One trick you can use to help the troubleshooting is to connect a 12V test light in place of the fuse. As long as there is a short circuit (or very heavy current draw) the light will glow, and once you have isolated the short the light will go out. This does two things... it allows you the luxury of working on it while the circuit is energized, and it gives you a visual indication of when you've found the problem.

Most short circuits happen at connectors that are subject to motion, heat, or corrosion. I'd say lamp sockets are a prime candidate, but if it's only the turn signals on the circuit, the fuse shouldn't blow until the turn signals are activated. If the auxiliary coolant pump (for the heater) is on that circuit, that could be a problem also.

Good luck!

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1987 W201 190D