What does the Ignition Housing Assembly have to do with starting the Engine? on 2008 Mazda Tribute

I've been having intermittent starting problems.I changed out ignition switch, coil antenna sensor and no change.had starter checked with meter it wasn't getting voltage. Took starter out and tested at shop it tested good.So We assumed no voltage is getting to starter from relay or sensor or switch.Battery good altI good.Locksmith said key lock and keys are good.Took it to dealer they said ignition housing assembly is bad.My question is what does this housing have to do with the Starting of the engine? Is there a main ground that is attached or power source that cranks engine? ?? I thought the Housing just holds switch key cylinder and sensor.I've never gotten into a wreak or never was ruff with steering wheel.I hope someone can explain this to me clearly.The housing comes with the says I don't need the other parts I can use same ones.Please any help would be appreciated.

Asked by for the 2008 Mazda Tribute
The housing portion is what TURNS the electrical portion of the IGNITION switch.
1 more answer
Before you go any further. Has anyone established that there is no power going to the starter S terminal when the key is in the crank position. Easy test, the small single connecter on the starter solenoid should get at least 10 volts when you turn the key to the crank position. If no you need a wiring diagram to back track the power. If yes then its a bad starter
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