[Ruffy]

There appears to be some confusion about electrical behaviour here.

Originally Posted by glang

Look good but Id like to know how much less current they draw than conventional bulbs because of course this difference in power consumption will now have to be dissipated in the reg/rec unit so possibly leading to an increase in its running temperature......

Originally Posted by glang

on a twin headlight jobbie looks like about an extra 85w has to be continuously got rid of in the RR....

Nope, the reduced load will mean that the alternator won't produce the extra current at source. It's not the case that it will need to be lost in the R/R.

Originally Posted by Seeker

A motorcycle alternator runs at maximum output continuously (there are a few exceptions) - it has a permanent magnet rotor. The r/r takes what it needs and dumps the rest which is why they get hot, ...

This is potentially confusing and only partly correct - we need to clarify what "output" is.
A vehicle alternator is NOT a fixed power output device. It essentially drives voltage output, which is dependent on magnetic field strength, number of coil turns and speed of rotation. Therefore, in permanent magnet (fixed field) alternators the only variable is engine speed.
However, current output is dependent on load demand (within rating - current rating is determined by the coil winding cross sectional area and thermal design of the alternator to get rid of coil losses.)

Originally Posted by Seeker

the more load that is placed on the alternator's power, the cooler the r/r will run.

No. Heat is generated in R/R is primarily dealing with ac to dc conversion and managing over-voltage from the alternator, to keep max regulated output at c.14V. (A vehicle electrical system is supposed to be a constant voltage system.) It's generally to do with the type and configuration of semi-conductors in the R/R. Lower current load demand reduces heat generated in rectifying diodes while converting ac to dc.

Originally Posted by Seeker

If you exceed the alternator's output by adding too many extras, the best that can happen is a flat battery, the worst is smoke.

Likely you will eventually burn out the R/R or the alternator coils, if you ignore earlier symptoms of poor operation.

Originally Posted by Seeker

A car alternator has a field coil (instead of a permanent magnet) whose magnetic field strength can be adjusted to reduce the alternator's output when the demand is low. The early Hinckley Triumphs used a car style alternator but they are bulkier.

Some older Jap bikes also have wound field coils e.g. my 1987 Yamaha FZ600 has a slip ring rotor for field and a static stator for output, along with a 7-wire R/R rather than a simpler 5-wire design for SVs. It is true that reducing field strength is good for reducing voltage output. Current demand remains essentially a function of load though.

Originally Posted by Seeker

Ideally, the high current devices should all be on relays so low power through the switch gear and the lights (for example) are on a separate, fused supply from the battery.

I agree it can be helpful to separate low power control circuits from high power load circuits using relays. Ultimately depends on the rating of the switchgear though. Motorcycle switchgear tends to be ok when new (hence why manufacturers don't add in the complexity of relays etc.), but soon suffers once any sort of real world deterioraton occurs. Hence older vehicles often struggle with poor operation or burning-out of electrical switches or connectors. Cleaning contacts regularly or adding better power wiring/relays is the only way to avoid future burn-out and replacement. (This is probably relevant to the principal enquiry from OP.)