Originally Posted by Johnny Monsoon
Obviously, what you have failed to do is read the post at all.
The needle never came off the instrument at all; the dash instruments never came apart, just the dash cluster was removed from the dashboard, intact.
The problem is an electronic one. There's a sender at the tank that tells the needle what it should be indicating. There's a capacitive circuit at the needle itself (in the dash cluster) to retain the last state information. When I de-coupled the instrument cluster, I had to remove the sender input from the gas gauge. When that happened, the needle remembered where it was at the last fill. So, there sat the actual gauge, doing a good job as it was supposed to at reading 1/4 tank full. When I reconnected the dash pod the tank sender told the needle that it had a quarter of a tank of gas. So, the needle responded accordingly and moved the needle up a quarter of a tank higher than it had been sitting. Thus, my gauge reads 1/4 higher than it should.
i have actually replaced the sending unit on my 96 and am quite familiar with the circut using a capacitor and a resistor to slow the movement of the needle so that it does not react to the constant movement of fuel in the tank. i am not aware that the capicator maintains its voltage because the resistance of the meter (needle) would drain voltage from the cap over time, i suspect the needle has no return spring therefore mechanically it stays at the same reading and has no connection to the cap while the ignition is off, i am unaware of any meter that draws 0 current out of a cap to maintain its position and i am aware of no capicator that doesnt have a small amount of leakage either. so i am not 100% sure of your theroy, not saying its not possible however.
that said and considering the circuit is nothing more than a simple series circut with the sending unit, the resistor and the cap that changes voltage across the cap and the cap likely drains or looses voltage through the meter circut as a high value resistive load.
i suspect that in newer tacoma they use a stepper motor, so the circut that drives the motor knows wether to step it forward or backward depending on voltage. this means it does not have a reference point to count steps from. that said, if you either move the needle without removing from the shaft or remove the needle and reinstall it in a new position does exactly the same thing. i think in your case you need to fill the tank drive home and with the ignition off move the pointer to the full position. if it is a stepper motor it should reference the new position, if not then i would suspect you have in some way altered the voltage reading to the meter itself.
i do know that with my sending unit the potentiometer on the sending unit in the tank goes to ground. if memory serves me it should be reading 12 volts on the sending wire with a full tank. you could probably trace the circut in the cluster across the cap and read the same 12 volts across the cap. that will tell you if your getting the signal your supposed to. you could install a POT on the same sending unit wire to ground and vary the resistance to verify the operation of the gauge when you think you have the problem sorted out. this way you dont need to drive around thinking you have a full tank for 50 miles before you see any movement.
from what your telling me i think your theroy is correct, somehow it remembers the position (im guessing its a stepper motor) and untill you removed the power it knew how many steps from empty it was, so it advanced the needle the same number of steps based on its initial reading.
i think you can get there in 1 of 2 ways, either remove the cluster as you did previously and set the needle at just below the empty mark. or without removing the wireharness from the cluster put the needle in the full position with a full tank. i would use a full tank in either case because its a lot easier and logical to test its position knowing its totally full verses finding empty the hard way.
i think if you have to disconnect the wire harness again from the gauges on a full tank and setting the needle at below empty as most cars are as long as the needle returns to just above full on a full tank your good to go. if not you have to repeat the process moving the needle to back to empty in a new spot to get it to go to the expected full position. i suspect it will move the same number of steps from where you started each time you connect and power it up.
also FYI the low fuel light uses a thermistor, it gets warm when the fuel is low because there is no gas touching it to keep it cool, as it gets warm due to its own internal resistance it drops in resistance value, it essentially goes into thermal runaway creating its own heat. this turns the light on via a voltage regulator so that when the light comes on its full brightness verses on the older trucks and cars will glow as it heats up and resistance lowers and voltage increases across the internal load resistor.
and yea i have a pretty good background in electronics too