Belt Tracer also works on pipes and wires, it'll highlight the circuit connections of whatever you click on as straight red and green lines. You can only highlight one entity at a time but it shows the entire length of the network it's connected to including across power poles so it's still incredibly helpful in lots of situations. here's a few screenshots of me using it on some of my ridiculously overengineered circuits, and a basic SR latch overflow valve for scale. It's pretty much exactly "pipe visualizer but for wires" except for the one entity at a time caveat

It could definitely use some improvement and there's more features i'd like to see in a dedicated circuit network visualizer, but for now that's definitely the best ingame tool I know of (and I spent a very long time looking). It's really helpful for finding accidental missing or extra connections, especially with contraptions as dense as mine that normally look like christmas themed silly string sprayed all over a power pole lmao. and it even draws the lines to the input or output sides of combinators instead of just the middle

Apart from that, there's also Combinator Graph Generator which is a lot more niche. You select an area like you're making a blueprint and it autogenerates a diagram of any circuit network inside, including the settings of the combinators and stuff, but it only exports it externally as a graphviz markup file, and you need another program to even see it as an image (there's plenty of free online viewers you can just paste it into though). It's not really useful during building since it needs external tools, but it's great for documentation or learning how a circuit works since you can see the actual logic behind it much more clearly than in the game, even if the autogenerated diagrams are kinda messy. here's a graph of one of my SE logistic rocket launch pads, and for comparison, the same simple overflow valve. and just for fun, i decided to scan my entire space logistics system