Rennlist's Technical Site has many detailed technical articles on 911and 964 classified into Engine, Body, Brakes, Electrical, Suspension, Transmission and Miscellaneous sections.  Mainly in .pdf format and of excellent quality.

Ken Tubbs' technical pages have some great technical articles relating to his 964.  Lowering, brake upgrades, engine removal, anti-sway bar installation. engine detailing, brake ducts, repairs. seat and harness installation, exhaust bypass etc. etc,
 

The 964 Registry has a fairly complete technical links page linking to:
Airbox Modification / UpgradeC2 / C4 Technical Page, Engine Removal, Muffler Bypass Pipe Installation, Porsche FAQ's (Several 964 Articles!), Pelican Parts Technical Section, Porsche 911 Do It Youself (DIY), Porsche 911 Technical Index, Porsche964.Com Technical Section, Porsche Options Decoder, Porsche Option Codes, Porsche 964 C2 Engine Removal, Porsche 964 Technical, Tubb's Porsche Technical, Type 911, Tech Tips Dispersed thru Parts Sections, 964 Rear Wing Installation, 964 Valve Adjustment , 964 Distributor Belt Repl., 964 Rear Blower Motor Repl., 964 Gauge Face. Replacement.

Stig provides a number of technical tips on his 964 Technical Page, Performance Enhancements, Audio Upgrades, Suspension Options, Car Care. Distributor Drive Belt, Distributor Caps and Rotor Arms, Alarm, Centre Console, Windscreen Wipers, Door Switches, Oil,Parts ,993 Exhaust, DME, Chip maps, Diagnostic Socket, HVAC, Wheels & Tyres, On Board Computer, Technical Library.
 

George Rochford has some great C2/C4 Technical pages where he discusses his hydraulic pump pressure switch replacement, door entry switches mods, rear deck emblem replacement, primary muffler bypass and superb paint job.  He also documents his Top End Job.

This 964 owner's C2 must be maintenance free if he has the time to Hotrod his floor jack!.  Click the jack to check out his paint job.
 

Some say that one of the main reasons to switch to the 993 is that the service costs are lower as it has hydraulic valve adjustment.  Yeah, some reason!!.  Well if you follow Brian Smith's instructions you can adjust your 964 valves yourself.

If your rear spoiler wall has a split here are instructions from Garey L. Cooper on how to replace it.  Note:  These instructions are for a 993 but the 964 is essentially the same.  Look out for incompatibilities though and then resort to the 964 Porsche docs if necessary.

Here are instructions on how to paint your brake callipers red.

The US Pelican Parts site has load of technical articles on the 911.  Many with pictures.

Technical Forums

Finally, if you have a problem with your 964 I can guarantee you are not unique.  Many questions can be answered by searching the archives of either the 964 SmartGroup or the Rennlist 964 Forum.  If you do not find an answer in the archives just post your question to the forum.