Hi as of title really, the first few weeks I was riding the k100 it was fine however as of recently the fuel lights seem to only come on at random intervals. Now I'm not sure where to start with this problem, I thought it was an earthing problem after the starter motor incident however that hasn't sorted it out. So far I'm just using the trip and fill up every 100 so miles (taking £15); doesn't bother me doing this but I would rather sort the niggle out. Which shouldn't be that low MPG really should it

I was also thinking it could be the bulbs however as I've recently checked it happened in london when I was doing a courier job that the 4 litres light came on and was working. Then both the 7 and 4 litres lights came on. Managed an extra 30 miles out of it and still had about 5 litres left in the tank at the end of it.

Just wondering with all your intelligence any idea what it could be, possibly fuel sensor

Oh here is a photo from one of my last rides it's not the best but I quite like it, I'm getting the panel painted and have a tinted screen on order. From another thread couldn't afford the comfort seat on my last trip so unfortunately never got it. Going to be looking out for another and a red top box if anyone has one knocking around.

More than likely it will be the sensor itself. Two thermistors are used one for 4lt and one for 7lt. they proved to be unreliable in 1983 so were abandoned in favor of the more conventional float set up of the later type.  I don't know of anyone who has successfully repaired them but I would replace the tank with the later model even though there is a fair bit of work doing it or just continue on as you are

It MIGHT be a connector issue. Pull the left lower fairing and try jostling that a bit to see if that helps.

If it does turn out to be a connector issue then there's a "free" replacement on the bike already.  The unused white 4 lead alarm connector in the relay box is the same.

As Rick noted, putting on a newer tank is feasible but requires some modding/fabrication since the rear mounts to the frame differently. And then there's painting unless you find an identical/acceptable color.

Simplest solution: Reset the trip odo every time you fill up and keep an eye one the miles/kms to know when to fill up again.

Unfortunately, been there done that......reset your trip meter as suggested or get yourself another trip meter/speedo by buying a push bike trip computer...fairly cheap and you have another trip meter to use. ( Sigma brand). The only way of fixing the problem is to buy another sender unit..which will end up the same way as your current one.