Has anyone ever had this happen to them where they will be driving along at night and all of a sudden the headlights and dash lights seem super bright and then a few moments later they go back to normal?

One time it happened and my tach flickered off and back on.

Is that maybe a problem with a voltage regulator or the alternator?

 

Dead tach is Alternator, but I would check voltage engine running, then turn on everything and see what it reads

Cleaning the batt, grounds and adding more grounds from batt to engine and batt to rad support goes a long way

 

Had the same issue. It was the voltage regulator which sadly is part of the alternator. Catch it before the lights go the other way & the moments of brightness become moments of dimming.

 

yup, voltage regulator But you can buy it seperately on line and is not hard to replace

 

Couple other things to check:

1) Belt routing - Disco is the only vehicle I know where it's possible to route the belt incorrectly and it'll work ...but not be quite ENOUGH tension, to maintain charge, particularly at high speeds and at NIGHT with lights on!! If you drive around town a lot, you might not notice the problem at all, or for a long time. But at highway speeds and using accessories like the AC or lights on, it won't charge 'quite' eeenooouuughh. Difficult to diagnose if you measure voltage when the vehicle is at idle. Former owner or mech did it on mine and they chased electric problems all over the place for a long time till they sold it cheap ..and I finally figured it out, but not until after driving halfway across the USA, a bunch of goofing around when I got home and a thought by a very observative alternator shop owner who noticed glazing on the pulley. A few posts come up here now and then on it too. I almost did it last time I installed the belt. There is no belt routing sticker (on mine), nor in the owner's manual ... and the 'intuitive' path shall we say, is the WRONG way. So it's easy to do. What happens is the belt will eventually slip enough to wear the pulley ribs sharp, glaze the pulley/belt, and then when the output is reduced enough the dash gagues and lights will flicker all over the place like it's possessed by the devil herself (got to be a woman I fear). Ultimately the battery will go dead and you'll think the alternator is shot and replace it. If the replacer gets the belt routing 'right' the problem goes away and the problem was blamed on a faulty alternator. If the routing isn't correct at that point, the owner got screwed by the mechanic and after a bunch of return trips and hundreds of dollars later, owner gets frustrated and chalks it up to another 'example' of Land Rover bad quality problems (all from simple incorrect belt routing). I finally made a hand diagram which I taped to the owner's manual because I can never remember EXACTLY how it goes.

2) Check the pulley for sharp edges (should be somewhat flat tops on the ridges of the pulley grooves). Replace pulley and belt if that's the case. Don't use a cheap dayco belt.

3) Battery connections and down at the starter too.

4) Yeah, the alternators are easy to fix. Parts avail on the internet.

 

Verify this:

 

I forgot to post back up on this at the time, but I did get a voltage regulator off ebay and swapped it in for the old one on the alternator and it cured my dimming and tach problems.