Today the alternator/battery light came on in my 01 blazer and the voltmeter was sat at 0, now the voltmeter has occasionally sat at 0 before without the warning light being on which I put down to maybe a sticky/iffy gauge. Is it likely that my alternator has breathed its last or is there something else that could be causing this like a charging relay somewhere? The reason I ask this is that just before I got home after the light came on the speedo suddenly went nuts bouncing up and down and several other warning lights flashed on and then it all went back to normal after a second or two.
Any help appreciated, it appears to be a one wire alternator so how do I test this, I have a multimeter.

Is it worth fitting an uprated alt as I am about to fit a load of extra lighting? Are they easy to remove, I've not worked on anything with a serpentine belt before (I'm guessing it would be a good time to change the belt as well) Mines made somewhat harder by the fact it has a load of extra pipes over the alt for the LPG gas (Propane) conversion

 

OK stuck a meter across the battery this morning and got 11.1V with the engine off dropping to 10.8V with the engine running so clearly the alternator isn't putting anything out. I had to drive it today to get the kids from school and all the gauages quit working, no speedo, rev counter, fuel gauge, voltmeter or temp gauge. Is this likely to be because the battery voltage has dropped too low? On the way home it started to hesitate a bit so thank god it did it just around the corner from home so I got it back. Trouble is I can't find anyone with an alternator in stock in the UK apart from the main importer who want wait for it, £164 + 20% tax ($316) for a new one and this is the kicker, £70 ($135!) for a new serpentine belt (the old one appears to be the original so needs changing whilst I have it loose. If I can work out which one I need I may have to order both from Rockauto. The main importer told me that although its registered as a 2001 its a 99 model year so do I look at the 99 page on Rockauto or the 2001 page? Did they alternators fitted change between then? Can anyone help me as I need this up and running asap. Even with international shipping and taxes a remanned alternator and a Gates belt is still not going to come anywhere near $415 thieving bastids.