okay guys, ive got a randomly flickering warning light, ive ignored it for a fair while now, but I guess its time to sort it out before I get stranded somewhere.
its popped up once before when my alternator wire broke, easy fix, and that's solid now so I doubt its that.
are there any problem areas where this could be affected? dodgy earths somewhere in engine bay maybe? potential watertraps? any help is appreciated
Which warning light is it? 300s don't have a generic warning light. If it is the (!) that is the brake fluid reservoir level sensor. I think the oil pressure warning light is an engine symbol. The battery light comes on when the voltage is low, if it is on whilst the engine is running the alternator is not charging.
Maybe there isn't enough vacuum from the engine if you're 'free-wheeling' down hill Aaaaggghhhh otherwise it'll be the leaky rubber seal in the servo casing?? Fluid level ;-? The brakes were always pretty sharp.
Doesn't make much sense, the light is for low fluid and would make sense if the cars attitude changes. Also possibly a bad contact. Pulling on the steering indicates uneven braking. So maybe 2 faults.
OK, so you go into neutral and 'free-wheel' for a bit so tick-over will be well-low. Then brake a few times and the brake warning light starts to come on and the brake pedal goes hard?? It sounds like its not getting enough vacuum from the inlet manifold due to tick-over being slow. Also, maybe the brake pedal is not returning to its correct height - I had that once due to the servo sticking. A temporary fix for that was to put my foot under the pedal after braking and pull it back. That was a different car though. Is the sender in the reservoir getting an air-bubble or something? Bulbs are ready to send up to you.
1988 340 1.4 GL, 218k, 5 door (Grey Bess). Gone to CBA. 1991 340 1.7 GL, 64k, 5 door, petrol blue (Deep Blue). 1988 360 2.0 GLE, 140k, 5 door, ocean blue metallic (Blue Bess). 1989 340 1.7 GL, 108k, 3 door (Red Ness). More info here!
A common problem is the vaccum pipe going to the servo, it can get soft and collapse under vaccum, or can go hard and leak at the joints, 1 way valve can go faulty but rare. Again nothing to do with the warning light, which would more likely be linked to a soft pedal, but the warning is a just a warning it doesn't mean the brakes will definately not work properly, so if the light is coming on check the level and if its OK, then the sensor is probably fault and not a brake fault.
A hard pedal is either a stuck caliper or lack of servo assistance. The 300 brakes are pretty good so braking should not be difficult.
Other problems can overheating or fading, where the pedal gets soft and the brakes don't work well. There are various causes, but the brakes are fundamentally limited in the amount of heat they can dissipate and withstand, everything needs to be the best for this to be minimised, new fluid , new disks pads etc
Indeed the vacuum assistance will go without the engine, however again I will say the warning light has nothing to do with this, it might be part of the self test when turning the ignition off/on but I don't remember how this works.
The brake warning light is a fluid level sensor only, there is no pressure sensor / switch.
I'll just qualify that by say 'for manuals', I'm not sure what goes on with autos.
The pre MY80 ones are quite shite 
