I had noticed that once I had the ALU connected to other parts of IO, that the logic levels were not all high enough to light up the led's. The big problem was when all four A inputs ( or B ) were set high and then set the first B ( or A ) input high then the only output should have been just the final 16 carry bit. However this was not the case and when I measured the voltage I found the high logic was down to about 2 volts. Way too low. I decided to insert a non inverting buffer between the third bit carry out and the fourth bit carry in. This raised the carry logic high level back to near rail voltage and all combinations of adder/ALU inputs produces the expected outputs. I had to create a cardboard support platform for the added circuit.