Rev Counter / ABS

My 96 model ES currently has two problems:
1 The rev counter is fluctuating. Think this is driven off the Alternator, if so, is it likely the Alternator output, or the rev counter itself?
2 My ABS light is functioning (on with ignition, off when driving), but the ABS is not working (two recent lock-ups on muddy roads causing near misses!). The only time I can feel it working is sometimes when cold when first gentle braking to leave my drive.
My mechanic looked puzzled when I told him, which is not a good sign.......
I am guessing an ECU problem?
Any help on the above gratefully received.......

Mine does this aswell, and the alternator is fine, its more to do with the wire on the back, if there is no heat sheild the exhaust manifold melts it and then it only works sometimes etc, jumps like a nut works fine sometimes... I will look at it when i am very bored.

The ABS... computers huh... damn them...

My 1995 es model had the same problems rev counter fluctuating and with the ABS not working know and then,with the rec counter measure the output of the alternator then slip the belt off and spin the alternator if its noisy the bearings are on the way out which caused my rev counter to play up,on the ABS I took out each one of the sensors in the hubs which is realy easy to do and clean them up and that cured the ABS problem

Not got ABS so cant help.
Rev counter - on the alternator you will see a single wire, this is the feed for the rev counter. Pull it off clean the contact and if need be crimp the spade connector so it fits tighter. Hey presto no more flicker.