22-11-2019, 05:04 PM
Thank you for the advice - finally had a quick measure of voltages, but the garage is cold again today.
With an analogue voltmeter, the battery reads just over 6 volts - say 6.1 - of which about 5v is reaching the o/s headlight bulb contacts with the bulb removed, and the other light turned on. As would be expected, the removed bulb is brighter when connected directly across the battery, but I can believe that new bulbs might be even brighter as the old one is not dazzling. It must be at least 20 years old. The ancient bulb holder contacts are a bit corroded - no longer shiny.
I have not yet checked the earthing voltage drop or seen if a direct earth back to the battery helps. There is a return wire from the each light to a wing bolt. It looks as if there may be some corrosion of the wire where it is trapped under the nut - so this might be improved. The main earth cable runs from a bolt at the back of the starter motor to the positive battery terminal via a 'red key' isolation switch. However, there is no extra strap between the body and the rubber mounted engine. There is no measurable voltage drop across the isolation switch - this is not so old, being a replacement for the one that failed without warning a few years back.
When it warms up a bit, I plan to have a look point to point to see if the voltage drop is occurring mainly at a single location, or is accumulated through the various switches, connections and wiring.
Colin
With an analogue voltmeter, the battery reads just over 6 volts - say 6.1 - of which about 5v is reaching the o/s headlight bulb contacts with the bulb removed, and the other light turned on. As would be expected, the removed bulb is brighter when connected directly across the battery, but I can believe that new bulbs might be even brighter as the old one is not dazzling. It must be at least 20 years old. The ancient bulb holder contacts are a bit corroded - no longer shiny.
I have not yet checked the earthing voltage drop or seen if a direct earth back to the battery helps. There is a return wire from the each light to a wing bolt. It looks as if there may be some corrosion of the wire where it is trapped under the nut - so this might be improved. The main earth cable runs from a bolt at the back of the starter motor to the positive battery terminal via a 'red key' isolation switch. However, there is no extra strap between the body and the rubber mounted engine. There is no measurable voltage drop across the isolation switch - this is not so old, being a replacement for the one that failed without warning a few years back.
When it warms up a bit, I plan to have a look point to point to see if the voltage drop is occurring mainly at a single location, or is accumulated through the various switches, connections and wiring.
Colin