This may sound over simplified but..... old battery cables corrode onboth ends so you have less amperage carried by the cables. (i.e. fewer strands of copper trying to carry more amperage than they are capable of. The next time you do a start cycle place your hands on the battery terminals one at a time and check to see if they are HOT to the touch. Also do the same thing for the chassis ground and the terminal lug at the starter. ANY hot terminal is a sign the cable has broke down either from age/vibration wear or corrosion. If you suspect the battery cables are bad get a VERY GOOD set of jumper cables (2 sets connected together if necessary) and do a direct from the battery to the starter connection. This is loads of amperage so be very careful and DO NOT do this alone. But, if the starter spins faster you have battery cable problems.

IF you have an external to the starter relay that too can cause the problem due to worn / defective contacts.

I will watch for any responses.

Thanks for using FixYa.

Kelly