Relays

[Donnie]

In your view, on what circuits are relays mandatory? Thanks in advance 

[CarlB]

All depends on what the amp rating the switches you are using. The wire is important as well, but generally the switch is the component with the low rating.  

[Marek]

Switches, connections, and long wire runs are your most likely sources of either current drop or over-heating (the prime motivators for using relays).

 

As a general rule, that means beams (front lights), fans, and pumps.

 

You can also generalize to say any circuit which is 14AWG or larger; assuming your harness was appropriately sized.  If you are replacing the wires, this list is a decent rule of thumb on wire gauges for motorsports:

Automotive use (longer wire runs ) 10/14/20AWG:

Battery Positive Direct 10AWG
Battery Negative Direct 10AWG
Other Battery Positive 14AWG
Fuel Pump Positive 14AWG
Radiator Fan 14AWG
Switched Ignition 20AWG
12V 5A Fused 20AWG
Tach Output 20AWG
Sensors 20 AWG
Injectors 20AWG

 

For motorcycle use (short wire runs) 14/18/16/20/22AWG:

Injectors 20AWG (better seal plugs)
Lambda Sensor (5) 20AWG to Autosport
Lambda Harness: 12V+ 20AWG, Heater(-) 20AWG, Vs 22AWG, Ip 22AWG, Lambda Analog GND 22AWG
5V Sensors 22AWG; Fuel Pump +/- 16AWG
VBat+ 14AWG
Chassis Ground VBat- 14AWG

 

References:

 

https://dsl.torque.net/tech/relays/relays.html

 

https://www.rbracing-rsr.com/wiring_ecu.html

 

 

[jbcollier]

Can’t give advice without an application.  A pre-crossflow with a 20 amp generator and a pair Webers is a completely beast to a fuel injected, Duratec with all the mod-cons.

[Donnie]

Funny. You had plenty of erroneous advice to give when my Series 1 was on BAT.

[jbcollier]

More to hand, no worries.

[Donnie]

I can't wait.