Thanks for the answers, but I'm not quite clear on some details. I
probably should have posted the oven and cooktop questions separately.
Let me try this again.

First, three clarifications:

A. In the cooktop junction box, one of the wires has red markings on
it, so there I can distinguish between red and black. In the oven
junction box, the two blacks look identical.

B. The cooktop clearly takes 240 volts. It is marked 240/120V.

C. I don't have a multimeter.


Questions:

OVEN

1. Is there any difference between the two black leads in the oven box?
Does it matter which one goes to the black oven wire and which goes to
the red oven wire?

COOKTOP

2. Does everyone agree I should just put a wire nut on the white-stripe
wire and not connect it to anything from the cooktop?

GROUNDS

3. In both junction boxes, the stranded aluminum ground is attached to
a lug screwed to the metal box. The oven ground wire is relatively thin
copper, and the cooktop ground is relatively thick copper. What is the
best way connect them to the box ground wire? Should I use Al/Cu wire
nuts on the part of the aluminum that extends past the lug?

MULTIMETER

4. If I go buy a multimeter, is it going to be obvious which wire is
neutral? How will I know?

CONNECTORS

5. I have seen expensive Al/Cu nuts from the Ideal company (about $5
for only two nuts). I think they have antioxidant inside. They look a
little small for my wire, though.

I also have some larger wire nuts and a tube of antioxidant. As I
understand it, the preferred practice when using wire nuts is to tape
them after twisting the wires together and embedding antioxidant in the
nut.

Another recommendation I have seen is to buy a special
aluminum-to-copper "bug" that has separate screws or clamps for the two
wires, and to tape it up after connecting the wires.

The old oven and cooktop had wire nuts with antioxidant in them. Which
is the preferred method?

--Bob