1991 ford tempo auto trans will not go foreward nor reverse

check the trans fluid ?can you here the van go into gear or not at all ?

You add trans fluid through the trans dipstick tube (NOT the engine oil dipstick). Check your owners manual for the proper method to test the level, most cars lately you check the level with the trans fully warm, in Park, engine running, parked on a level surface. (Set the parking brake, block the wheels.) You will need a long funnel, available at any auto parts store. Do NOT overfill the transmission, as this will cause damage to it.
Use the correct type of trans fluid, check your owners manual.

The shift linkage could be wearing out inside the transmission.

Sounds like a bad alternator. Most auto part stores will check these for free. All you have to do is get it off the van (which I know is no easy feat)

turn every thing on in park if voltage drops change alt

It would take way to long to tell you a step by step procedure in here.
You can get a haynes auto repair manual for that car, it gives a step by step procedure on most major removal and installation jobs. Most auto parts stores stock them, about $17.00.

If I understand you correctly? You may have a plugged filter. Try servicing the trans. EG: Trans filter kit and good quality fluid that meets or exceeds Ford specs.

it cant shift on its own.i think that you assidentally did it yourself.

The dipstick is near the master cylinder behind the throttle body.

It's right next to the air filter and behind the radiator fan and to the right of the oil dipstick. The transmissions is black and the oils is yellow. If it's a manual, there's no dipstick there. If not check close to the forewall towards the back of the engine.