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I have a bathroom switch that contains 4 sets of wires. From L to R it's: Exhaust fan, Power in, Hall lights, Bathroom light. I tried installing a dimmer just to control the bathroom light, but because there's only one hot in, I can't figure out how to control the light with a dimmer without controlling everything else with it. Either I join all the fixtures with the hot, or there's no way to give power to the fan and hall.

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    Did the switch that was in there control everything before you started?
    – JPhi1618
    Jan 13 '20 at 22:59
  • I see 5 total cables (one on the lower right) and 3 black wires loosy goosy. How was it wired before? Jan 13 '20 at 23:45
  • No, the switch only controlled the light. The lower right wire was just...there. I did, however, figure it out. I had reversed the wires on the dimmer so that it became the first in the serial instead of the last. I made the switch and ended up having to combine all the elements to the hot wire, which made me nervous but seems to work just fine.
    – Alimun
    Jan 13 '20 at 23:58
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    Trimming the wire was probably a mistake, you really shouldn't do that (in case you need it one day). I see a HOT wire in the back-middle that looks to be flat as a pancake (or an optical illusion). A bunch of those wires look to be bent to promote kinks and binds which is a bad approach to wiring a box up; this stresses the wires and promotes future troubles. There's also grounds not hooked up? They should be (appears to be in middle conductor for one).
    – noybman
    Jan 14 '20 at 3:42
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    This was already after I opened everything up, so I reground it before I closed it. I didn't trim the wire all the way back, just the copper down to the insulator for a little protection.
    – Alimun
    Jan 15 '20 at 1:02
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How about we start by marking some wires with colored tape.

  • Wires that are supposed to be hot all the time get marked black.
  • Wires associated with the fan hot (that we switch) get red.
  • Wires associated with the lamp hot (that is dimmed) get blue.

Mark the appropriate hot wires amongst those five cables.

On the dimmer, you mark the supply wire black (is probably already that way) and mark the load wire blue (since it goes to the lamp) (it might supply as red, but we mustn't connect it to the fan!)

On the plain fan switch, you mark one terminal as black and the other as red.

Now, hook like colors together.

I don't understand how to hook colors together if the switch doesn't provide an on-board splice point for that many wires.

Then you use "Wire Nuts" generally, or you can use Wago style "lever connectors". You probably want a red wire nut to connect as many blacks as you'll have to connect.

But one of the blacks is not a wire. It's a switch terminal screw.

You need to use a technique called a pigtail. For this you need a few scraps of wire. Buy 1 foot of 12/3 Romex, and cut it into two 6" sections and then peel the sheath off of it. That'll give you a supply of pigtails in a variety of colors.

I use pigtails pretty much by default. If I know my switch needs to go between black and red, I'll stick a black and red pigtail on the switch. This often makes for some redundant connections, but I don't care, and they work fine.

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