Why have more juice on the alternator? Simple, when you add things like 40w per channel stereos, subs, electric fans, oxygen sensor, aftermarket ECU etc etc etc. you’re stressing a 40A alternator beyond its design intent.
The 40 Amps are sure as heck not there at idle and need say minimum 3k RPM to be generated - so on a wet night with the cabin heater fan going, stereo on, say rear screen heater (if it works) and / or front heated screen, wipers on, lights on (assuming non-LED) + electric cooling fan, you’re way over what the stock alternator is able to deliver at idle.
Now then to your points:
1. The ammeter and associated wiring is of course a fair shout. That is alternator upgrade 101 and why in TR / BL circles, high amp ammeters are available for such upgrades. But if you already have a voltmeter then I t’s a moot point.
2. Just because the alternator is able to deliver more, doesn’t make your accessories consume any more than they already do or need. Their resistance doesn’t change because you added more capability to the alternator. They all sit behind fuses anyway, so regardless of the alternator being capable of delivering 0A or 1000A, the accessory behind a 5A fuse or 40A fuse will still draw the same and the fuse will blow if there is a short. The wiring is already being burdened by the same amps so no worries about wires burning there or upgrades being required.
3. The only place (ammeter aside) where the wiring can be overwhelmed is:
A) a short before the fuse box - which frankly will still burn when you consider the battery will deliver 300+ CCA and 90Ah without the alternator even functioning.
B) the charge cable going from the alternator to the starter motor (then to the battery). The battery is the only thing that can draw more amps than the wiring is designed to deliver - but then again, that wiring to the alternator has a fusible link between alternator and the starter motor. So the link will blow before the stock wiring fries.
As you know from my posts, I didn’t get round to running my parallel cable when I fitted the juicier alternator and never had problems until a loose bolt from the back of the alternator fell into it and started shorting things. And even in that scenario, the fusible link blew first. But for 7 years before that, it ran perfectly OK with the juicier alternator and no extra cabling. Which of course is now remedied by running a 60A cable fused at 40A before the alternator, in parallel with the original wiring, allowing the battery to take max current from the alternator if required. Which it never has done and for that to happen, the battery has to be totally flat.
So back on track with the OP’s question: my preference would be to get yours rebuilt in the UK, as you would have “come back” and have a higher chance that quality parts are being used. Some of the reman stuff I’ve bought (not alternator) has been shockingly poor quality. And bear in mind RockAuto’s returns policy looks great on paper but either too expensive to return or they don’t accept the return as it costs them too much to post back. Ask me how I know
So if you’re worried about what the grumpy old men are saying, then have it rebuilt to stock spec. But you now know the logic as to why I went the upgraded route and would again in a heartbeat!
