Battery to Starter Relay size

[erikcroissant]

I am planning on running a #4 or #6 gauge wire from the alternator directly to the starter relay. There is currently a #10 wire running from the battery to the starter relay. Is there any reason this should be switched out for a larger wire? And what amp fuses should I put on the alternator wire/wire from battery? I am running a high output alternator with Holley sniper EFI system.

 

[twecomm]

Wire gauge does matter. You can't go wrong going with a heavier gauge. I would go as heavy as is reasonable. if you know what the average cranking current draw is of your starter is you can use this calculator to help decide a proper wire gauge for the plus battery lead. Also good to have similar gauge from battery neg to engine block ground.
https://www.batterycablesusa.com/voltage-dropYou
Ideally you want to minimize battery voltage drop to the starter. Here is a voltage drop calculator which can be used to calculate voltage drop.
Not sure why you need the fuse you mention. Do you still have an active factory "alt gauge" ? if so, the alternators output runs thru that gauge to get to the battery and needs to be of proper gauge to deal with your cars total electrical loads. Some folks bypass that path thru the bulkhead connectors for alt gauge. If you have installed additional non factory electrical stuff on your car wire gauges associated with alternator output will likely need to increase over factory wiring. Think you car would have a sacrificial "fuseable link" near the bulkhead connectors as ultimate protection between battery and the cars electrical wiring.

 

[72RoadrunnerGTX]

I am planning on running a #4 or #6 gauge wire from the alternator directly to the starter relay. There is currently a #10 wire running from the battery to the starter relay. Is there any reason this should be switched out for a larger wire? And what amp fuses should I put on the alternator wire/wire from battery? I am running a high output alternator with Holley sniper EFI system.

The described large gauge alternator to battery by-pass will also by-pass the designed circuit protection (fusible link) for the stock unfused wiring. Better hope you never experience a short circuit in the stock wiring with that by-pass in place.

 

[twecomm]

Yep...

 

[dvw]

Its all the same circuit. So the relay to battery wire needs to be the same gauge as the alternator to relay wire. If you leave circuit A1 B still intact the fusible link still is feeding the dash