DIEGO1951

I need some help please. I am using 5 Peco side mounted turnout motors on my track. I have successfully wired up 4 of them using terminal blocks to 4 Peco passing contact changeovers in the Peco switch module unit (PL50). I am using the Gaugemaster CDU unit. However the fifth one is proving a nightmare. Without the electricity switched on , when I connect the black wire into the module unit, I get a slight electric crackling noise and when the green and red are connected and the electricity then switched on, nothing works nor do the other 4. Why does it make that noise if the electricity is not switched on? When that 5th one is disconnected, all the other 4 work ok. I am a total novice re electrics so not sure what the problem is. Is it a defective point motor? Is it the 5th switch module extension (PL5) which is faulty? Hope someone can help?