No crank and relays in a w210 1999 E300 TD
 

Hello,

My E300 randomly "no cranks". All the lights on the dash come on but on the final turn of the key "no crank". It sometimes can take 2-4 goes to get going. We are looking in the direction of the battery, as its old, and the relay.
(Yesterday it started perfect every time!). This happens both on cold and warm start. More so on warm.

Firstly, would a weak battery cause this to occur randomly?
having located a bunch of relays beside the fusebox, they seem to be designated with letters on the relay board, A to G. Can someone tell me what each relays controls?

regards

barry