Car won't start after I replaced the starter and the neutral safety switch. What else would cause the car not to start?

Is it automatic or manual. If it's automatic try putting it in neutral and then starting it

other possible causes if battery and starter and starter solenoid been replaced.battery cables could be bad causing poor ground.if you have manual transmission could have faulty clutch pedal safety switch and automatic transmission could have faulty neutral safety switch.and could have fault in the theft security system.

Is the security light on or flashing ?
The yellow wire goes from the key switch to the neutral safety switch, then to the starter. So bypassing the neutral safety would make the starter crank the engine, but would have nothing to do with the rest of the engine.

check the adjustment on neutral safety switch, if it is off starter won't work, also check linkage for proper adjustment ,for the same reason.

It sounds like a fault in the starter circuit. It could be a defective neutral safety switch, starter solenoid, or possible a defective ignition switch but I doubt it. Can you hear the starter solenoid??? I'm willing to bet the problem is either with starter relay, neutral safety switch, or starter solenoid.

The neutral safety switch,or range sensor is mounted on the transmission at the shift linkage area.replacing it will require theshift lever to be removed

You need to replace and adjust your transmission range sensor switch. (also known as neutral safety switch) It is located under the air cleaner ducting on the top of the transmission under the lever where the shifter cable attaches.

It's most likely the neutral safety switch. Try putting the shifter in Neutral and slipping it just a little toward Park and see if it'll crank. If it does the neutral safety switch is the problem but worn linkage is the cause.
You've already check or replace everything else so it has to be this or the ignition switch.

The neutral safety switch is located on the side of the transmission and it is usually attached behind the shifter linkage and it is secured with two small bolts that can be loosened up to allow for adjustment of the neutral safety switch.

To adjust the neutral safety switch place the transmission into neutral, (block the tires) there is a notch or and indent marker on the housing of the neutral safety switch that should be lined up with a line on the face of the collar that is around the shifter detent shaft, and if they are not in alignment then loosen the two bolts that secure the neutral safety switch and then turn the neutral safety switch until they are aligned and then tighten the securing bolts to the neutral safety switch, and then test the starter. If the starter fails to engage then either the neutral safety switch is faulty, the neutral safety switch has been by-passed all this time and the by-pass (I will usually find things like a paper clip shoved into the vehicles wire connector with electrical tape around it) has fallen out of the wire connector from the vehicle wiring harness, or the battery just went dead. if you have the neutral safety switch from the old transmission still available try using it to test the neutral safety circuit. I have provided you with an image to help assist you adjust the neutral safety switch.

A number of items could cause this.

1 Worn shift linkage causing the neutral safety switch to not go into PARK or NEUTRAL.

2 Defective neutral safety switch

3 Cracked wire in the ignition switch, causing the anti theft system to prevent engine from starting

4 One or two bad commutator plates on the starter armature. If the starter stops so that the brushes land on the defective plate, the starter won't work. When it lands on a good one, it will. This requires replacement of the starter.

Long story short, you need a skilled mechanic to diagnosis this.

Charlie