Think the bridge ground wire has disconnected on my Harley Benton SG Custom

Dave_Mc

Hi everyone,

I think the bridge ground wire isn't connecting any more on my Harley Benton SG Custom- I'm getting a loud hum (which disappears when I press the instrument cable in tight- it does this on other guitars too, except it's not as loud hum and it also disappears so when I touch the strings!), and I tested continuity and I'm not getting any continuity between the strings and the instrument cable ground. I'm getting continuity when I touch all the other metal parts and ground. I'm getting sound ok when I play the guitar, just the hum is the problem.

What's a bit strange though is that the bridge ground wire still seems to be connected to the bridge! Light tugging (I didn't want to pull any harder in case I did actually detach it) suggests it's still attached to something at the bridge/tailpiece. I've done a lot of pickup swapping on that guitar recently (I think the hum started with the first pickup change, though, and it was slightly worse or slightly better with some pickups than others, but still always there), so I also snipped the bridge ground wire (in case I'd broken/melted it) and stripped it back an inch or two, but I'm still getting no continuity even when I connect the multimeter to the strings and the end of the bridge ground wire. (Of course, I could have broken or melted the bridge ground wire before where I stripped it!)

Any ideas? I've read that a backwards-wired jack socket can sometimes cause the hum, but (and I could be wrong here) presumably that wouldn't affect continuity from the strings to the bridge ground wire? I didn't try rewiring the jack socket (I haven't touched the jack socket's wiring), but I did take it out for a quick look and it looked to me like it was wired correctly (but I could well be wrong!).

It has gold hardware, could that be it? I've seen some Youtube videos where someone was saying that on some of the Harley Benton basses with black hardware, the bridge ground wire wasn't actually making electrical contact because of the bridge finish. But that wouldn't explain why it was working originally- unless it was a bit of an intermittent connection I guess.

I did kill what was originally the bridge volume pot (and IIRC the bridge ground wire was attached to it)- it may not have been actually broken, but after wasting too much time troubleshooting, I just put in another (working) old pot from another guitar of the same value/taper/size which was lying around and which was a quicker fix. (I've converted that pot to the middle pickup volume now, and moved the neck volume, as that suits me better since the bridge and neck volumes are now where they'd be on a 2-pickup Gibson-style guitar- I doubt this has anything to do with it, but I'm mentioning it just in case it does! The hum did start before I killed the old volume pot and put in the new volume pot and moved them around.)

Thanks for your help everyone,

Dave

ICBM

I assume you mean buzz and not hum .

If you get continuity to all the other grounded metal parts but not to the bridge, tailpiece or strings, then the ground wire is not making contact even if it appears to still be trapped by the post insert. Gold plating makes no difference, gold is electrically conductive.

The absolutely correct way to fix it is to pull the post insert out of the body, make sure the wire is poked firmly down the hole alongside it, and drive it back in, but this can be tricky and there is a risk of damaging the finish. There's a decent bodge though, which is to drive a long and fairly thin self-tapping screw into the hole in the control cavity so the tip of it bites into the post insert, then wrap a wire tightly around it - if you can find one of the right length you can do it better with a terminal tag under the screw head, but it needs to be exactly the right length for that.

Dave_Mc

Brilliant, thanks John (as usual!)

ICBM said:

I assume you mean buzz and not hum .

I assume so! It's just like pretty loud "noise". It sounds a bit like a P90 when plugged into a high gain amp when you're standing too close to the amp.

ICBM said:
If you get continuity to all the other grounded metal parts but not to the bridge, tailpiece or strings, then the ground wire is not making contact even if it appears to still be trapped by the post insert. Gold plating makes no difference, gold is electrically conductive.

LOL I just assumed it was cheapo gold substitute! If it's actually gold, you're quite right, it's a really good conductor! D'oh!

ICBM said:
The absolutely correct way to fix it is to pull the post insert out of the body, make sure the wire is poked firmly down the hole alongside it, and drive it back in, but this can be tricky and there is a risk of damaging the finish. There's a decent bodge though, which is to drive a long and fairly thin self-tapping screw into the hole in the control cavity so the tip of it bites into the post insert, then wrap a wire tightly around it - if you can find one of the right length you can do it better with a terminal tag under the screw head, but it needs to be exactly the right length for that.

Bodge sounds like a better idea, this is me after all. Some of the paint was getting a little flakey behind the pickups and pickup rings already, so I would guess there's a pretty good chance of damaging the finish, especially if I'm involved!

Any idea on the best thickness of the screw? I'll have to buy some so I might as well get the size which will work best. (When I get home I'll try to estimate roughly how long I need, probably safest to buy a mixed set of lengths just to be sure.)

Am I right in thinking that self-tapping are the ones which you don't have to drill for, you just screw them into the bare wood and they make their own hole? I'm guessing (can you tell I've never done this before? ) you put the screw slightly off to the side of the cavity leading to the bridge, and then screw the screw at a slight angle so it eventually meets the bridge ground wire cavity and touches the bridge inserts? Or do you want to avoid the other cavities completely? Or have I totally misunderstood and you actually put the screw into the bridge ground wire cavity and just follow the cavity to the bridge stud? (In which case I'm guessing the thickness of the screw depends on the thickness of the cavity?)

ICBM

Dave_Mc said:

Or have I totally misunderstood and you actually put the screw into the bridge ground wire cavity and just follow the cavity to the bridge stud?

Yes, exactly that - from the control cavity into the hole the wire now comes out of - you may have to remove the neck volume pot to get enough clearance. The size of the screw depends on the diameter of the hole, but probably about 3-4mm.

There’s a photo here somewhere, I think of a Les Paul Deluxe, where it’s been done already.

Aha, found it - https://imgbb.com/4mHXn3W

Dave_Mc

ICBM said:

Dave_Mc said:

Or have I totally misunderstood and you actually put the screw into the bridge ground wire cavity and just follow the cavity to the bridge stud?

Yes, exactly that - from the control cavity into the hole the wire now comes out of - you may have to remove the neck volume pot to get enough clearance. The size of the screw depends on the diameter of the hole, but probably about 3-4mm.

There’s a photo here somewhere, I think of a Les Paul Deluxe, where it’s been done already.

Aha, found it - https://imgbb.com/4mHXn3W

Brilliant, thanks John It'd have taken me ages to find that! (I measured the hole, it seemed to be around 4mm diameter as you said, and the distance to the tailpiece stud seemed to be around 45mm, does that sound about right? You're quite right about the neck volume, I think I'll probably have to take it out.)

Does it need to be a solid core uninsulated wire, or does it just connect to the screw a bit more securely? (Or maybe that's just the one that was originally there, I seem to remember my Gibson SG has something similar!)

Just out of interest, should I be getting continuity between the strings and the bridge and between the strings and the tailpiece/tailpiece studs? It suddenly hit me today that I should maybe check that.