Splicing a Weigh Bar Cable
Cables are the most common failure on a grain cart scale - far more often than the weigh bar itself. Most can be fixed with a soldered splice. Practice one here first.
Draft - not yet approved
Loading the practice splice... If nothing appears, call 800-582-3175.
Before you cut
- Make sure it's the cable. Unplug the bars at the junction box and plug them in one at a time - the one that makes the weight jump or run away is your suspect. Then meter it: a pair with no reading means a broken wire in the cable. See testing a weigh bar with a meter.
- Find the damage. Flex the cable slowly along its length with the meter on a pair - the reading jumps or drops out at the break. Look hardest where cables get chewed, pinched or stretched: along the frame, at the walker on a walking tandem, at the hitch on sharp turns, and under clamps.
- Turn the scale off first so unplugging and plugging in doesn't record false loads.
The splice, step by step
- Cut out the damaged section. Keep cutting back until the copper is bright. Green, black or wet copper means water has traveled up the cable - keep going.
- Strip the outer jacket back about 1-1/2 to 2 inches on each end without nicking the wires inside.
- Slide the big heat shrink tube on now, over the whole cable and parked away from where you'll solder. If you'd rather shrink each joint than tape it, slide a small tube onto each wire too. Forget the big tube and you'll be cutting the splice back out.
- Strip each wire about 1/2 inch.
- Join color for color - red to red, black to black, green to green, white to white, bare shield to bare shield. Stagger the joints so the splice doesn't end up as one big lump.
- Solder each joint with rosin-core solder. Heat the wire, not the solder, until it flows into the twist and goes shiny. Dull and lumpy is a cold joint - reheat it.
- Tape over each joint (or shrink a small tube over it) so no bare copper can touch another wire.
- Test it before you seal it - meter it at the junction box end. Each pair should read about 350 ohms, the same as before the cable was damaged - the length of cable you cut out doesn't change the reading. The bare shield should read open to every wire.
- Seal it. Slide the big tube over the whole splice and shrink it to keep water out.
- Plug it in, zero and stand on the bar. It should read about your weight. A negative number means two wires in the same pair got swapped.
Which wires pair up
A splice is always color for color, so the brand doesn't change how you join it - but it does change which wires you meter together afterward.
| Bar brand | 350-ohm pair | 350-ohm pair |
|---|---|---|
| Weigh-Tronix | Green to black | White to red |
| Digi-Star / Agrimatics (Ezi-Mate) | Red to black | White to green |
Across pairs reads about 262 ohms. If a pair reads 262 after a splice, two wires from different pairs got crossed. More in junction box wiring and color codes.
What not to do
- No wire nuts, and never leave the splice with tape alone on the outside. Water gets in, and the scale starts drifting after the next rain. Tape over each joint is fine once the big heat shrink seals over it.
- Solder is best. Crimp connectors with heat shrink are second best.
- Don't calibrate around a bad cable. Fix it first, then check the scale by standing on the tongue and weighing around.
Parts: splice kits ($45). If the damage runs right up to the weigh bar, or water has corroded the copper all the way back, the bar may need replacing - call 800-582-3175 and we'll help you decide.
More help: grain cart scale troubleshooter · Libra won't weigh right? Start here
The simulation is simplified practice, drawn by us - not real readings.