i have a marshall 1960 cab and when i plug it in the 4 ohm jack on mono it only comes out of 2 speakers but when i plud it in the 16 ohm jack it comes out of all 4. could there be a problem with the 4 ohm jack? ive opened it up and checked all the cables. everything looks fine. any suggestions?

P.S. if anyone has this cab mind taking a picture of the inside of the jacks? i just want to check to see if the cables are connected right.
My Rig:
ESP LTD EX-400BD (two of them)
Peavey 5150
Mesa 4x12 Straightback Slant cab loaded with v30's
switch it to four ohms? im gettign this cab in a few weeks. is it good? what head do you use?
your impendance might not be correct on your amp. not sure.
Use it on 8 ohms, surely your amp outputs in 8 ohms if it ouptuts in 4 and 16??
My Gear:
Jackson RR3 + Bill Lawrence L500XL

Sennheiser EW500 Wireless
T-bone EWS wireless
MXR 6Band EQ
Ibanez WD7

Peavey VK100
Epiphone ValveJunior
Kustom Quad100DFX 2x12
Marshall 1960A 4 x 12