Grounding issues on Mustang with Hotrails + vintage rails

[Snowgal]

I'm helping my teen son with wiring a Fender Mustang and new Seymour Duncan Hotrails and Vintage rails pickups. Everything is working great except we have a hum which his clearly grounding since we touch metal and it goes away.

Two questions:
1. When stripping the wires (since Seymour Duncans are so LONG) I accidentally pulled the green and bare wires so they were a bit short. I soldered a new wire to the existing SD green and bare wires so it would reach the switch. Would this cause a problem?

2. I found a wiring diagram from SD that shows the bare wire being ground at pots and green at the switch. I grounded at switch. Would that cause a problem?

Thanks for any replies I get. I am a total newbie and learning as I go.

 

[Blille]

Is the bridge grounded? That’s more likely the culprit vs the pickups.

Maybe this helps https://www.fralinpickups.com/2018/11/12/understanding-guitar-grounding/

It’s annoying but you’ll figure it out.

Edit: welcome!

 

[Snowgal]

Thanks! Bridge is grounded. As far as I can tell, all ground wires are in place. Do I need to run a ground wire from one of the pots to the shielding paint?

 

[Mincer]

If the pot body is touching the paint, you don't need a wire. Test for continuity between the back of the pot and the paint.

 

[ThreeChordWonder]

Bare wires ALWAYS go to ground. They are the shield grounds, not the pickup grounds. Do NOT wire bare wires to a switch, ever.

Green wires, as grounds,, either go to ground or via the switch if your wiring diagram calls for that.

Bridge and body, both, should be grounded. You can run a wire from the bridge to a screw into the body, which must make contact with the cavity shielding, and then onto the back of a pot, if you like, but BOTH should be grounded.

A cheap multimeter with a buzzer that, um, buzzes, when you have continuity between parts helps a lot. About $15 at Home Depot etc.

 

[alex1fly]

One of the best practices I've seen and adopted recently is to connect every ground wire to the back of a single pot, and then ground that pot to the bridge and/or the shielding paint. That little extra consistency helps to eliminate variables.

Your lead extensions could be an issue, but if you twisted 'em together real good, got solder flowing all around them, and then used heat shrink or electrical tape to insulate the connection, you should be fine there. Sometimes the exposed wire portions can butt up against a component and cause issues.

 

[Nightburst]

First check the output jack, 9 out of 10 times it is either wired wrong or unshielded wire was used. This will act as an antenna and cause noise.

Make sure all ground connections go to one central point, anything different will cause ground hum (ground loop).
Check continuity with a multimeter on every component that should be grounded (anything metal basically).
When you are sure everything is grounded properly and you still get hum and it goes away when you touch the hardware, you need to shield all the electronic and pickup cavities and connect that to ground.

 

[Snowgal]

Thank you all, this is very helpful. I am a complete novice and have another question. I am working with two 3-way sliders. When testing with the multimeter, should I get continuity between output jack and each of the 8 poles on a switch?

 

[Snowgal]

A question about the bare wire: should I run it to pot to ground? If so, it will be running along side the switches so I wonder if I should tape off OR solder to a shielded wire or leave it bare?

 

[Nightburst]

you can leave it bare, the hot signal wires should be ideally shielded so the signal going through stays clean.
Just make sure you wire all ground connections to one central point. This way you wont get any ground loops, causing noise too.

 

[GuitarDoc]

Grounding is basically a simple problem to solve/eliminate. ALL components should be grounded...a wire from one pot to the next, to the next, etc, or all components wired to a central spot (pot). Electrically it makes no difference how you do it, just make sure everything is grounded.

Forget about "ground loops"...they just don't exist in guitar wiring.
Forget about "all ground wires to a central point", unless it is convenient. No harm in doing it this way but it may just require longer than necessary wire runs.
A switch SHOULD be grounded, just like any/every other component in the guitar.
It is best that ALL wires, including ground wires, are insulated. It is best that even the bare ground wire have heat shrink tubing or tape on it so that it doesn't inadvertently touch anything it shouldn't. Diagnosing a problem later on because of a ground wire touching another wire connection or lug will take ten times as much time as just doing it right from the start.

I make custom guitars and every one has copper tape shielding in the cavities and every component, including the switch and the bridge, is grounded. I NEVER get noticeable hum or ground noise from even high power P90's or single coils.