickup, and tap the white wire on a ground, and get spark from the coil.

The coil wires are polarized (+, & -), because the coil is polarized; + to the plugs, - to the block. (The engine may, or may not run with this backwards, but not very well.)

A conventional ignition runs 12 volts to the coil during start, and about 7 volts from the ballast resistor when the engine is running. A capacitor discharge (CD), be it MSD, Accel, Crane, or any of the others out there work by sending a pulse of about 480 volts to the coil. Several of these pulses are sent to the coil with the MSD multiple spark feature. These pulses, generated when the charged capacitor discharges, generate the spark in the coil. Most CD system coils cannot be used with a conventional ignition because the windings are different. (Although CD coils are interchangable. Accel, and Crane PS91 work fine with MSD.)

Anyway, my guess is that the MSD is damaged, or defective to start with. Get an RMA from MSD, and send it back to MSD Tech for an eval and repair or replacement.

I new the white wire was not supposed to be used with the magnetic pickup distributor. I had it hooked up correctly before I took it in to have the engine worked on and the the ignition worked fine. The tach also worked fine. When I picked up the car it was wired incorectly with the white wire connected to the coil and the black left unconnected. The car ran well but the tach did not work right. I assumed something wasn't hooked up correctly but it seemed to run fine so I took off to head home but only got 5 miles before it quite. When I got the car home I found the wiring was incorrect and hooked it back up the way it was before I took the car in but the car still won't start and when I ground the white wire I only get a sound from the box but no spark from the coil. When I asked the mechanic about the crossed wires he said he tried it first with the black wire on the coil and the car wouldn't run so he switched the wires and the car started right up. I had extended the wires from the box and had used black wire on both the black and white wires from the box so the mechanic had hooked it up correctly first but then assume he goofed and switched the wires. What I'm afraid of there is more than one problem. I assume the box was OK but the hooking up of the white wire to the coil problably has now burned out the box. I will call the MSD tech line on Monday and see what they say. Thanks again for your response.

Just wanted to let folks know I resolved the problem. I replaced the MSD 6AL box and everythings seems to work OK, includint the tach. I assume the box burned out because it was hooked up incorrectly.

By the way when I called the MSD tech line they had no idea why the car should have run at all with the white wire hooked up to the negative coil terminal. They also told me to send in the box and they would repair it for a maximum of $55 plus shipping. I will do it so I can have a spare.