Where should I take the chassis (ground) connection of the lift retrofit kit from?
Take the negative to bare metal truly bonded to the chassis, using a serrated washer; match the cross section of the positive line and verify by measuring.
Connect the negative (ground) terminal, with a serrated washer, to a point whose paint and rust have been cleaned back to bare metal and whose body really is electrically bonded to the chassis of the vehicle. The cross section has to be the same as that of the positive supply wire — thinning the negative line makes the cross section calculation done on the positive side meaningless. If there is no reliable chassis point nearby, the second option is to run the negative terminal straight to the negative terminal of the battery.
How to choose a good chassis point
Not every tightened bolt is an ground. Look at the following in order when choosing the point:
- Make sure it is true chassis. Panels mounted on rubber blocks, plastic parts and painted body panels do not give a reliable return path.
- Prepare the surface. Sand off the paint, rust and coating; after making the connection, apply a suitable protective to prevent corrosion.
- The fastener. Use a serrated washer and a bolt tightened to the proper torque; prefer a locking nut against working loose under vibration.
- Keep the distance short. The closer the chassis point is to the kit, the lower the resistance.
- Do not use a shared point. Avoid sharing the same bolt with high-current consumers such as the starter motor.
Verify the connection by measuring, not by looking
A well-tightened bolt looks like a sound connection to the eye; if there is paint, rust or oxide underneath it, it is not. The method of verification is simple: with the kit drawing load, measure the voltage difference between the negative terminal of the kit and the negative terminal of the battery. If the two points are electrically the same point, the difference stays at the order of the measurement uncertainty; as the difference grows, the voltage reaching the kit falls, because every millivolt lost is spent in the resistance of the connection. The steps of the measurement are described under the voltage drop test with a multimeter.
If the difference comes out large, split the measurement in two: first between the negative terminal of the kit and the metal the washer sits on, then between that metal and the negative terminal of the battery. If the difference shows up in the first measurement, it is the wire, the lug or the grip of the washer; if in the second, the chassis path itself is at fault. That distinction saves you from replacing a sound wire for nothing.
A chassis point or the battery negative direct
| Method | When it is preferred | What to watch |
|---|---|---|
| A chassis point nearby | If heavy body and bare metal can be reached beside the kit | Surface preparation and corrosion protection are essential |
| The battery negative terminal direct | If there is no reliable point nearby, or the body is painted or separated on blocks | The wire gets longer; cross section and route are planned accordingly |
The choice between the two is usually settled by distance; the detail of the subject is under whether the negative should be taken from the battery or the chassis. Whichever route you choose the cross section rule does not change, so supply wire cross section holds for the negative line as well.
Where this account does not hold
- Positive-ground vehicles. On some very old vehicles the positive terminal is connected to the ground; there, everything described here turns round. First confirm which terminal the ground is connected to.
- A washer tightened onto a painted surface. Paint is a good insulator; a connection on an uncleaned surface can work on the first day and fail afterwards.
- Welding and jump-battery work. If welding is to be done on the vehicle, current travelling along the ground path can damage the electronics; that job is done with the kit removed or its supply disconnected.
The order in practice is this: choose the point, open the surface back to bare metal, tighten the serrated washer, apply the protective, then run the kit and measure the voltage difference. Behind one of the most common complaints, the motor turning slowly or weakly, what usually lies is not a kit fault but this connection; the measurement takes a minute and comes before changing parts.
The full topic: Converting a tractor hydraulic lever to electronic control