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Message: <blockquote data-quote="shovel" data-source="post: 1589294" data-attributes="member: 29855">The battery (constant) side of the ignition coil is connected directly to the power supply of the PIP (hall effect sensor inside the distributor) and the TFI module.   Every time the coil fires a surge of flyback voltage gets dumped into the primary coil and feeds back into the electrical system. Ultimately the battery takes up that surge because it has very low resistance but the wires, fuse and connectors between the battery and coil do have some resistance which means there's still quite a bit of noise (fluctuating voltage) at the coil end of the circuit.  Any voltage differential across a semiconductor resolves as heat whether it's doing a job or not so that noise is heat and heat kills.  So the capacitor lives as close to the coil as possible and provides almost infinite resistance to DC voltage while approaching a short circuit to AC noise.  Whatever noise it eats doesn't feed back into the PIP and TFI so they stay cooler and live longer. On 5.0 SN95's this cap is electrolytic - it's basically a little taquito made of mylar and rubber soaked in gatorade.   The gatorade leaks out over time,  typically 10-12 years is expected.   In a hot environment like the engine bay especially there's no such thing as a 30+ year old noise cap that's still in business.  You can replace it with another OEM one like that or you can get one made for a newer car that looks like a black lego croissant and replace its connector with yours.  You just cut the wire on your old dead one, cut the wire on the new one, solder them together with some heat shrink and you're in business.  Don't use those "solder and heat shrink in one!" things.   The newer noise filter caps are dry and have effectively unlimited lifetime.  [ATTACH=full]50353[/ATTACH]This is the newer style of noise filter cap on almost any "coil pack" vehicle from the 90s-00's.  If you need a specific model it's any 99-04 mustang.  Here's a diagram showing where the cap lives in relation to the coil, PIP and TFI module.  [ATTACH=full]50352[/ATTACH]</blockquote>