Contact 87a should be energized when the pump is off. A single pole double throw relay bounces its pole between two contacts. One N/C (normally closed) and the other is N/O (normally open). So if you want to know when the pump is off, then connect a lamp to that contact. That is, if the relay is wired internally for 87a. Some don't even have a 87a contact, so they are single pole, single throw relay. In the pic bellow, 87a is the upper N/C contact, you connect the pump to the N/O contact, so when the relay receives power in its coil, it makes contact to the lower N/O contact, activating the pump/lights/fan, etc.
http://www.angelfire.com/ab6/userper/relays.htm

 

good stuff, that goes in the electrical basics sticky right now.

 

Ok easy enough. Wire either NC or NO. thanks.

 

Remember, N/open will close when the relay is activated, and N/close will open. You'll want to connect the accessory to N/O.

 

I always use an ohm meter between 30 and 87 / 87A. Whichever pair shows continuity is the NC pair and the other is NO.

 

does anyone know what to ask for at the parststore to get the relay? Autozone or advance is all we have around here and it seems that you can't get anything from them unless they can look it up in their computer.
is there an application to ask for to get this relay to use for the NSS?
Thanks,
Rob

 

just go to Radio Shack if you have one it will be much easier

 

This link may be useful in helping you visualize what is on the inside. Look for the simple schematic of a SPDT relay about midway down. http://wolfstone.halloweenhost.com/TechBase/cmprly_Relays.html#What

Once you have a visual understanding of the guts, the pin layout on the Bosch relay is intuitive - except for the pole contacts.

The vertical contacts 85 and 86 are the coil contacts. *Usually* it doesn't matter which one of these are connected to power or ground BUT some relays have a diode accross the coil to help suppress flyback voltages when the coil de-energizes. As a result, it's worth checking the documentation. A simple test with a DMM might help you determine if it has a relay accross the coil or not.

The relay toggle (common) connection is the lone connection all by itself at position 30.

The pins 87 and 87a are the NO and NC connections respectively. In my mind, the positions of these terminals are reversed. This link http://mymiata.paladinmicro.com/MiataRelays.htm shows some bosch relay guts that may help understand the internal layout.

Anyhow, once you're familiar with the internals, you can pretty much look at any bosch relay and know how to hook it up from memory. As I was saying before, I always use an ohm meter between 30 and 87 / 87A. Whichever pair shows continuity is the NC pair and the other is NO.

 

Thank you for the*informative*posts.

 

Thank you for the*informative*posts.