I have a ceiling light that I want to switch from two locations using 3-way switches.

Presently, a single pole light switch is within a box containing two other switches.

All white wires within this box are marretted.

Since there are only two wires to this existing single pole light switch, I have to assume that one is the feed, & the other comes from the light.

There is a black wire that is looped around the bottom or black terminal of the light switch. I noted that this wire also continues to attach to the other two switches in a similar manner.

Another black wire from a different source connects to the top or brass terminal of the light switch.

I have two 3-way switches.

I installed one of these switches running a 3-wire (red, white & black) between the switches, which incidentally, puts the light in between the switches.

I am having a problem figuring out how to hook up the other 3-way switch, which is replacing the original single pole switch

I have one wire too many.

There are the two blacks that went to the single pole switch.

Also, there is another black & a red from the other 3-way switch.

That makes a total of four wires, but I only have three terminals.

I marretted the white from the 3-wire with the other white wires in the box.