TZR250 tach reads low, no lights

[MuffTZR]

Hi all,
First time member long time lurker! Hopefully some friendly and helpful person who knows a wee bit more about electrics can help me out here with a problem I'm having on my 1987 TZR 250.
A couple of nights ago I was about to head home from work, got about 20 meters down the road when my headlight died. Turned back expecting to find a blown fuse, but all were OK. Rode the bike home the next morning and noticed the tacho reads about half revs. The lights are very weak indeed with the engine running, and don't work at all without it.

At first I thought this would be the battery, so I took it out and put it on a charger, straightaway indicated "charged". Checked with a multimeter -12.8 colts.
I thought that was strange so hooked it back up and tested again, now 4.5 volts. WTF?
Checked it with the bike running, no change (4.5 volts). Even high revs don't lift the volt count.
I've checked and cleaned every accessible electrical connection on the bike, so now I'm thinking it's either the altenator or the voltage regulator in need of replacement. Any other ideas? Any quick way to test which?
Thanks heaps in advance!!!

[del-solider]

Hey mate, you could try the guys at http://www.tzr250.com/forums.

They no there stuff when it comes to tzr's.

Give them a try could just be a common fault?

[gammaguy]

put in a new battery and then check the charge rate.if it is still low,it will be the regulator/rectifier.

[CookMySock]

Disconnect the battery from the bike.

Measure battery voltage.

Put on charger - note time to full charge.

Take off charger, wait 10 mins. Measure voltage.

Reply here and post battery voltages and time as above.

Steve