Connectors

Connector choice is a key part of wiring harness design. Badly chosen or badly assembled connectors can often be the source of electrical issues that are annoying to fix while testing the car, so care should be taken to choose the right connector and the right tools to assemble and disassemble it.

Housing

Weather Sealing

Connectors are usually rated with an IP code. Connectors that are open to the elements (which is most of them on a formula car) will need to be rated accordingly.

Retention

All connectors feature some sort of retention method. For most connections in a FS car, strong retention methods (locking or tight friction-fit) are required. Only a few applications (e.g. connection between ECU and computer for tuning) may benefit from connectors with weak retention.

Friction Fit

Friction fit connectors rely only on the friction between the mating connectors for retention. Friction fit is common in consumer connectors such as USB, but is often unsuitable for the conditions in a FS car. With repeated connect/disconnect cycles, a friction fit connector may wear down, decreasing holding force.

Locking Tab

Connectors featuring a locking tab are very common in automotive applications. Some locking tabs can be operated by hand, while others may require a tool to open. A common example of a connector with locking tabs is the Deutsch DTM series.

Screw Lock

Screw lock connectors use a threaded screw to retain the connector. While generally resilient, some screw lock connectors can loosen in high vibration environments, especially if not torqued enough. However, over torquing of screw lock connectors can make them difficult to remove. A common example of a screw lock connector is the Binder M9 series.

Twist Lock

Twist lock connectors operate similarly to screw lock connectors, however, they feature a mechanism that locks the connector with fewer rotations than a screw lock would require. Twist lock connectors have the benefit of being faster to operate than screw lock connectors, as well as having a hard stop, leaving no doubt as to whether the connector is under or over tightened. A common example of twist lock connector is the Deutsch AS series.

Cam Lock

Cam lock connectors use a cam to pull the two mating connectors together. This ensures that all contacts are seated properly, and prevents the connector from coming loose over time. An example of a cam lock connector is the Molex M123 series.

Push-Pull

Push-pull connectors require that a sleeve on the connector be pulled back in order to release the locking mechanism. Some connectors require the mechanism to be unlocked when connecting or disconnecting the connector, while others only require this during disconnection. The most common push-pull connectors are made by LEMO.

Contacts

Connection Method

Crimp

A crimp is a mechanical connection between wire and terminal. The terminal is deformed tightly around the wire conductors, often with additional points secured to the jacket for strain relief. When done properly, this can be an incredibly strong connection - sometimes stronger than the wire itself. For this reason, most professional motorsport wiring harnesses will only use crimped joints. To achieve a reliable crimp, terminals must be properly designed for the wire gauge being used. The correct tools are also necessary; using pliers or a vise will almost always result in a weak connection that is more likely to fail.

Solder

Soldering is the process of joining two or more parts by melting solder around the connection. When the solder cools, it creates a good electrical connection and a weak mechanical connection. Solder joints are much more brittle than crimped joints, so they are unreliable in high-vibration environments.

Screw Down

Screw terminals use a screw to clamp onto wires. Unlike crimp and solder connections, screw terminals do not permanently or semi-permanently fasten wires, and therefore are good solutions for applications such as an engine dyno or test bench.

Types

Free Hanging

This is probably the most common type of connector on an FSAE car. These connect directly to wires or cables, and can interface either with other free hanging connectors or with panel mount connectors. In FS these will usually need to be weather resistant. The Deutsch DT and DTM series are popular in FS, although many varieties exist.

Panel Mount

Panel mount connectors are often used to allow a circuit inside of a housing, such as a PCB, to interface with external devices. In FSAE these will usually need to be resistant to the weather. They can either be soldered directly to a PCB, or they can be connected to a circuit via wires.

PCB Mount

These are connectors that are soldered to PCBs. They are usually not weather resistant, and are only used inside a housing - either to connect two PCBs, or to connect a PCB to a standalone panel mount connector.

PCB to PCB

PCBs can be directly connected together inside a housing without the use of wires. This is usually done for modularity (so that you can use a PCB for multiple functions), interfacing with a premade part (e.g., a microcontroller), or for packaging reasons. Care needs to be taken so that the solder joints on the connectors are not being overly stressed with the weight of a PCB.

OEM Connectors

Many off-the-shelf parts either come with a pre-attached connector, or have a connector integral to the part itself. Some parts include a mating connector, while others will require one to be sourced. OEM connectors intended for mass production often have significantly lower connect/disconnect cycle ratings than other connectors.

Considerations

Density

Connectors can vary greatly in how close together the pins are. A connector with a higher density will usually be lighter and easier to package, but they can be more expensive and harder to assemble.

Connect/Disconnect Cycle Rating

As connectors are connected and disconnected, the contacts and components will deteriorate. The cycle rating is how many times this can happen while still meeting the specifications for minimum resistance and pull force. Many connectors (like board to board connectors) are only rated to tens of cycles, while some (like USB connectors) are rated for thousands of insertions.