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.

Contacts

Connection Method

Crimp

When crimping a terminal, you are essentially making the terminal clamp down onto the wire. 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 good crimp, you need to have sized your connectors for the wire gauge you are using. You will also need the correct tools - 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 an OK mechanical connection. Unlike welding, where two pieces of metal are melted to become one, soldering merely attaches two metals together. Solder joints are much more brittle than crimped joints, so they should only be used on PCBs or to reinforce an already crimped connection.

Screw Down

With screw terminals, the wire is held in by the tightening of a screw. They are not positively locking, and are not weather resistant, but they can useful for prototyping in the shop or wiring up an engine dyno since they make it easy to swap wires around. If you need to splice multiple wires together on a vehicle, crimp splices are easy to use and much more durable.

Types

Free Hanging

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

Panel Mount

Panel mount connectors are used to allow a circuit to interface with the rest of the car. 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. They are commonly refered to as JST connectors: however, JST is not a standard but a manufacturer that makes many different families of PCB mount connectors.

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

Often you will not be able to choose your own connectors, and you will be restricted to what the manufacturer of a component decided to use. Many sensors have a connector molded into the housing, as do the coils and injectors on an IC car. ECUs and motor controllers are notorious for having connectors with seemingly millions of pins, and which connector they use should be taken into consideration when deciding on them. Megasquirt 3 ECUs, for instance, use DB37 connectors to interface with the car, which use soldered pins and are usually not waterproof.

When deciding on a component, make sure you can actually buy the connector it uses - often times they can be hard to find (or very expensive). A good source for the rare Japanese OEM connectors is cycleterminal.com

- their website seems to have been designed by cavemen but their prices are good.

Considerations

Density

Connectors can vary greatly in how close together the pins are. A connector with a higher density will usually be lighter, but they can be 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 maximum 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.