Hi guys, my car came home on a hook Thursday. It was an ignition problem. The 10-amp fuse that I put in- line to the MSD 6al box failed. I have a few other problems with the high voltage electrical system and I'd like to clean them up at the same time. Can you guys give me some advise?



1. It looks like MSD does not want a fuse in the line. How are you guys protecting the wire from shorting out without a fuse? Some posts are suggesting no fuse others are recommending a 30 or 40 amp fuse. What are you doing?


2. Any thoughts on why the fuse blew? A number of posts suggest that there is a voltage surge when you shut the MSD off and this surge can blow a fuse. However, I was pulling out from a light and was in second gear below 3000 RPMs.


3. I ran the power wire from the lug on the starter to the MSD box. According to MSD the wire should come directly from the battery. From other posts this appears to be to dampen the voltage spike from the MSD box on shut down. Can I use the 8830 capacitor to dampen that spike or should I be running directly from the battery?


4. The MSD box is a 2006 model with less than 2000 miles on it. The car will hesitate once after a hot start. The car runs great if started cold, until I shut it down. If I restart it hot, I drive about 200 yards and I will get a split-second miss or shutdown. After that the car runs great until I shut it down again.


5. I have an MSD 8572 distributor. Is there any way to modify this distributor to run without the 6AL box?



Thanks for any help you can give me.

Greg

 

I have my MSD box wired straight to the battery without a fuse.(probably dumb). I tried to wire it to the starter lug when I first installed it and cooked the box upon the first start-up. Thankfully Summit has a good return policy. I've never had a problem in 10 years after hooking it to the battery.(knocking on wood right now)

 

sell the msd pieces.
assuming your car has mechanical tach, get a top quality tach-drive HEI from Davis Unified Ignition aka DUI. If you require chrome dist shield-box, Retrofit 75-77 shield.
DUI is dead nuts reliable. If the DUI ever fails to fire; you can get replacement parts at FLAPS.

 

Can I ask how you fried it? Was it electrical or did it overheat? I have mine mounted in the passenger side fender well and am concerned about overheating. I have a real short wire to the box from the starter battery cable and it probably can't short to anything to begin with and it it does, it probably won't start a fire since there isn't much to burn there. If I do run it back to the battery though, and if it does short, the whole wire will get hot. Maybe a fusible link is the right thing here?

 

That's just **** poor engineering on MSD. That's why I got rid of mine years ago. They said under hood heat kills them.

So I went to a great ignition box that has water proof jacks so you can bypass it out of the system if you suspect a problem. But it never has.

https://www.summitracing.com/parts/f...RoCWCAQAvD_BwE

 

My MSD programmable ignition box is wired to the starter battery lug. MSD recommends this as an alternate method. Not sure why some folks think it needs a fuse. MSD doesn't think so or they would have put it in there. They do recommend lower gauge wiring be used if the wire run is longer than what came with the box. Mine has worked fine but not a lot of miles on it.

 

I've run a 6AL box in the passenger front wheel well right next to the windshield wiper washer jug behind the coolant overflow tank without any issue for 20 years which is probably a little over 25,000 miles. Heat, cold, rain, shine, you name it's been through it. In fact it was my daily driver from 2017-019. I ran wires directly to my battery without a fuse.


I did find this:

Holley Forums 6AL with blown fuse

 

Your wire run for the MSD should be covered by some kind of fuse. Mine, at least, is ultimately behind a fusible link. If this wire were to get cut and short somewhere, I wouldn’t be dealing with an electrical fire.

 

Mine just failed from heat and left me stranded. It was phony plug in rev limiter moduals and it didn't work very well for accuracy. It was under warranty and I just threw it away. They said to mount it in a cooler place. But Vegas is over 100 for 3 months straight

 

My engine management system requires the CD box, or I wouldn’t have it. So far so good with it mounted under the nose.

 

Is this an old analog 6AL or the newer Digital one?

Jebby

 

For some reason it is not letting me post "quote message in reply"
From Shark Racer
Your wire run for the MSD should be covered by some kind of fuse. Mine, at least, is ultimately behind a fusible link. If this wire were to get cut and short somewhere, I wouldn’t be dealing with an electrical fire.
That is what I thought too, but It took out a 10 amp fuse is about 1200 miles. Looking at other posts, others have suggested a 30-40 amp fuse, but I am not sure that is small enough to protect the wire in a long term overcurrent. I have the fuse holder installed so I think I am going to go with a 30 amp.

From Resdoggie:
My MSD programmable ignition box is wired to the starter battery lug. MSD recommends this as an alternate method. Not sure why some folks think it needs a fuse. MSD doesn't think so or they would have put it in there. They do recommend lower gauge wiring be used if the wire run is longer than what came with the box. Mine has worked fine but not a lot of miles on it.
Thanks. I missed that. I try to find info on the web before I waste others time answering something I should have found. I went to several sites, but not back to MSD. Any thoughts on the capacitor? Supposedly the power surge on shutdown is what blew the fuse. Only problem I have with this theory is I was in second gear, below 3000 RPM (3 amps) when the fuse blew.

Ebbenflow and GSkull Both suggested going with a different system.
I would like to go back to points but it doesn't look like I can modify the MSD distributor. I don't think I changed the point in my 69 since the 1980's and it still starts and runs good enough for me.

The andies showed pictures of his mounting
I have mine mounted a little lower in the fenderwell. I will get a temperature on the box the next time I run the car.


Thanks Guys.

 

I think it is the older analog. I believe it was purchased in 2006 by the PO when he could not get the engine to run right. Turned out the engine had three wiped cam lobes. I bought the car not running and he gave me a dual point dist with it. The dual point does not look like it is GM and does not have a vacuum advance so i don't want to use that.

 

This may help, MSD wiring diagrams and tech notes:

https://documents.holley.com/techlib..._wdtn_2014.pdf

 

Who recommended a 10 amp fuse? That box could draw about 1 amp/1000rpm. . How does the car run without the fuse? Is there anything else on that circuit? Has that wire's insulation rubbed on a grounded surface.
If the box hasn't failed, there's no way to blow that fuse unless there's something in the wiring.

 

I put the 10 amp fuse based on the 1 amp per 1000 RPMs number. I blocked the engine at 6000 RPM or 6 amps

I wired the MSD box directly to the starter lug so it is on its own circuit. Not sure of your 1st question, but the car didn't run after the fuse blew. No there is no rubbing or bare wires/rubbed through wires. The MSD box was on its own circuit and the wire is about 10" long between the starter lug and the MSD box.

There was an article I found that claimed on shutdown the MSD can backfeed a 450 to 500 V spike and that can blow the fuse. This is why I asked about the capacitor to blunt that spike.

 

I have 4 vehicles with MSD. Every one is directly wired to the battery. without any fuse. I've never had a problem. Have you called MSD?

 

I agree….the 66’ in the Avatar had a old analog 6A box and my 72’ has a analog 6AL…..both are wired direct….both in the right fender well like pictures above…..both solid as rocks…..
The Digital 6 boxes are much more touchy to voltage spikes but it has to be a pretty big spike…..
As far as I know….both have circuit protection…..
If you are having issues, do not overthink it….send it to MSD to have it looked at for free…..
The 8572 cannot be converted to Ready to Run….
Get a ready to run and sell your stuff if it bothers you….they are pretty reliable too….

Jebby

 

I thought they were internally fused. I'm connected straight to the firewall lug between my kill switch and the starter. Note that the battery IS an enormous capacitor.

 

Yes they are. The only reason you would fuse it is to protect the wire. Not sure if a fuse is the solution. I have used fusible links, they aren't as sensitive.