Should I connect the lift retrofit kit directly to the battery or to the ignition supply?
Run the power line straight from the battery, fuse close to its terminal. If ignition control is wanted the signal feeds a relay coil, not the power line.
Running the power line straight from the battery, with the fuse close to the battery terminal, is the soundest method; the LFT20 draws 10A on average and the thin wires in the ignition circuit were not designed to carry that load. If ignition control is wanted, that signal is fed to a relay coil and the power still comes from the battery. The kit is then left dead when the ignition is off, and the voltage drop is kept low as well.
The three options compared
| Method | Advantage | Drawback | Who it suits |
|---|---|---|---|
| Straight from the battery | Lowest voltage drop, most reliable operation | The line stays live even with the ignition off | A tractor in frequent use that is not left out of sight |
| Ignition controlled through a relay | Both a low voltage drop and complete deadness with the vehicle switched off | One relay and a little extra wiring | The recommended solution |
| Straight off the ignition circuit | The least wiring | The existing line was not sized for this extra load; the wire can heat up and the tractor's fuse can blow | Not recommended |
The deciding question is this: is it a risk for you if this line stays live while the vehicle is switched off? If the answer is yes, the relay arrangement is the only sensible route anyway. If it is no, connecting straight to the battery means fewer parts and fewer points of failure.
How the relay arrangement is built
A thin wire from the ignition supply feeds the signal to the coil of the relay, and the contact of the relay carries the fused heavy line from the battery to the kit. So the thin wire carries only the coil current and the heavy wire the motor current. When choosing a relay, take account of the current the contact will switch and the type of load; the entry on relay output explains how these figures are read. Fix the relay somewhere dry, protected from vibration and reachable when servicing. Do not take the coil signal from a terminal that is only live in the crank position; choose one that is live with the ignition on, otherwise the kit will only be energised while the starter is being turned.
Fuse and cross section
- Where the fuse goes: The fuse should be at the start of the line, as close to the battery terminal as possible. The reason is explained under why the fuse is placed closest to the battery terminal: the fuse protects the wire, not the device.
- Fuse rating: How the right value for the kit is chosen is under fuse selection for the LFT20.
- Cross section: The supply cross section has to be at least 2.5 mm² for a 10A load; as the line lengthens the cross section grows with it. The detail is under supply wire cross section.
- The negative terminal: The negative supply has to go to a clean metal chassis point; the chassis connection is at least as decisive as the positive line.
When connecting straight to the battery is enough
If the tractor is in daily use, if the switch is somewhere in the cab where it cannot be pressed by accident and if nobody can reach it while the vehicle is shut down, connecting straight to the battery causes no trouble. The real gain of the relay arrangement shows up during long periods parked and where the vehicle is left out of sight. Using the ignition line as a power line, against that, is not recommended under any circumstances; the wire you save is not worth the safety you lose.
What to do in practice
Settle the route and the position of the fuse before running any wire. If you choose the relay arrangement, take the coil signal from a terminal that is live with the ignition on, run the power line from the battery and clamp the two lines separately. When the installation is finished, press the switch with the ignition off and confirm that the kit really is dead.
The full topic: Converting a tractor hydraulic lever to electronic control