Hi and thanks for the repl
Yes, you are right about testing the wires using a tester, for domestic and commercial 110/240v applications you use what tends to be known as a "Mega", but everything on the circuit must be disconnected, otherwise the devices connected could be damaged, lighting cable being 1-1.5mm solid copper, ring mains 2.5mm, cooker circuits/showers etc thicker again, all with their own test settings, and one of the main requirements being of good insulation between the pairs/3 wires
Sadly a car tends to not have "disconnectavble" in the same simple way, ie the device is under the dash, or in the engine under the plenum, and there not being wire pairs, the negative being the chassis or anything else close to hand (the engine) so harder to apply such kit, but without doubt could be done, if you knew enough about the tester kit and the wire parameters, as the wire capacity is key. Cars have mnany more wire specs than a house uses.
Back to the reason for the tests
Yes to tes the alternator under load, not really for heat but to avoid the dirty noise generated by zenons and other items so that ac ripple can be looked at as cleanly as possible, using a carbon pile tester means hard to achieve identical load levels accuarately, and the risk of an untrained person overloading dangerously (600+amps possible!)
So a simple 20, 40-60amp load for idle and fast idle tests. This , subject to testing the rig once the resitive wire arrives, can now be done I hope fairly safely! (at a cost of about $15|GBP10), so a GBP1000+ Mega would be overkill, though might be more scientific if you knew what you were doing
The second reason was for smaller loads to be able to test circuits that had either intermittent faults, needed to be proved, or had delicate / unsafe devices, so a substitute load would make life safer, and easier to manage, fuel pump, F1 hydraulic pumps, wipers (lots of our cars can wipe with bonnet open)
The tests could either be done as a simple wiring test (either soak or normal), from the fuse to the device connection, with the subsitute load at either end, or as a working circuit with the substitute load at the device end, and volt drop being measured over time with the ability to see if it increased over time within the duty cycle of the device. (either by manual control/switching or letting the car do it)
This smaller load I have solved 9once tested!) the same way with a 0-100% dial with LED and using the correct length resistive wire to get a 10amp load, so I have a LED read out of amps 0.1-10amp variable load, and with a couple of 5 or 10amp on/off extra loads can create anything from 0.1-50amps. So the search for the how is over (I hope), now it's just a case of working out how/what else I can use it for!
The current 0.5amp load test devices just will not be enough load to show up a wiring fault for some of these in some situations, yes it will find a basic bad connection regardless of the operating current, so will find 85% or more, it's that 10-15% of wierd and hard to solve circumstances that I'm after. They definately have their place, still a bit risk in inexperienced hands as they can blow ecu's but a lot safer than a 50amp load or a carbon pile tester!
Had a look at the new PoewerProbe "The Hook" specs and it does do a "hot Test" load test, I assume it's 0.5amps, but that makes it one of the most complete single test tools out there, at GBP 400 ish, it needs to be, but I'll be ordering mine shortly!