What the Heck is a Shielding Can?

I get asked this a lot.  Most people have seen the wiring harness of a guitar before-usually because they want to go snooping around to see what makes the thing tick. It’s a natural urge for guys and maybe for women as well. Most of us took stuff apart as kids and only paid the consequences when we couldn’t get it back together and Dad was due home at any minute and his lawnmower was in 150 pieces on the garage floor because you wanted to see what the inside of an engine looked like. Or something.  While most of you have seen a wiring harness, it’s probably been from a solid body guitar like a Les Paul or a Stratocaster or an SG-guitars which are easy to put back together again. Want to see the harness on a 335? No you don’t. Go look for a photo on the internet. You do not want to take out the harness on a 335. Once you get the hang of it, it isn’t that hard to get back in on a 335 made after 1964, unless it’s a recent 59 reissue Historic. These have no cutout in the center block-put there by Gibson in 65 to make getting the harness in much easier. The harness on these early 335s and the most recent Historics has to be installed through the f-holes. This is something you might want to think twice about before your curiosity gets the better of you. Especially if its your Dad’s guitar.  Here’s 345 harness.

You can see that 3 of the pots have a cover on them. These are called shielding cans and their purpose is to keep the pots from being affected by various forces-like power sources, magnets and so on. Why only 3? Simple. The 4th one which would be the tone pot for the bridge pickup won’t fit in its hole with the can on it-it would hit the edge of the body. The ES 175 has 4 cans but not 335s/345s and 355s. Obviously, they didn’t do that much because having one missing didn’t seem to make enough of a difference for Gibson to move the holes to make it fit. I think the most valuable effect a shielding can has is that it pretty much tells you if someone has messed with the harness because nobody ever bothers to put them back on after they’ve replaced a pot. I’ve never seen a pot replacement with the can soldered back on. I’ve seen harnesses with 2 cans and 1 can because pots have been replaced. The truth is, its tough to get a harness through a f-hole and the cans make it even tougher because they are big-big enough to barely fit through and big enough to scratch the hell out the top of the guitar when you try to stuff them in there.  Wait a second-why are there 5 pots in this harness? There aren’t. The one with the green wires is the 6 way Varitone switch-remember this is a 345 harness. And that big silver boxy thing? That’s the choke-a transformer of sorts that’s part of the Varitone circuit. This big thing is why so many people remove them. While some feel they steal tone-we’ll talk more about that another time, the other reason is they weigh about half a pound. Fortunately, all 345s have the block cutout because it would be impossible to get all of this through the f-holes. I’ve replaced a 345 harness and will never, ever do it again. You think that lawnmower was tough to put back together? Don’t start messing with your Father’s 345. He will kill you where you stand.  So, don’t worry about the shielding cans. They aren’t really necessary and if they’re gone, don’t bother trying to replace them unless  you are going to pay someone to do it on your 58-64 335 or your 345.  And, to be clear, they stopped using the cans some time in the mid 60’s. My 66 had them. My 67 (the notorious blue Trini Lopez) did not. So, don’t make a big deal out of them unless you have a serious collector museum piece. Then, to be correct, one of them should be missing. If you see a pristine dot neck with 4 cans, then something isn’t Kosher. There are a number of videos on You Tube and around the internet that show you how to pull and reinstall a 335 harness. Watch one before you try it. I’ll do another post with all the tricks and find a good video to post with it.

4 Responses to “What the Heck is a Shielding Can?”

  1. Jonne says:

    Eventually also those canned pots will get scratchy. Are there any other way try to spray them clean than removing the pots and unsoldering those cans? I mean those holes where the leads go in looks very tight.

  2. OK Guitars says:

    You can squirt some pot cleaner down the shaft (make sure it doesn’t get on the finish). Then turn the pot a few times and do it again. I’ve had very good luck using that technique

  3. Jonne says:

    I’ve seen it done but heard mixed results. Does it help to lift the shaft while squirtin’ or does it only apply on CTS-pots?

  4. OK Guitars says:

    I don’t know if lifting the shaft helps or not. It seems to work without doing that but it probably doesn’t hurt to do it-maybe get the cleaner deeper into the pot.

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