Strange output problem with series/parallel blade pickups

Question

I have a set of APG T-sized blade pickups in my Tele. There's a set of two rails within the pickup similar to a Barden in design. It's wired with a master volume/tone, 3 way switch and a 2 way on-on switch that toggles the pickups between series and parallel. I've recently lost sound through the entirety of the neck pickup, and only the bridges humbucker sound is able to be fully utilized. Strangely when in parallel the bridge pickup only produces output through the A D B and e strings. The low E doesn't produce signal and the rest are very quiet.

I've taken a look at the wiring job from my last tech and it looks very professional, excellent looking joinery on all connections of the on-on switch, nicely adhered no big globs, no loose connections, though there are a lot of them, could be heat related. However I've heard that these variants of switches can fault out relatively quickly, or don't tend to last long. It is a switchcraft so not sure what better I'd find, but my new tech has suggested perhaps replacing a pot with a push-pull for the series-parallel but I'd really rather the sturdy metal switch.

Any ideas? Is the lack of output because of the switch, or should i be worried about the integrity of the pickups? (been told it's doubtful they've demagnetized, especially both not working apart from bridge) if it is the switch, what's my best buy when looking for a hardy switch for such a job?

EDIT: http://apgpickups.com/wp-content/uploads/2019/02/TBDT-Wire-Diagram.pdf This is the wiring diagram that was used.

Answer 1

This kind of problem is really hard to troubleshoot remotely but usually fairly straightforward to troubleshoot in person. Usually, the most effective approach is process of elimination. The exact method you use will depend on how familiar you (or your tech) are with electronics and different troubleshooting methods. Generally, to be thorough, it's probably best to start by identifying the problem rather than changing the configuration. Your tech seems eager to change the configuration - which is fine, if you trust him and you like the ideas he has, but there's a risk that doing so won't actually solve the problem. Not to mention, there's no reason why it can't work set up the way it is, if it's done correctly with working parts. Good techs will just naturally do function tests on each component as they work, though, regardless of whether they're changing configuration, wiring from scratch, or troubleshooting.

Here are the steps I would take:

• As a zero step, work the controls (switches and pots) back and forth several times, hit them with a quick spray of contact cleaner (with a paper towel tucked around them to catch overspray), and work them again. Make sure your contact cleaner is hitting the guts, not just getting sprayed on the outside of the component - pots and switches that are enclosed often have a little indent or vent hole that you can press the straw up against in order to shoot cleaner inside them. Sometimes, a dirty switch (even a brand new one) can cause all kinds of headaches, and simply cleaning it well will at least indicate the problem. Some new switches have anti-corrosion materials or other manufacturing byproducts left on their surfaces and they're scratchy or make poor connections until they've been worked a bunch of times or cleaned. Cleaning may actually solve the problem, but sometimes it'll just tell you which component is flaky and then you can replace that one. Sometimes it makes sense to do this clean-and-test procedure with the output jack too, but since your situation seems dependent on pickup and switch positions, it's likely not the jack that's at fault.
• Desolder both pickups from all electronics.
• Check each pickup coil with a multimeter for an appropriate resistance measurement. Depending on the pickup, you may get anything between, say, a few k and ten or twenty k ohms, but if you get anything much lower than 5k, higher than 20k, or you get a dead short, the pickup is likely at fault and you can replace it. Pickups are nearly bombproof but those that have been recently handled (i.e. just installed or they're on a pickguard that was recently pulled apart or modified) will sometimes have flaky partial breaks in the windings and can produce weird partial output like what you're describing. They'll usually show a weird resistance measurement to go along with the weird output.
• If the pickups test fine, connect each coil one at a time directly to an output jack. (You don't inherently need to use the jack in the guitar, sometimes it's simpler to use a spare jack that can be soldered directly to the wiring and left hanging just for the testing, to keep you from having to remove or reroute other parts). Plug it in to am amp and check for a signal. If you don't get sound, replace the pickup.
• If the pickups sound OK wired direct, you're left with the switches and pots. The most thorough testing method would be to desolder and test each component outside of the circuit with a multimeter but you may be able to spot problems by testing in-circuit first (a bad switch will usually show up in-circuit).
• Based on the wiring diagram you linked to and the description of your issue, it strikes me as the switches being the most likely culprit. I would start by testing the switches for continuity across the appropriate pins in each position. If that doesn't show an obvious problem, I would be tempted to use test leads to manually bypass the siwtches to check if the problem is resolved.

In most guitars, the pickups are the pricey parts and switches and pots are practically disposable - if you're paying someone to do this troubleshooting work, or you're not comfortable doing it yourself, it may end up cheaper to just drop in a new-off-the-shelf wiring harness instead of taking the time to test and replace components one by one - unless the components themselves have value, i.e. if this is a valuable vintage guitar with original pots and switches.