How do sti shifters work?

It' s full sheet .You can start with reloading the software with Fisps
You will need to Load Primary 8.10 and Secondary 3.30
Software and instructions can be found at:
http://support.startrac.com/index.cfm?fuseaction=software.Software
If this does not work it will require a complete new display electronics:
http://support.startrac.com/index.cfm?fuseaction=diagrams.Dia02b&typ=1&sty=1&srs=11&mdl=28&prd=1028&stc=1033&sku=9-7632-SUSAP0&dia=624&dlk=&wsr=&sid=
715-3604

There's a used pair on an eBay auction right now ending 6d 09h (Sep 21, 201101:52:54 PDT) that you might be able to snag for cheaper than a separate right lever. Wait til the last 10 seconds and bid ONCE. Leave time to confrm the bid.

http://www.ebay.com/itm/SHIMANO-SORA-8-SPEED-STI-3300-BRAKE-LEVERS-DUAL-SHIFTERS-8x2-8sp-/200651614761?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item2eb7c4aa29

There are other models, too.

My $.02: I'd take the opportunity to switch to Campi Ergo (also available on eBay). The brake lever is ONLY a brake lever so you don't have to tip toe around it when shifting and ALL CABLES are hidden.

Find a Local Bike Shop on your own. You know where you live and UK is not very specific.

Or do some more diagnosis/research.

Web search "shimano sti shifter repair" (or most other simplified questions) for resources.

"Upshift lever" could be either one since they both shift up or down.

I'd make sure it's a lever problem before embarking on that project. Is the cable actually being controlled by the lever?

A simple web search for "Shimano 200GS STI assembly" yields all kinds of resources.

Another good start would be http://www.shimano.com/

Other web searches like "how to.." work, too.

Any 9spd Shimano STI brake lever hoods will work. Do a search on the web for: Shimano 9spd lever hoods.

This is very difficult to find, if not near impossible. The one on Shimano's site is the best detail there is available to the general public.

The Tiagra STI shifters and all Shimano Shifters are not specifically designed to be rebuilt and are very difficult to put back together, I do not recommend it. You can do some basic disassembly and reassembly but a complete rebuild is very, very tricky. Some of the internal gear parts are not designed to come apart and go back together with standard tools.

What is the problem with your shifter that makes you want to rebuild? I would be happy to help you diagnosis the problem before you destroy the lever.

If it is new, contact Peg Perego for a replacement. If it is not new, you can upgrade the shifter to a better version. (I just upgraded the one on my kids' gator.) You can buy the upgraded shifter for $24. http://tigerimports.net/sunshop/index.php?l=product_detail&p=7095

The old lubricant has gummed up. It needs a good cleaning and relubrication.
"STI shifters gum up after years of use. I've had good luck with this method and since it's nearly free it's probably worth a shot--

"Get a can of WD-40 or a similar light solvent/oil solution. Pull the brake lever back to the bar to partially expose the shifting mechanism and generously hose down the interior with your solvent. I mean really get it in there from all directions, using the little red spray tube if possible. Let it sit for a while and then drizzle in some light oil like Tri-Flo or similar. Then wipe down the exterior of the shifter with some Simple Green or other degreaser (to keep the overspray off your hands).

"I've rescued two sets of STI-type shifters with this method. Hope you get your problem solved one way or another, because new Dura-Ace sure ain't cheap."
source: http://www.bikeforums.net/archive/index.php/t-83743.html

You can download an exploded diagram of the 7900 series STI shifters here:

http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/ST/EV-ST-7900-2874E_v1_m56577569830670749.pdf

You can reassemble them according to this diagram.

This most likely is due to a blown internal speaker which has shorted across its voice coil rather than becoming an open circuit. Bel/Escort now uses special "high temp" speakers which resolve any failing speaker issues due to higher temperatures. I assume that your STi is out of warranty. Yet, it will be worth it ($80) to have the speaker replaced and to have your STi flashed with the latest firmware which also gives the STi a true audio ramp-up rather than just the original slow or fast audio beeps to indicate the strength of the detected radar. The new firmware also includes slight performance enhancements, and includes better filtering for Autoscan mode. This latter enhanced Autoscan filtering makes the STi noticeably quieter while driving around town.