Pull Up/Down Switch Video

Hello-

The other day, my internet decided to cooperate and I watched a video where Paul was doing what I think was Circuit Integrity involving a Subaru door locks and also using a test light to identify a Pull Up or Pull Down type switch. It was very informative and I took some notes as I was watching. The thing Im still a little confused on is exactly what a Pull Up or Pull Down switch is? Meaning, does the switch get is power from 2 different sources and do the words "Pull Up and Pull Down" relate to the change in voltage while using the test light. Any clarification would be great-

Thanks-
Mr Mike

A pull down circuit provides a ground when activated good examples are fuel injectors which are supplied with battery power when the key is on but the engine computer controls each injector by switch the ground on and off.
3 wire cam Hall Effect Cam sensors usually work by pulling the voltage on the signal wire down.
Another example would be the brake pad wear LED indicator on many BMW in normal conditions the circuit forms an continuous path to ground from the instrument cluster to ground and the LED warning lamp is out. When the brake pad wear sensors are worn through the path to ground is broken the terminal is no longer grounded and the the light comes on.

A lot of circuits on modern cars are controlled this way even simple things like the screenwash or the horn. The horn beeps when the body control computer module provides a ground.

Pull up circuits are controlled or switched by switching

Thanks Andy-

This seems to clarify a bit more for me with the understanding of how they operate. I really appreciate it. Maybe you can help with an issue I have with my truck. Here is the run down-

2010 Dodge Ram 1500 (5.7) HEMI

A few months back, I was having intermittent starting issues- meaning that sometimes the truck would start right up and other times, I would have to keep the key turned to run/start for anywhere between 15-45 seconds before it would start? I checked the Batt(+) cable going to starter and was getting proper available voltage to the starter. Also verified the Batt terminals/clamps were clean like newborns baby butt. When it would start and Id drive a small distance and turn the truck off, it would not start again, but would if I hooked up jumper cables? I checked Batt volts and was reading around 12.6V. I was getting the "Red Lightning Bolt" on the dash, so I hooked up my scanner (Autel MaxiSys) and got a code P0123 or bad throttle body. I researched this before I even new Scanner Danner existed and everything says to replace the throttle body. I replaced the throttle body (I know) and same thing. Then people say its the WIN (wireless ignition node) which is not wireless because it has a small 12 pin connector on back with just 8 wires. I took off the WIN ignition key box and opened it up- the small contact arms looked good, so I went ahead a got a q-tip with rubbing alcohol to clean what I could just to be on the safe side- still no difference. Out of curiosity one day, I got under the truck and had the wife turn key to run- No power at starter solenoid? I Ohm'd out the Yellow/Grey wire from starter relay- it was good. I also bench tested the relay with a 9V battery- it was fine-(clicking). I have since torn apart the dash and cleaned up any grounds I could find to include engine and chassis grounds. My next step is to check the starter relay sockets in the TIPM to see if they check out. Also, if Im not getting the volts to the starter solenoid, Im thinking it could be the Neutral/Safety switch which Dodge calls the Transmission Range Selector which I have not tested yet. I dont want to assume anything because I did push ups years ago in the military for using that word.

Im somewhat stumped but am convinced it is probably something very simple. I have the complete wiring diagram from Mitchell and also a downloaded "Shop Manual" supposedly the dealerships use. The shop manual stated that after replacing a throttle body, use a scan tool to do a TPS/Throttle Body Re-learn but my Autel scanner does not have this function.

I need some guidance on this please. Any info/recommendations you could give would be greatly appreciated.

Thank You Sir, in advance-
MrMike