2003 Gulf Stream with Equlizer Systems jacks question

Actually you want to wire them in parallel.
If wired in series, if the last switch in the line "opened" the other 3 switches could be active, but the signal would never make it to the panel.

In parallel, ANY negative output (jack down signal) would make it to the 1 terminal (pressure switch) on the panel giving you a warning.

Also, if changing anything like this I would advise making good notes, and packaging it into the space behind the panel so next owner will know what was done.