20 amp alt? are you sure, they'd have to be 45 or 55 amps

got a volt gauge/mulit meter?

i don't know, your the mechanic, i work on computers.... don't they teach that shit anymore or is it just oil changes & R/R parts now days?

Remember, the alt, and all the electrics run at more like 14.4 Volts when the car is running, not 12...

Remember that when the engineers at suzuki designed the electrical system, they didn't design it for 130W spotties or any other form of upgrade, so if you start loading up the electrical system, sooner or later your alt is gonna reach the limit of what it can power...

have you looked into doing the 110amp falcoon alt upgrade?

it's a dead easy upgrade btw

This is true. but do the electronics actually get the 14.4V? I didn't think they did.

Even at 14V, powering that many lights should be a concern, yet people are doing it presumably without alternator upgrades.

I'm thinking it's more likely my maths fails up there...

Remember, the alt, and all the electrics run at more like 14.4 Volts when the car is running, not 12...

Exactly the same on the 1.6 as the 1.3?

Remember you've got your battery in there as well and you don't run at full load all the time.

I.E. you go for a drive at night and are running under full electrical load. so you take your 37 amps for the lights (i'm lazy) and then your other load (ignition + stereo e.t.c)

Now, if this is over the 45A produced by your alt (at the 14.4 it produces) then instead of being able to power your car and charge your battery, it will be unable to supply enough current and without doing any calculations I think the voltage drops to battery voltage and the battery starts supplying current as well.

So you can think of it like a water tank. You put the hose in for an hour in the morning and an hour in the afternoon (driving in the day with bugger all load so you're charging your battery at a high rate) then, you go for a drive at night under full load which is like turning the tap on at the bottom of the tank.

Now, as long as the amount of energy you're putting into the battery (daylight driving) exceeds the amount you're taking out (nighttime driving + starting e.t.c) then your battery will stay charged and you won't notice. Until you go on a long trip at night and you're using energy from the battery (because you're well over the alternator output) and you're out long enough to drain the battery.
Now, if you did have this happen and things started to dim, Ideally you'd turn the lights off immediately and this would stop the car from stalling, I don't think you'd get much warning though.

I'm only a normal sparky not an auto sparky and I just woke up, but that's the basic theory of it.
SHORT VERSION You have a system with a storage device and a fixed input. If you take more out than the input then you are removing energy from the storage device, if the output drops below the input, you start topping up the storage. If the output stays higher than the input long enough, you will empty the storage device.

If I've confused you let me know, options are increasing the input (upgrading the alternator) which is the best fix.
Increasing the storage capacity (running a dual battery, which is a bandaid fix to give you a longer overload time).
Decrease the output (turn off the lights :p).

Ideally you would change alt's and run dual batteries but that's more expense! If you're super worried you've overloaded it, find someone with a dc current clamp meter and run everything while measuring the current draw on your alt + battery.

Good luck with it.