Late '70s Strats do not have a fantastic reputation. They suffered from tuning problems, a three-bolt neck join which didn't work too well, and dodgy quality control. Our mission is to take a '76 maple neck Strat (modified with a tortie pickguard and unoriginal pickup covers), reinstall the original bridge pickup, put a useful tone control on the same pickup, clean up the rest of the electrics, sort the neck join, adjust the trem and make it play, and stay, in tune.
First, clean your working area, place a sheet underneath the guitar for protection and assemble all the tools close to hand. Take off the strings, and remove the scratchplate (hold your fingers around the bottom of the screwdriver while doing this - if it slips, it'll hit your fingers and not the paintwork). Also, disconnect the jack plug and the earth lead on the tremolo block; that way you can move the scratchplate away from the guitar to work on it and not get tangled up with wires.
With the 'guard off, we can see that this Strat has had some untidy work done on it in the past, so we'll re-solder some of the dry-looking joints. Bad joints are the ones that look like the solder is in lots of little bits, rather than a smooth, flowing pool. Bad joints are usually caused by not heating up all surfaces - a meaty 35W soldering iron should cure this.
It's vital to ‘tin' everything - not just the surfaces, but also the actual wire - with a thin layer of solder before you actually try to solder them together.
On old-style Strats the neck pickup has a tone control, and so does the middle pickup. The bridge unit has none, but all you need to do to fix that is a simple bridging wire.
A five-way US Strat switch like this has four tags on each side; taking the four tags nearest the pots, you need to solder a wire between tag 4 (furthest away from the pickups) and tag 2. Turning down the middle pot will now affect the tone of both pickups, but that's no problem since the standard switch layout means you can't have both on at the same time. That done, we'll tidy up the iffier-looking remaining soldering joints, and spray some switch cleaner into all the pots and the switch.
Before replacing the scratchplate we need to resolder the jack plug - clean it first with wire wool - and the earth connection on the back of the tremolo spring plate. This last one is a big piece of metal and takes a lot of heating up; not enough heat, and you'll end up with a dry joint and bad earth problems.
Next, the bridge.
Take the saddles off, remove the inevitably dirty and corroded little grub screws, and soak them in WD40 for an hour before cleaning them out using a small drill or sharp point. If the grub screws aren't clean, the tiny Allen key won't fit right and you'll end up rounding over the inside of the hole, making it hard to adjust them.
Strats from '71 to '81 had a three-bolt neck join incorporating a Micro Tilt device. Because the Micro Tilt system is metal-to-metal it made the neck join very easy to move, which in turn allowed the neck to shift if any undue sideways pressure was applied to the neck, which of course will ruin the tuning.