As time goes on, I've personally found those capacitors to cause more trouble than good. The horn cap failed, and the wiper caps were causing a slow wipe. I removed both of those and the horn/wipers resumed working correctly. I removed the cap off the alternator too. Given how advanced surveillance is these days, there's no need for these parts to remain on the truck. They already knew you were around when the glow plug relay clicked...
Caps do dry out and go leaky. This will certainly cause issues of they are not good.
I had to replace the caps on my alternators. The hash emanating from them rendered the HF and up into the lower portions of the VHF spectrum useless.
New caps made a big difference but there was still one more item causing a lot of RF noise.
The low coolant module was making a lot of RF noise, I unplugged it and all the noise disappeared.
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