Help needed...

Hi,

I have a 90 Mustang 2.3 LX on 14.000 original miles.
This car was sleeping in the garage about 5 months
Last weekend,I took it and got out to cruise a bit.
I checked everything,put extra water,oil etc.everything was working like a clock.
All of a sudden,the transmission (automatic) started to go crazy,
On 'D' when car stops or slows down, it was removing the gear,after a couple of little steps on the gas,it was catching the gear again.
I didn't take it really serious that day,but last night,I was out again.
On the way home, it started to do it in like everytime I move my step off the gas,on 'D' it was acting like it's on 'N'.
Quarter mile away from my garage,it started no moving anymore.The gears was not giving any reactions and the engine was running like it's on 'P' or 'N'.
So I pushed it to garage and slept.Now I got near the car and checked transmission oil.The answer of the stick to me like I was waiting.
It was a big EMPTY.Nothing in it.(My stupidness)
I took the oil from the trunk and was gonna put transmission oil,came to the engine.And I could NOT find the transmission oil cap anywhere!
Because I have never put tranny oil to the car before.
Now my question is, where is that oil cap so I can put some tranny oil?
Or,could it be something else but oil?
Thanks for your help.
 
You add transmission fluid via the dipstick tube.

Take the dipstick out first, obviously. Its best done by putting a funnel in the top of the tube, and pouring fluid in. Can be a pita.

Note that you are supposed to check the trans fluid witht the engine running, and in park.

Check the owners manual, to be sure, but you should have an A4LD auto trans, and it should take Dexron 3 fluid.