Hey I've just pulled out my instrument cluster on my 1988 740 and on the back in the right bottom corner, there are two numbers 601 with a lock symbol and 801 with an unlock symbol, i'm assuming in that little gap is a switch. what is it for???

Thanks

Steven

Steve,
The thing you are looking at is a "jumper" for the fuel gauge to give correct readings on a car with 60 or 80 litre fuel tank capacity.
The 601 is actually 60l (lower case L) if you look carefully. The "padlock symbol is showing you the jumper fitted for 60 litres, removed for 80.
Glad I`m not the only one to be confused, it took me a while to figure it out!
Colin.

Ok in that case, how do I remove the jumper, because I think my gauge is marking incorrectly because I occasionaly manage to get at 50 or more litres of fuel in while the gauge is still marking just over the red. I'm thinking I do have an 80lt tank. What tanks did they fit on which models???

If you have the jumper in place you can see it. It is just a "u" shaped bare wire (just like the opening part of the padlock) pushed through the two holes in the back of the cluster near the "padlock" symbol.
Not sure which models had the larger tank capacity but the UK Haynes manuals mention an optional aux. tank with it`s own sender unit, for the wagon models, I think. Also there is a longer tank sender unit/in-tank pump unit listed for later turbo models which implies a bigger single tank.
No doubt someone with more info on model specs will tell us the details.
Don`t place too much faith in fuel gauge readings as they are not exactly precision devices at best, and wildly innacurate at worst!
Colin.