I have a 40Amp Output Alternator, probably a silly question, but am I okay to run a 50A or 70A cable rather than a 110A or 170A rated battery cable?

Cheers

Mike

yes, you will need to put a 40 amp fuse in too, to protect your loom.

a 40A alternator with 50+ A cable to the battery is fine,

and, no, you don't need to add extra fuses.

though do ensure the cable is flexible.

You can alternatively run the cable to the battery side main ring terminal of the starter solenoid, *don't use too heavy a cable as it won't be flexible enough, if you have an old style 3 blade block connector you should run a wire from each as the blades are only rated at 35 amps.

If you want to use a fuse you can use a 150 amp Mega fuse or Midi fuse on the main starter lead mounted in a holder close to the battery.

Cheers

you will still need the higher rated cable from battery to starter.

Yes, you need to use a heavy gauge wire from battery to starter but the wire from alternator to battery can be lower rated.