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The white and red wires will be hot, black will be cold. Typically speaking you'd wire them in series by joining the red wire (hot) from one coil with the black wire (cold) from the other. White (hot) will then go to the vol pot and the remaining black (cold) to ground.

Hmm, that's a bit odd. Guitar parts with 6-32 thread are usually UNC to fit vintage Fender.

Thread size is UNC 6-32 - https://www.allparts.uk.com/products/bridge-saddle-height-screws-for-bass-or-t-guitar-slot-head-6-32-x-1-2-inch

+1 Looks like it has a vintage tint to me. The neck finish on my Musicmaster is much paler. Couple of pics below for comparison

https://shop.ehx.com/category/parts-knobs-electro-harmonix/

Yes a bit of googling provides an interesting read! It would appear that a single string can't produce anything lower than the fundamental, but a combination of two notes can produce a tone lower than the fundamental of either. This is called a 'difference tone'. A good example is the power chord on guitar (root + fifth). Because these frequencies have a ratio of 2:3, they generate a difference tone with half the frequency of the fundamental (ie. an octave lower). Apparently this is why power chords sound so fat.

A 55-01 with NTMB preamp sold on BC recently so may be worth having a chat with the seller

Pickups are passive (I believe the same as on the BB414) so no problem on that front with switching out the preamp.

That's very interesting, thanks for posting!

According to this thread the correct size is a rather tiny 0.05" )

If they're out of phase you'll get a drop in output when both pickups are full on. What's the volume like with just the neck pickup or just the bridge pickup? Having a low output doesn't necessarily indicate a problem (unless it's stupidly low). If you can adjust the input gain of your amp to compensate for the lower output and get enough volume then it's probably nothing to worry about. What model of bass BTW?

Nice looking bass. The pot codes may help with dating. Some other dating tips here - https://www.beatlebassdealer.com/dating-hofner-serial-numbers.htm

There's a black Vista Musicmaster for sale here - https://reverb.com/uk/item/20655705-squier-vista-series-musicmaster-bass-black-1997? Unfortunately it's in Australia!

Yes, it's a Bronco with a replica Musicmaster decal from https://luthierdecals.com/

I love my Bronco. It's well put together and with a few mods and a bit of fettling it plays and sounds way above it's price point. Mine has a Sentell Big Sis pickup (https://www.sentellpickups.net/bass.html), Hipshot Vintage bridge and Hipshot 3/8 Ultralites. Fabulous little bass!

I love Fralins. Have an early Lakland Skyline JO from 2002 when Fralins were fitted as standard. Fabulous bass. I notice that your box is marked +5% overwound so yours may sound a little beefier and darker than a regular set.

The chart is generic for passive tone. I think the frequencies shown are actually for a Jazz but the same principle applies to P and any other passive bass with a regularly wired passive tone control. The bump in the low mids when tone is fully down kicks in if one end of the tone cap is wired to ground. Some basses have a small resistor between that end of the cap and ground in which case you don't get the bump . Some G&Ls are wired that way.