If you are lucky (and no one has messed with it) its written on the cap.
If not remove cap, remove #1 spark plug.
Hold thumb over spark plug hole and have a Friend "bump" the engine over about a 1/4 turn per time. (or use a remote button)
The air will puff out when the cylinder is coming up to top dead centre.
Then carefully turn the engine until the timing marks are close to lined up.
The ignition rotor will now be pointed where # 1 is. Mark and replace cap.
Number 1 plug position will be listed on the cap. Now if you know the firing order, and you know the direction the distributor is turning, you then will know plug positions as connected to the distributor cap.
The marked # 1 position on the distributor cap faces towards the REAR
Number 1 on the distributor cap is the top post closet to the firewall. Looking at the distributor cap it would be... top row 1-3 bottom 2-4
where is number one on a vortex 4.3 v-6 distributor cap
The cap should have a #1 mark.The cap should have a #1 mark.
Front righthand side of cap
The distributor cap should have the number 1 marked on it. The distributor cap is installed with the # 1 position facing the engine , slightly towards the drivers side of the engine
Should have a small number 1 on the top of the cap.
# 1 on the distributor cap faces to the FRONT / CENTER
# 1 on the distributor cap faces to the FRONT / CENTER
The marked # 1 position on the distributor cap faces to the FRONT
in number 1