I agree that with a poor earth, it adds resistance to the circuit & the voltage across the bulb changes ie goes down. By Ohms Law, as the resistance of the bulb is fixed, as the voltage across the bulb goes down, so must the current decrease, it cannot increase. But the voltage across the whole circuit (wire + bulb + poor earth) is fixed by the regulator & cannot change. I don't see how the bulb could draw more current?
All 1-Ton Humbers have a 24 volt supply & of course all bulbs including turnlights are rated at & supplied by this 24 volts. However for improved reliability the turnlights on the Hornet are rated at 12 volts & supplied by a resistance fed from the flasher.
Sometimes I forget this, if a turnlight bulb is damaged, I have made the mistake of fitting a 24 volt bulb. The bulb glows dimly, it doesn’t glow to full brightness because feels it should demand more current. In fact when I have left a 12 volt bulb in place for a while it would seem to be less prone to blow.
This wrongly fitted 24 volt bulb doesn’t know why it has a reduced supply whether it is deliberate resistance or resistance through a poor earth.
I agree that wires around a poor earth will get hot & can even melt. The heat from the poor earth like any resistance is proportional to the square of the current times the resistance. This heat is at the point of the poor earth but will be conducted thermally along the wire feeding it, getting cooler the further from the poor earth. The bulb that it is associated will be no hotter because of electrical activity from within the bulb.
But as you say the practical points are to make sure you have a damn good earth & establish that you have the correct voltage from the regulator & see what happens to it after that.
PS I wrote all this waffle an hour ago, went to preview, wouldn’t let me preview, try to go back then whoosh its all gawn. So did this in Word then pasted it, not getting caught out again!
Computers ggrrrh :computerterror: