Msd 6al & Blaster 2 Problems Blowing Fuses

[jklaus]

I have a 1993 Ford Probe GT which I installed a 6AL & Blaster 2 about 5 years ago on.
It has been working fine for the past 5 years.
At that time MSD did not offer a wiring harness adapter for that application so I fabricated one myself.

About a month ago I started having some hesitation and couldnt locate the problem - checked cap, rotor, plugs, wires, etc. Wasnt a huge problem but annoying.

However it just died while I was driving today. Turns out the main 40Amp fuse which controls ignition and other interior items keeps blowing. The fuse blows when I turn the key to the run position, just before cranking.

I traced through the schematics for the applicable circuits and eliminated all but the igniton system.

When I disconnected the positive and negative power lead to the MSD 6AL box and the orange positive lead to the blaster 2 coil, the fuse did not pop.

I then reconnected the MSD 6AL box, but not the orange positive lead to the coil. The fuse did not pop at this point either.

Not sure exactly how to test a coil or an MSD box.
However I did use my ohmeter to check the coil. My ohmeter is old and not very precise, but I use it as a guide. I measured 2 on the 200 scale for the positive and negative input terminals and measured 4.5 on the 20k scale for the output terminal. I saw some technical specs for the Blaster 2 coil at 0.7ohms for primary resistance - would this mean between the positive and negative input side? If so my inaccurate ohmeter may say its in the ball park, or would that be way too far off? I believe coils change resistance with temp? Other spec I saw was 4.7k ohms secondary resistance, again close enough to rule out a bad coil?

I would imagine if there is a short in the MSD 6AL box then just reconnecting the box and not the coil would cause the fuse to trip - yes/no?
Would this reasonably lead me to believe the coil may be the problem?

But if the coil's resistance measures out okay, they could there be something else wrong with the coil or likely elsewhere?

Both MSD box and coil are located in engine compartment. Subject to high heat, but not excessive (no turbo). What is the estimated lifespan on these components?

All your help would be appreciated.

Thanks, Jeff

Since the coil itself is controlled by the MSD, it really won't have an affect on the electrical system. However, the 6AL might be the culprit if there was a problem with it. When measuring primary resistance on the coil, you would check across the positive and negative posts. Secondary resistance is measured across the coil negative and the high tension tower. Make sure that the heavy red and black wires from the MSD are connected directly to the battery and that the connections are clean and secure. We are currently working on a new harness for that setup which should hopefuly be available by the end of the year.

[jklaus]

So how do I go about checking whether there is a problem with the MSD box which is causing the short?

Thanks, Jeff

If there is a problem with the MSD, you would need to send it into our repair department so we can take a look at it.

[bill jones]

-Have you checked the full length of big red wire from the battery to the MSD box---to make sure it's not worn thru somewhere and resting on a grounded metal place?
-Five years is a long time to allow somehting to cut thru the insulation.
-The most amperage I've seen a an MSD6 use is well under 10amps but it's common to see 5 amps.

[jklaus]

Thanks for your comments Bill.
I may try adding a 10A fuse inline to the MSD box.
Perhaps this will let me narrow the problem further.

I eliminated all circuits and started adding back. I added back the MSD and the coil and it didnt pop any fuses?! Not sure what this means, perhaps a loose connection. I only removed the power and ground from the msd and the coil wires. Perhaps they were getting old? Although my other connections to and from the MSD I left in tackt(sp?)...

Again, thanks for your help specifically relating to amperage draws.

Cheers, Jeff