Speedo problem?

[Goodwin]

Hi there. Looking for a bit of guidance from those n the know. I have a 94 Chimaera (pre serpentine) and occasionally the speedo and battery light misbehave. I can be driving along and the battery light will come on for few seconds then go out again. Doesn't seem to be linked to load/engine speed. It has been fine in traffic, at idle with lights on, interior fan going, and main cooling fans going but later in the journey will fligk on whilst driving down the road. The speedo behavior is completely normal.

Twice now it has stayed on after starting the car - and when this happens the speedo needle tays at max speed. (it normally sweeps to max then returns to 0). If I rev the engine a little both times the light goes out and once it goes out the speedo returns to normal. I have checked the tension in the drive belt and it is fine. Any other ideas please?

Thanks for the help.

[MADMAX2]

check voltage to the alternator and around the 100amp fuse on the chassis it may be corroded