could someone tell me why a 1985 el camino 305 engine has two oil sensors, one right behind the intake manifold and the other right above the oil filter. which one does what.

My 85 only had one by the oil filter someone must have added that by the Dist? Thats where i moved mine to clear the Headers :texas:

The oil pressure switch by the distributor is used for controlling the electric choke lead on the carburetor.

On my 84 Elly with a 305 the two are: oil pressure switch located back of engine near dist. and oil pressure sender located above oil filter.

I have not run across 2 senders before, but it doesn't mean that they aren't out there. The sender for a vehicle with gauges will only have one terminal and is sort of "fat". It will vary resistance with the output of the oil pressure and thus control the gauge inside the car. The "idiot light" sender will have 2 terminals and all it just opens or closes a circuit to light the oil pressure lamp inside the car. The threshold on it can be as low as 6 psi or so. The carb choke is wired in with the oil pressure switch so that if you sit in your car with the key on and not running, your carb choke won't warm up and open the choke plate. Then when you start the car....no choke effect even though the engine is cold. With oil pressure it closes the circuit to the choke and only then will it warm up the choke and start opening the plate. As to why you have 2 senders......in the words of Herman's Hermits "why do the birds go on singing....why does the sea rush to shore...." He didn't know either.
Craig (windchill of -40 degrees...in New Mexico....this ain't right)

Don't know about Herman's Hermits doing the song, I know Skeeter Davis sang it too.
As for 2 oil pressure switches, search "Choke Light" for additional explanations.

2 oil sending units : one at rear of intake manifold as stated before. The second low one on the drivers side of block is for a mech. gague in your dash gage cluster. What trim level does your truck have ?

1985 choo choo ss

Then the answer is 2. The lower one is for the dash gague...