check and if required tighten battery terminals, check battery hold down clamp is secure and central on battery, check cable from battery- to where it connects to earth block this connection is prone to cracking due to vibration im assuming by playing up you mean engine cutting out also in engine bay there are other main power connectins check all are tight and secure good luck r dalton richard32110@googlemail.com may be able to help further
r dalton, January 2009