I've previously used a relay to power heated grips on my motorcycle using an existing ignition circuit. It worked well, but my research into the actual relay I bought consisted of going to Radio Shack and buying the first 5 terminal relay I saw. I am currently wiring a fan switch for a different motorcycle. The bike has a temperature activated circuit but I'd like to have control over the fan in traffic, off-road, etc. I'm going to use an existing accessory circuit that is energized when the key is turned "on" for the coil, and then run a new wire to the battery for power; about as simple a use for a relay as can be. But, I have a few practical questions:
1. Any major advantage to using a 5 terminal relay vs. a 4 terminal relay? I suppose the "normally closed" position would allow me to bypass the coil if need be.
2. Do I really need a relay advertised as "waterproof?"
3. Bosch sells a "micro relay" rated at 30 amps. Although I initially thought it would be good to use something smaller, I get the impression that it's not really meant for this type of application. Anyone have any advice/experience?
4. Would a connector harness be a good idea for this type of application? This relay may be under the headlights so I'm more concerned about this application than my previous one (relay was under the seat).
Thanks much folks.
There are two types of 5 terminal relays. They both of course have the two coil terminals. One type has two normally open terminals (labeled 87) and one common (30). This is sometimes used for fog lights.
The other has one normally open (87) and a normally closed (87a) plus a common (30).
Either relay will work as you only need the coil terminals plus one 87 and a 30.
I strongly suggest a socket and a waterproof relay or they may be covered in ZIP 'Seal n Peel' (a transparent sealant which looks like silicone and can be found at most hardware stores - the advantage over silicone is that it can be peeled if need be). The terminals may be covered in di-electric grease to protect from corrosion.
Try to protect the relay from vibration. Relays have small springs which keep the contacts apart and can open/close from the engine vibration or driving over rough roads. Mounting them upright is best.
-------------
Prepare your future. It wasn't the lack of stones that killed the stone age.