Hi Joel,
by googling around I found out that your MRC 1400 power pack has a power output of about 14 VA. (VA or Watt is the physical unit for measuring power. You get the power by multiplying Volt times Ampere)
This means, that with an output voltage of 12 Volts (normal for H0) you can only draw a bit more current than 1 Ampere. If you run 3 locos and every one of them draws only a current of 0.5 Ampere, you already have an overload: 1.5 Ampere x 12 Volt = 18 VA!
) The transformer overheats - and pop goes the circuit protector...
And if you add additional loads at the AC terminal (signal lamps, turnout motors...) it gets even worse. :curse:
Such is physics - you simply can't get more power out of of a transformer than it is designed for. Therefore there is no such thing like an Amp booster!
To get more power from your pack, you had to rewind the whole transformer. BUT: Hands off from such an enterprise! This could be VERY dangerous - you don't want to be electrocuted, would you?
Sorry to say, but it looks like your power pack was simply not powerful enough to run your whole layout. So most probably you'll have to swallow the bitter pill and hunt for a more powerful pack. I'd recommend something with a 30 to 50 Watt power rating. In the long run you are better off when you pay a bit more, but then you have ample power to run all your lokeys! :thumb:
Ron