Join Date: Mar 2002
Location: Austin, TX, USA
Sorry ismail, I can help with relays but can't decode your question. Let me elaborate on how relays work and hopefully lead you to an answer.
87a and 87b are most likely terminal lables on the bottom of the relays. Usually, there is at least one pole with a terminal for the toggle, and a terminal for the normally open (NO)contact and normally closed (NC)contact. This is known as a single pole double throw relay (SPDT) and they usually have 5 terminals on the bottom (2 for coil, and 3 for the toggle/NO/NC connections) Your ohm meter will locate the normally closed circuit (between pole toggle and contact terminal) by showing up as a dead short on your meter. The remaining terminal has to be the normally open terminal. You'll have to energize the coil to get a reading on your meter though.
Some relays have two poles as well as the NO and NC terminals for each pole. These are known as double pole double throw (DPDT) and have 8 connections on the bottom.
There are many variations on the theme such as single pole single throw (4 terminals), double pole single throw (6 terminals), and custom configurations. The DPDT and SPDT varieties are most common. As for 87A and 87B, use an ohm meter to see if they have resistance between them (about 100 ohms I'd guess). If so, they mark the coil terminals. Otherwise they should show a short circuit to another terminal in which case the other terminal is probably the toggle and the 87A/B terminals are the normally open and normally closed contacts.
Once you have mapped out the relay in question, you should be able to determine how you can wire it into your circuit. Also, you'll find that most all relays have their terminals arrange such that you can tell what is what. For example, the two coil terminals will face one another while the three pole terminals will be facing one another in the opposite direction. Of the three pole terminals, the toggle is usually offset from the two NO/NC terminals.