One EGT probe placed in the collector will measure the leanest (hottest) running cylinder. For a quick test of which one that is you can do the following:
With a running engine, take an EGT probe & touch it to the outside of each pipe. Make sure that you are measuring at the same distance from the header pipe flange or manifold runner. Write down the temperature of each pipe. This will tell you which cylinder is running hottest.
