Hi Geoff
Fusing both the positive and negative lines to the MSD is a good idea. However, there's no way that a 12 gauge wire can carry 60 amps at 12 volts. I'd be more inclined to go with a 15 to 20 amp fuse as that's about all 12 gauge wire can carry at 12 volts without overheating.
As for interference, the MSD filter is nothing more than a 26,000 uF 24VDC electrolitic capacitor. Make sure you get one that's rated for high temperatures. Caps like this can be purchased at most any electronics shops for less than $3.00. The MSD price tag of $25+ is ridiculous! The filter <ahem, capacitor> wires between the MSD and the battery -- positive lead from the MSD to the positive side of the cap, positive side of the cap to battery positive, same on negative lead. It functions as a voltage buffer.
In my installation, the filter <ahem, capacitor> didn't do any good. The MSD unit is interfereing with my amateur transceiver (144 to 148 MHz, FM mode). I've done some investigation and found that the noise isn't coming in on the power leads -- it's being received by the antenna (confirmed by using a handheld scanner). Apparently the MSD unit uses some sort of oscilliator that oscilliates near the 150 MHz range. Apparently the MSD unit isn't FCC Part 15 compliant. I've posed some questions to MSD Tech Support on this subject...still waiting on their reply.
So I'm stuck...it appears that I can't have both. I either run the MSD or do without my amateur radio, at least for now. Presuming I can't eliminate the interference, does anyone want to buy a two-week-old MSD-6A and Blaster SS coil?
-Mitch
> From: "Hausheer, Geoffrey" <geoffrey.hausheer@intel.com>
> Subject: DML: MSD ignition install
>
> Okay so I got an MSD 6BTM for my truck (yeah I've heard that people haven't
> gotten much out of the 6BTM, but I've heard some good things about it as
> well). anyhow, I wanted to add an inline fuse near the battery (so that I
> don't have unfused live power running around in my truck), and when I called
> MSD, they told me to put a 60AMP fuse in! But the unit only comes with
> 12-gauge power wire, which I figure somewhere between 1.6ohm and
> 3.2ohm/1000feet, and is rated somewhere arund 20Amps continuous-current
> (probably a bit less for the stranded wire). So does anyone know what a
> reasonable sized fuse for the MSD-6 series is? If I put a 60AMP fuse in
> there, it's basically like not having one, but I really don't need to blow
> the fuse while hauling down the interstate.
>
> As a side note, I'm getting a lot of interference through my amp (not the
> radio though) I remember somone asking about the filter (just a capacitor,
> right?), but I dunno if anyone ever said what the value was. If I knew how
> much power it could draw, I could probably size it myself (but obviously I
> don't). If anyone has any info on the filter, please let me know.
>
> Thanks,
> .Geoff
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