Lighting electricals - Ghost in the Machine

Now that I have my Series 3 on the road there are a few strange things that are happening with the electrics, this was very true this evening when needing to use the side lights before lighting up time because of the weather..

When I turn on the side lights both the indicator 'tell tale' lights illuminate, they do not flash and are on dim, not sure if this is a correct thing with a Series 3. What is somewhat stranger is that once the side lights are turned on the fuel gauge starts to rise quickly as does the temperature gauge, they go from mid levels to nearly high within 30 seconds so I don't think this is alternator draw causing engine heating as it wouldn't seem likely to happen so quickly.

Now the behind dash stuff has been chopped about in its life and things like the display illumination does not work so all of these strange things do not really surprise me but I'm racking my brains on why turning on the side lights would cause both gauges to rise so quickly like they do (and the tell tales lighting IF they are not suppose to)

The problem with the indicator lights sounds like an earth problem, probably at the front or rear of the vehicle, sounds like some of the sidelights current is returning to earth via the indicators and tell tales.
Guages are diffo, theres a regulator behind the clocks on a spring clip, the wiring to this might have been screwed with.

There's a good drawing of what colour wire should go to which contact on the back of the dash in the manual. Sidelight problem does sound like a missing earth at one of the lights but the gauge misreading is a bit odd, sounds like the sidelight circuit is connected to the regulated side of the regulator.

After much rewiring and correcting things that have been messed about with in the last 30 years I have managed to get things nearly back to normal, thanks for the suggestion of looking at the voltage regulator as this had a connection that was intermittent.

As always, great help from fellow forum users.