I don't know if a pathfinder is the same, but in my Jeep the transmission has to be in neutral before it will go into, or out of, 4 low
2 wheel low 4 wheel low Neutral 4 wheel high 2 wheel high
You have to be stopped with the transmission in neutral when you shift in or out of low 4 wheel drive. Park doesn't work as neutral. When you push the rocker switch up for high 4 wheel drive once you will be in high 4 wheel drive, push it again for high 2 wheel drive, you can shift between high 2 and 4 wheel drive while you are driving.
The 4 wheel drive light will do this most often if you try to switch into 4wheel low at a high speed, usually over 35 MPH. 4 wheel low is made mainly for when you are stuck and or when in mud or snow. If the question was for 4 wheel high. Stop the car press the button and it should stay on without blinking. If you suspect that it is not going into 4 wheel high or low. The valve unit that engages the gear may be the problem. Front underside of the transmission, has wires coming out of it.
If it has 4-wheel drive you would see controls on the dash to engage 2-wheel high, 4-wheel high or 4-wheel low.
The drive switch to the lower right of the steering wheel has 3 positions: Left to right they are A4WD, H4WD and L4WD. When the switch is in the H4WD position, you are in High 4 Wheel Drive.
check the 4 whell high actuator
Theres a switch next to the radio on the left side, it says 2wd High, 4wd High, 4wd Low and Auto, put it on 2wd High or it might just say "2H" just 2 wheel drive
I believe you have a 2 high, 4 high and 4 low. There is no 2 low.
4 gears over 4 gears with a switch to switch between low and high 1234 then 5678
There is a lever on the tranny hump between the front seats ... pull it back into 4 high then push it down towards the floor to pull it back into Neutral or 4 low. Reverse this procedure to return to 2 high.
If you have push button type, just push the button. If you have a selector switch , turn switch to desired setting. If you have a floor lever, pull, or push to desired range. All have to have transmission in neutral to shift down into low range. High range can be used without any changes. You may shift in and out of 4 x4 high and 2 wheel drive while moving. Just let off the fuel pedal to match wheel speeds and shift from 4 x4 high to 2 wheel drive, or back.
The lever you are talking about is the four wheel drive selector and for normal driving it needs to be in 2 wheel high which is farthest forward each stop from there is 2 wheel low, neutral, 4 wheel high, and 4 wheel low. As far as overdrive is concerned if its even an option on a 79 would be built into the automatic transmission with no on or off switch.