Load Cell Wiring and Trimming: Color Codes and Step-by-Step Guide
Updated October 21, 2026
The short answer: a load cell has four or six wires: two excitation wires that power it, two signal wires that carry its output, and on six-wire cells two sense wires that let the indicator correct for voltage loss in long cables. Wire colors aren't standard between makers, so always wire from the load cell's own datasheet. Trimming is how a technician balances the load cells in a junction box so the scale reads the same wherever the load sits. Below: 4-wire vs 6-wire, color codes, the two trimming methods, the trimming steps, and signs your scale is out of trim.
This guide won't make you a certified technician. It will help you spot a problem early, describe it accurately, and make better decisions when it's time to service or replace parts.
Load cell wiring: 4-wire vs 6-wire
Every strain-gauge load cell has at least four wires:
- + Excitation and − Excitation: supply power from the indicator to the load cell.
- + Signal and − Signal: carry the load cell's small output voltage back to the indicator.
A six-wire load cell adds + Sense and − Sense. These connect to the indicator's sense terminals, sometimes through a junction box, and report the voltage actually reaching the load cell.
Why it matters: voltage drops over long cable runs because of wire resistance, and the drop changes with temperature. In a four-wire system, that drop goes unnoticed and quietly takes away accuracy. In a six-wire system, the indicator sees the drop through the sense lines and compensates. For long cable runs, outdoor installs or precision-critical weighing, six-wire is the safer choice. If you connect a four-wire cable to an indicator with sense terminals, the indicator manual will show how to jumper the sense terminals to excitation.
Load cell wire color codes
Wire colors identify each line, but they are not standardized across manufacturers. A color that means + Signal on one brand can mean something different on another, and some makers use different colors on different models. Before making any connection, get the wiring chart for the exact load cell model, from its datasheet, label or manufacturer.
For Rice Lake load cells, Rice Lake publishes an online load cell wiring guide that technicians can use during installation and troubleshooting.
A common cause of trouble after a repair: if a scale reads negative when you add weight, or won't respond at all after a load cell swap, the first thing to check is a reversed signal pair or a cell wired to the wrong junction box terminal.
What is load cell trimming?
A typical floor scale has four load cells, one under each corner. In theory each carries a quarter of any load. In practice it never works out exactly:
- Load cells come out of the factory with slightly different outputs. Two cells with the same part number won't match exactly.
- Weight reaches each corner differently depending on where the load sits, how level the floor is and how the frame flexes.
Left uncorrected, the reading depends on where the load sits, not just how heavy it is. Trimming fixes that. The signals from each load cell meet in a junction box, where adjustments balance the outputs before one combined signal goes to the indicator.
In tank, hopper and vessel weighing it matters even more. Agitators, uneven material flow and buildup change how weight reaches each load cell, and an untrimmed system piles up errors over time.
Excitation trimming vs signal trimming
Both methods use the lowest-output load cell as the reference and bring the others down to match it. They differ in what they adjust.
| Excitation trimming | Signal trimming | |
|---|---|---|
| What it adjusts | Adds resistance in each cell's excitation (power) circuit, lowering its supply voltage | Adds a high-resistance parallel path across each cell's signal output, bleeding off a controlled part of the signal |
| Temperature stability | Resistance shifts with temperature, so the trim can drift where temperatures swing | Holds up better under temperature change and vibration |
| Where it's used | The older method, still used on some systems and indicators | Today's default, compatible with nearly all indicators |
| Example junction box | JB4ES TuffSeal excitation trim | JB4SS TuffSeal signal trim |
Use the method your junction box and indicator are designed for. If you're replacing a junction box, match it to the indicator's requirements.
How load cell trimming is done, step by step
This is how a technician trims a four-cell floor scale with a signal-trim junction box. Excitation trimming follows the same pattern. Trimming affects the scale's accuracy and, on a legal-for-trade scale, its certification. It should be done by a qualified scale technician, and a legal-for-trade scale has to be tested and sealed again under your state's rules (check with your state weights and measures office).
- Check the basics first. Confirm all load cells have the same capacity rating. Inspect every cable and connection for damage, moisture or corrosion, and make sure the scale sits level with nothing touching the deck. Trimming won't fix a damaged cable or a failing cell.
- Set up the junction box. Following its manual, set the jumpers for the number of cells in use and turn every trim potentiometer to the "no trim" position, so all cells start at full output.
- Zero the empty scale at the indicator.
- Corner test. Place the same test weight over each load cell in turn, as close to the corner as possible, and write down each reading. Use a weight large enough to read clearly and well within the scale's capacity.
- Find the reference. The corner with the lowest reading is the reference. Don't adjust it.
- Trim the others down. Move the test weight to each of the other corners and turn that corner's potentiometer until its reading matches the reference.
- Repeat. Adjustments interact, so re-zero and repeat the corner test until all corners agree within the scale's tolerance.
- Calibrate the span. With the corners balanced, calibrate the indicator with certified test weights, then run a final corner test and an increasing-load test.
- Close and seal. Close the junction box with its seal intact, and for legal-for-trade use, have the scale inspected and sealed.
Signs your scale is out of trim
A trimmed scale reads the same wherever the load sits. When it's out of trim, or something else is wrong, you'll see:
- readings that change when the same load moves from corner to corner;
- a scale that passes calibration in the center but fails at the edges;
- zero drift that wasn't there before.
Those signs don't always mean a re-trim. A nicked cable, moisture or corrosion in the junction box, debris under the deck, or one load cell starting to fail can all look the same. Describing the exact symptom ("reads 12 lb light on the back left corner") saves a technician time and you money. For floor scale care in general, see our scale maintenance tips.
Junction boxes and replacement load cells
If a junction box is corroded or damaged, or a load cell has failed, replacing the part and re-trimming is usually faster than chasing intermittent readings:
- Junction boxes: Rice Lake signal trim boxes such as the JB4SS (from $354), excitation trim boxes such as the JB4ES (from $355), the iQUBE³ digital diagnostic junction box (from $1,632), and our SL-JB stainless junction box (from $161.99). See all Rice Lake junction boxes.
- Load cells: replacement shear beam load cells such as the GX-1-2T-C3 (from $114.99), complete load cell kits, and the full range of Rice Lake load cells.
Prices from selletonscales.com on October 21, 2026. The product page always shows the current price.
When replacing one load cell in a set, match the capacity and type of the others, and plan to re-trim and recalibrate afterward. For how load cells work in a scale, see our load cell scale technology guide and our industrial floor scale guide.
Load cell wiring and trimming FAQs
What is the difference between a 4-wire and a 6-wire load cell?
Both have two excitation wires and two signal wires. A 6-wire load cell adds two sense wires that let the indicator measure and correct for voltage loss in the cable, which keeps long cable runs accurate.
Are load cell wire colors standard?
No. Colors vary between manufacturers and sometimes between models. Always wire from the datasheet or label for the exact load cell you're using.
What does load cell trimming do?
Trimming balances the outputs of the load cells in a multi-cell scale, usually in the junction box, so the scale reads the same wherever the load is placed on the platform.
Is signal trimming or excitation trimming better?
Signal trimming is the more common method today. It works with nearly all indicators and holds up better under temperature changes. Use the method your junction box and indicator are designed for.
Can I trim my scale myself?
Trimming and calibration affect accuracy and legal-for-trade certification, so they should be done by a qualified scale technician. A legal-for-trade scale must also be tested and sealed under your state's weights and measures rules.
Need parts or help?
Shop load cell kits and junction boxes, or call SellEton Scales at (844) 735-5386 or send us a message with your scale model and the symptom you're seeing.