Wiring problem?

[classicgm]

The fuse box rotted out in my poor Jimmy so I pulled a harness from a truck at the local j/y. Unfortunately there is a difference between the two (two heavy gage purple wires on the steering column) but I have a ride with friends today so I went ahead and put it in to see how my luck goes.

Everything has gone well EXCEPT for I have no taillights or turn signals. Bummer! I've checked the fuses and connections but I haven't anything yet. I'm hoping that it's in the headlight switch because it is REALLY crusty. The dimmer coil is unsprung, the shaft sticks, etc. I'm off to the parts house to pick one up but could it be that the wiring harness is incompatible?

My truck rides on 42' swampers so I hate to tempt the law riding without any taillights.