T-40 Wiring / Controls / Tone Help

Hi All;

I recently got a T-40 off eBay and have noticed something odd about the controls that I don't remember my original T-40 doing. Here's the scenario:

Pickup selector on bridge pickup, knobs at 10. Great punchy, trebly sound. Roll the tone to about 8, and the tone fattens up in humbucker mode. Volume control works in a perfectly normal manner.

Pickup selector on neck pickup, knobs at 10. Great bassy T-40 tone. Roll the tone to about 8, and the tone is huge and fat. Volume control works in a perfectly normal manner.

So far everything exactly the way it should be.

Pickup selector on both pickups, knobs at 10. Everything still normal. Roll each tone knob to about 8, and the second coils kick in perfectly.

Here's where it gets weird.

With both pickups on, I roll the volume of the neck pickup down to about 8.5 / 9 and the overall volume gets louder, and very honky. Almost like the bridge pickup is kicked into over drive.

Roll the volume of the neck pickup all the way down to 0, and the tone is nothing like having only the bridge pickup selected. It's sounds as like the bridge pickup is muffled behind a pillow.

The same goes in reverse. Both pickups selected, turn the volume down on the bridge pickup and the overall volume goes up at about 8.5, and then it sounds like the neck pickup it muffled when the volume on the bridge pickup is at 0.

I would expect having both pickups selected with the volume turned all the way down on one would give the same, or close to the sound as just having the turned up pickup selected.

Is this behavior normal, or is there something amiss here? After a little digging, I've read that dirty pots can cause odd things like this. I'm going to try some cleaner, but thought I'd ask the group as well.

It could be dirty pots. I wonder if the wiring has been modified from stock?

Thanks for your reply! From your comments, I gather that it's NOT normal behavior.

When I originally got the bass, someone had replaced the pickup selector switch with a completely wrong switch and botched the wiring.

I ordered two new switches from digi-key (per your suggestion in a different post, thanks for that) and took it, and the wiring diagram i got off this forum to a luthier / long time friend to set things right.

I've got a new pickguard coming in the mail, so when I've got things apart to replace that, I'll double check the wiring and clean the pots.

Sounds like you got a handle on it. Hopefully when you get it back together you'll find the problem is gone.

Thank you again for your replies. I'm hoping I could ask another question before I get to annoying.

I've got the wiring diagram and am checking it against what is going on in my T-40, and there are some slight differences in what appears to be the grounding.

Does it make a difference which pot a wire is grounded to? The diagram has the bare wire from the bridge pickup grounded to the back of the bridge volume pot, but mine is connected to the bridge tone pot. Does this really make a difference? They all seem to be connected in one big loop.

Also, I see that the switches should be grounded to both of the volume pots, where mine don't ground at all. But I can't tell where the wires are connecting to the switch. Do they just connect to the side?

Thanks again for all of your help.

Ron

I really don't understand wiring and the idea behind all of it. I do good to follow the diagrams and get mine back to stock. I really don't know if those differences yours has would be a concern or not. Hopefully someone with a better grasp of wiring can pipe in and help.