I am having a problem with the Sidekick.  There are two things that were worked on and now it won't start.  Unfortunately, it could be either one. 

I was wiring up some accessories last week and I checking the wires from the keyless entry / immobilizer circuit.  They were not working like expected them to and I stopped messing with it.  I am not sure if something I did while checking the wires caused a problem somewhere else.  How does the immobilizer work?  Does it send a signal to the PCM that must later be reset?  I did not try to start it last week after I was working on it.  I only had the one day at home and was mainly swapping things door panels and other cosmetic parts. 

I came back from a week out of town and decided to swap the transmission range sensor.  This was a possible cause for a 1875 trouble code that was preventing me getting the Sidekick inspected.  I did not try to start it, because I didn't want to get it hot.  I pulled the trans cooler hard lines, removed and replaced the transmission range sensor, and installed new flexible trans cooler lines.  When I tried to start it, the engine will not turn over.  I checked to make sure the range sensor was connected, checked the shift positions again, verified the reverse lights come on when it is in reverse, made sure it rolls when in neutral, and doesn't roll when in park.  I have tried to start it in park and neutral.  I also installed the old range sensor and it still would not start.  I am sure the I put everything back together.

Any ideas will be greatly appreciated.  I have to go back out of town tomorrow, but will keep working on it tonight.

As far as I'm aware, Suzuki never sold the Sidekick Sport with an immobilizer, so if yours has one, it's aftermarket, and how that works is going to be anybody's guess.

Find the starter control terminal - it's going to be a spade lug on the starter solenoid - and put a test meter on it, if you don't get +12V there when you turn the key to crank, start working your way back, I don't have the diagrams for the sport but the control signal typically goes from the ignition switch to the transmission NSS (neutral safety switch) to the starter - grab a meter and start tracing it.

The Sport diagram:

Please tell me where the starter motor and neutral safety switch are in that diagram...

It isn't in that diagram.  I believe that the P/N switch is part of the transmission range switch. The switch is shown in the lower right quarter of the drawing.  I installed the old switch again, to see if it was an issue with the new one and it still doesn't start.  I also moved the shifter through the motions while holding the key in the start position.  I can hear the fuel pump coming on bursts.  I can also hear a relay engage behind the center AC vents.

I will rig up a light to the starter solenoid and try that. 

I also moved the shifter through the motions while holding the key in the start position.  I can hear the fuel pump coming on bursts.  I can also hear a relay engage behind the center AC vents.

This would suggest that the ECU is receiving the start signal, which would in turn suggest that there is either a break in the wiring between the NSS and the starter solenoid, but after the splice that connects to the ECU, or the problem is completely unrelated to the work you were doing, and that the starter or starter solenoid has failed.

It could also be you pig tail ignition switch has worn out. Mod it by cutting the edge of the one screw hole and screw it back with washer to find more contact.

Bad connection at the starter.  Removed the wire, sprayed contact cleaner in it, brightened up the spade lug, tightened the connector slightly.

It starts now and no longer gives me the 1875 code after I turn it off and back on.  I was over complicating things.

Thank you everyone for your time.

Great that you sorted it out!

Yep, glad it was an easy fix```