Low voltage remote control switching systems use a specific set of wire colors to distinguish between on pulses, off pulses, and common connections. These colors aren’t mandated by the National Electrical Code for Class 2 circuits, so they vary by manufacturer. Knowing which color does what is essential when troubleshooting, replacing relays, or adding switches to these systems, most of which were installed in homes between the 1950s and 1970s.
How GE Systems Are Color Coded
GE’s low voltage relay systems, including the widely installed RR7 relay, follow a consistent color scheme that became something of an industry standard. Red is the “on” wire, black is the “off” wire, and blue is the relay common. White serves as the switch common, connecting back to the switch panel. A blue-and-white striped wire carries 24 volts AC from the transformer, and yellow wires are reserved for pilot light circuits.
In practice, the three colors you’ll encounter most often at the switch location are red, black, and white. The red and black wires each carry a momentary pulse when you press one side of the switch, while white completes the circuit back through the common. At the relay itself, the blue wire is the common terminal that connects to the load side of the circuit. If you’re tracing wires through walls or junction boxes, remembering “red for on, black for off, blue for common” covers most of what you need for GE systems.
How Remcon Systems Differ
Remcon (later sold under the Amprobe name) used a similar three-wire logic but with a slightly different color assignment. To turn a Remcon relay on, you connect the red and white wires. To turn it off, you connect the black and white wires. White again serves as the common, and the basic on/off logic mirrors GE’s red-for-on, black-for-off convention.
One important detail with Remcon relays: when a single switch controls multiple relays on a single-phase three-wire service, all the black high-voltage wires from those relays must connect to the same hot leg. Mixing hot legs across relays sharing a switch can create a 240-volt fault. This is a wiring constraint, not a color-coding issue per se, but it’s the kind of mistake that becomes easy to make when you’re working inside a crowded relay panel and relying solely on wire colors to guide you.
Why Colors Aren’t Standardized by Code
The National Electrical Code governs wire colors for line-voltage circuits (black for hot, white for neutral, green for ground in the US), but it does not mandate specific colors for Class 2 low-voltage control wiring. These remote control switching systems operate at 24 to 28 volts AC, well within Class 2 territory, so their color schemes are set by the manufacturer rather than by code. Other low-voltage applications follow their own standards entirely. Network cabling, for example, follows TIA-568 color patterns that have nothing in common with relay wiring.
This means you cannot assume that a red wire in one system means the same thing as a red wire in another. If your home has a low-voltage switching system and you don’t know the brand, identifying the relay model is the first step before touching any wiring. GE relays are rectangular with a mounting tab, Remcon relays are typically cylindrical, and both are usually clustered near the electrical panel or in a dedicated relay cabinet.
Transformer Wire Colors
The transformer that steps household voltage down to 24 volts has its own color coding, and it’s separate from the relay wiring colors. On the primary (line voltage) side, you’ll typically see brown and blue wires connecting to the 120-volt supply. On the secondary (low voltage) side, black and yellow wires deliver the 24-volt output that powers the entire switching system.
If you’re replacing a transformer, matching the primary and secondary sides correctly matters. Reversing them would send line voltage into wiring rated for 24 volts. The secondary wires feed into the relay panel, where they connect to the blue-and-white striped bus wire (in GE systems) that distributes low-voltage power to every relay.
Practical Tips for Tracing Wires
In homes with these systems, decades of additions and modifications often leave wire colors less reliable than they should be. Previous owners or electricians may have spliced in non-standard wire, used whatever was available, or extended circuits without matching colors. A few practical habits help avoid mistakes.
- Test before trusting color. A multimeter set to AC volts can confirm whether a wire is carrying 24 volts (transformer output), a momentary pulse, or nothing at all. Color tells you what a wire is supposed to do. Voltage tells you what it’s actually doing.
- Label as you go. If you open a relay panel, use adhesive tags or colored tape to mark each wire’s function as you identify it. These systems can have dozens of relays packed together, and the original color becomes hard to read on aged insulation.
- Keep the system’s era in mind. Homes built in the 1950s and 1960s used cloth-insulated wiring that fades and discolors over time. A wire that looks brown today may have been red 60 years ago. When in doubt, trace the wire back to its terminal on the relay and identify it by position rather than color.
- Don’t mix manufacturers. GE and Remcon relays are not interchangeable without rewiring. Their color conventions overlap (both use red for on and black for off) but the relay terminals, mounting styles, and transformer requirements differ enough that swapping one for the other requires verifying every connection.
Two-Wire vs. Three-Wire Switch Runs
Most low-voltage remote control systems use three wires between the switch and the relay: on, off, and common. This is different from the two-wire and three-wire terminology used in standard line-voltage lighting, where the distinction refers to whether a neutral wire is present at the switch box.
In a traditional low-voltage three-wire setup, the switch is a momentary rocker or button that sends a pulse down either the on wire or the off wire, with the common wire completing the circuit. There is no continuous current flowing through these wires. The pulse lasts only as long as you hold the switch, and the relay latches mechanically into its on or off position. This is why low-voltage switches feel different from regular toggle switches: they spring back to center instead of staying flipped.
Some newer retrofit products designed to replace aging low-voltage systems use only two wires, combining the on and off signals through polarity reversal or digital encoding. If you’re upgrading switches in an older system, check whether the replacement requires two or three conductors, since pulling new wire through finished walls is often the hardest part of any retrofit.