I've got a VL Berlina, which has been sitting in the shed for the past year due to my loss of licence. I've done a great deal of work to it, though now I've run into a little problem. I've got 3 gauges mounted inside all running perfectly, though after I hooked up the air/fuel ratio gauge, a little problem became visible. I've got all 3 gauges getting their power from the one ignition wire-- the one wire that supplies the igniton power source. They all read fine and work fine, though as soon as I turn my headlights on, bang, the air/fuel ratio gauge dims so much that I can't even see what it's reading. When I put my foot down, it brightens back up, though once I let my foot off the pedal, it dims back down to nothing. My earth connections are perfect (to the chassis), and my signal wire connections are soldered. Now I just wanted to know if this problem would be related to my wiring, or would the alternator be on its way out? Could the gauge not be getting enough power? ...I'm hoping its the alernator playing up, because believe me, it'd be easier for me to change that then to muck around with my wiring again. Help me out, I know it's only a little problem, but it's got on my nerves and I can't look past it.

You may have taken the power feed from the line feeding the headlights, so a large current pull on that drops the voltage and/or the wires are corroded somewhere so they cant carry as much current then suffer from larger voltage drops. The only real place to take off the ignition feed is from the fuseblock, the positive side positions 10 to 12, not from somewhere else down the line etc,

So I can run an igniton feed from the positive sides of fuses 10 and 12? I didn't know that, I thought it'd affect the fuses or something else or whatever, seems to be that if I do something right something wrong always comes with it lol haha. Ill try it out now, thanks.

Fuses 10 to 12 are bussed as common and only come on when key switched to ignition, so anything you pull of there is a good (low V drop) feed to anywhere else,

My fuseblock has been melted in the past, and it's since been rewired and half the fuse-rail has been replaced with 9 little fuse-holders zip-tied together. Don't know if it was a home-job or if an auto-electrician did it, though I found a wire just poking out of the loom underneath the fuse-rail, turns out it's only live when the ignition is turned on. When I replaced my headunit a while ago, I noticed that the ignition wire to the stock headunit was dead. So I'm guessing this is why (cut at the fuseblock). Anyway, the same problem was still there... Stupid me didn't look at my volt-meter in the dash, I'm only getting a bit under 12volts max when floored. It seems to hover around 10volts when under no load at all, no headlights, nothing. When my headlights are switched on, the meter drops very low. I remember in my old VL SL the meter used to hover around 12volts normally. So I'm thinking my alternator is on its way out. I'll swap it over with my spare and see what happens. Thanks for your help man.

I wouldnt trust the voltmeter in the dash that much, its subject to years of vibration and dust can build up in it. It also takes its feed off some point on the circuit board on the back of the dash so it doesnt really get any sort of good reading, it far more often reads lower by 1 to 3v depending on load. The alternators, being slip ring types, suffer from buildup of brush material around the edges of the slip rings, the material is conductive and can bleed away some of the field current - although the regulator should compensate, it just cant feed more current into the field windings at revs under about 1000, The good thing is its quite easy to remove the alternator, take off the cover for the back where the brushes and regulator module is and clean it out with a soft old toothbrush... Regulators are pretty reliable for the most part though if you overheat your alternator it might blow one of the rectifier diodes, if that happens then it produces lots of pulses on the battery circuit, this can get coupled into the computer and make it a bit erratic - though if it gets to that level you would notice a whine on the radio that changes pitch when you rev the engine, Ive cleaned my old bosch alternator 3 times now in last 12 years when I noticed the battery volts low at just under 1000 rpms, its probably due it again though I am going for a ford transit alternator (100Amp) with shaft out the back so I can move my PS pump to that... You might want to consider tidying up your old fuserail for the unit I offer, since you have lots of odd fuses now jumpered etc, see link below