ooh the 98 doesnt have hazards (yep i did a quick look on ebay to double check)
if you get a later model switch with the button and have a look through the two wiring diagrams to find the difference you should be able to fit them easy enough with an extra couple of wires

my carb heater hoses were blocked to buggery but as i was messing with the carbs all the time i just bypassed it, if you keep your bike in a garage then it isnt an issue and when it is really cold it isnt either as i was ridng in ice and snow the other month that didnt cause any issues (and im riding with pods which would make it worse)

just sent you a pm

https://www.ebay.co.uk/itm/yamaha-fazer-fzs600-1998-water-pipe-journal/232258174221?hash=item3613aa7d0d:g:HKUAAOSwTM5YuDED

it could be a weak mixture so the corrosion inhibiters are not strong enough yes
a catalyst to corrosion could also be caused by limescale which is caused by hard water in hot systems


-- from a central heating company --
The building blocks of limescale are calcium and magnesium.  Thus, one would think that limescale should have a white color.  Yet, limescale deposits are usually brown!  When limescale deposits build up, iron and oxidized iron particles get caught and are imbedded in the limescale.  Rust firmly attaches itself to your pipes, causing serious threats such as corrosion.

if you go track racing (road racing) you have to use water only - no coolant is allowed following acu regulations
water is one of the best coolants there is but unfortunatly for us it freezes and in some areas is full of crap
hard water areas should not fill coolant straight from tap thats one of the things that causes issues

any chance of a pic of the crud
the yellow bit has me confused
is it bitty or sludge like ?

certainly sounds like a balancing or idle fuel screw area to be looking at
as davie says start with balancing as idle fuel screws dont tend to change as much

just had a thought as we here about flashing and we think instantly of indicator speed - you havent by any chance got one or more of those silly fuses with the led to tell you its broken in do you
i did once upon a time and this happened
https://youtu.be/qQ3LK1O4vHM?t=3m57s

waited for postman, drank beer, then tried to fit rear wheel bearings only to run out of blowtorch gas so couldn't sweat them all in so started on my brakes to realise there is 18 yrs of crap fouling everything up and forcing one pad into the disc all the time so decided to throw in the towel and drink more beer
(banana bread beer is as weird as it sounds but somewhat nice)
tomorrow it will be calipers in the oven so i can hopefully remove the joining bolts then give them a bloody good clean out and wait for the new piston seals
by mot time that will have the newest back end in the country lol


on a plus side i did get the sprocket carrier bearing in so its at least one step in the right direction

not seen this happen before but to start i would clean the contacts going into the relay - will do a bit of digging later on when i can and see what i can find
(im assuming it is in neutral when it is flashing and not flashing when in gear)

i couldnt find it for the life of me lol
be a bit off now as i have just found why my rear pads are wearing unevenly and have to pull my callipers apart and blast them clear of crap to hold the retaining clip in correctly instead of the dodgy angle it has been sitting at
and of course the bolts are stuck solid so up early in morning to throw the calipers in the oven while no one is in the house (windows wide open)

and that is just porn im assuming adjustable aswell
think i might just save that pic to my folder of goodies