installing msd box wiring question.

[midnightrider1818]

alright, im installing a box on my car but im wanting to fuse my hots. the 12 v direct battery source. and the 12v hot from ignition hot. i was thinking about going with a 20a on the one directly from the battery and a 10a one from ignition. what do you guys think i should go with

 

[Meep-Meep]

MSD doesn't call for a fuse so I wouldn't worry about it. The unit is not in a constant on condition plus a regular fuse may be too slow to react anyway. The box may (or should) have short circuit protection built in and the worst condition I can think of is shorting the coil output leads together, or maybe putting the coil + to chassis ground, which depending on the internal circuit may be the same thing as shorting. Even that may not be fatal since it's designed to drive a coil with a less than 1 Ohm impedance primary winding.

I'm no MSD tech but this is how I see it. The 12 V from the IGN works with the points (or other trigger device) to run the circuitry that switches the primary side of the coil. This part probably draws milliamps not amps since it's basically turning on and off a transistor that controls a big capacitor. The fat power wire primarily supplies the juice to charge the cap that dumps the pulsed 400 volts over a few milliseconds into the primary side of the coil. I'll add that it's important this wire gets a good solid low resistance connection or the box will not work properly if at all.

 

[69 Runner]

Please don't hijack someone's thread, then start your own on the same subject.

I believe they are internally fused

 

[63RedFury]

No need to.....