MX5Ireland

have replaced it twice in 9000 miles still squealing ,waterpump and timing belt done the second time i replace other belt any ideas why its squealing

It probably just needs to be tightened up a bit.

when i have u ,when reving her hard above 6.5k the lights dim,whats that likely to be

If you have put in a new alternator belt, after a while it would need to be tightened up after it beds in.
If it's slipping then your battery will start to go flat, lights dimming etc.

all realated so thanks fergus as usual great help

Don't tighten it up to much though or it will wear out faster.
The middle of the belt should have a 'deflection' (distance measured when you push the belt up and then down - it's the gap measured inbetween).
1989 - 1993 = 8.89mm to 9.90mm
1994 - later = 6.09mm to 7.36mm

Hope that helps

huge help thanks very much