'05 Mercury Mountaineer - No voltage to starter relay. Brand new starter. Brand new neutral safety switch. Won't start in park or neutral. Get a reverse light when shifted there. Have 10.55 vdc going to the ignition relay. Fuses are good.

85 & 86 are the control side of the relay , one should have battery voltage (85) the other (86) doesn't .86 is control from the PCM - engine computer . PCM supplys a ground to close contacts inside the relay sending battery voltage to the S terminal on the starter solenoid . If the PCM doesn't see a voltage signal fron the park neutral safety switch it won't energize the relay .
Circuit Description (ECM/PCM Controlled)
Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM)/powertrain control module (PCM) Crank Request circuit. The ECM/PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the ECM/PCM receives an engine run flag.

Do the headlamps work ? Are they bright ? Turn the key to start position ,do the headflamps dim ? I am assuming that when you turn the key to the start position nothing happens ! Starter doesn't spin . What engine size ? 4.0 or 4.6 L ?????
Do you know how to do automotive electrical system testing ? How to use a wiring diagram to find point's in the circuit to test from . When you turn the key to the start position a B+ voltage signal is sent to the PCM - engine computer , to signify that start is requested > If there are no problems with the anti-theft system the PCM will supply a ground to the starter relay . Has to have B+ voltage supply from fuse F2.29 10 amp in the central junction box . Voltage from this fuse goes to the park neutral safety switch an through to the starter relay if the park safety switch is good . Then there is the load or starter side of the relay , If the switch an relay are good an the pcm energizes the relay B+ voltage from fuse F1.12 a 50amp fuse goes to the S terminal on the starter solenoid .

http://www.bbbind.com/free_tsb.html free wiring diagram ! Enter your vehicle info. year , make , model an engine size ! Under system click on engine ,then under subsystem click on starting .Click the search button , then on the link ! View what all is involved in the starter circuit of your vehicle . Look on youtube for how a relay works . Watch some videos on basic electrical testing .

Battery good , cables and connections ? Voltage drop test starting circuit . Find a wiring diagram at http://www.bbbind.com/free_tsb.html Your vehicle has no relay ! Try wiggling the gear selector from park to neutral . Check B+ voltage at the park neutral safety switch . When you turn key to start B+ voltage goes to the neutral safety switch , if switch is good ,B+ voltage goes through the switch if in park or neutral to the solenoid on the starter . IF all is good starter energizes and spins the engine over . Starter Voltage Drop If you can't fix it with this info , your best bet have it towed to a qualified repair shop .

Safety switch ? For what ? Park neutral safety switch ,is this what you mean ? Your vehicle not starting ? There is a lot more involved then just that switch.
Circuit Description
For ignition switch power modes refer to Body Control System Description and Operation. Once the ignition is placed in the Run/Crank position, the control circuit of the Run/Crank relay is grounded by the body control module (BCM). With the Run/Crank relay switch closed, battery positive voltage flows through it and on to the park/neutral position (PNP) switch. With the PNP switch in either the Park or Neutral position, battery positive voltage will flow to the starter relay coil supply voltage input terminal of the powertrain control module and the coil side of the starter relay. Placing the ignition in the START position sends a message to the engine control module (ECM)/powertrain control module (PCM) requesting engine start. If the ECM/PCM has determined that the transmission is in Park or Neutral and theft is not active, it will ground the control circuit of the starter relay. Battery positive voltage will then flow through the switch side of the starter relay to the S terminal of the starter solenoid, cranking the engine. For remote vehicle start (RVS) information, refer to Keyless Entry System Description and Operation.

Could be neutral safety. You can unplug the connector and use a jumper wire to test it. Could also be igniton switch,but neutral safety is more common failure and cheaper and easier to replace.

Starter solenoid or neutral safety switch or bad key switch or broken wire or bad connection.

Park neutral safety switch maybe be the reason for the no crank ! Try putting the vehicle in park ,then try to crank the engine . Testing the electrical circuit is the best way to trouble shoot this problem , along with do a voltage drop test on the starter circuit ! This will test the battery cables an connections .
Starter Voltage Drop
How to voltage drop test starter motor circuit
Does it have a manual or automatic transmission ? Manual ? clutch switch . Looking at a wiring diagram I also see a starter cut relay !
http://www.bbbind.com/free_tsb.html Free wiring diagrams . Enter vehicle info. year , make , model and engine size . Under system click engine , under subsystem click starting . Then click the search button , then click the blue link ! Check the starter cut relay also . Videos on youtube showing how to test a relay controlled circuit !

when it won't crank you will need to start at the battery and work your way to the starter checking for voltage
battery - cables - ignition switch - neutral safety switch - starter

So what it only does it in park or neutral ! The vehicle starting circuit is only suppose to let it start in park or neutal . Park neutral safety switch won't allow B+ voltage to S terminal on the starter solenoid unless the vehicle is in park or neutral . It's probably the starter relay contacts stuck closed . You really should learn how it works before guessing as to the problem . Plus learn automotive electrical testing ! The ignition switch when turned to the start position send's a voltage signal to the PCM - engine computer .The PCM will energize the starter relay to crank the engine . PCM / ABS 10amp fuse in the I/P fuse box supply's B+ voltage to the park / neutral safety switch . When in park or neutral the B+ voltage goes through the control side of the relay to the PCM which will supply a ground to energize the starter relay .

starters are simple, big cable supplies direct power from battery. little wire gets power from starter relay after ignition switch is turned to on position. relay is located under hood in relay box on left fender.car safety neutral switch also has to be aligned and good try starting in neutral.