Difference between 4 pin and 5 pin relays?

[Jon K]

the main on most bmws has 2 87s to power more then one circuit. to wire a 4 pin simple relay hook the 30 to the battery, through a fuse if you want the circuit protected, 87 goes to what you want to power up and how you switch it depends on how you want to wire the system, to turn on the relay you need to get ground and power to 85 and 86 (doesn't really matter which gets - or +) you can jumper power from 30 to 86 and actuate the circuit with a ground to 85 or run 86 directly to ground and run a power to 85 to actuate the circuit. 4 or 5 pin depends on if you want any options, like a 2nd 87, a 87a that's powered up with the relay open (powers off when you turn on the relay) a indicator light or whatever

Thanks Winfred - here's my issue - with my aftermarket ECU I am tapping the switch +12v on the main relay for power to the ECU. When I shut the car off it keeps running until fuel pressure runs out (fuel pump turns off with key but it seems the main relay is holding closed for a while). I am thinking of making my own "main" relay. What do you think I should do?

[zygoteer]

What is the source of the picture. Looks like a book/manual worth purchasing.

It is not a manual you can buy ... it is from my archive of collected data over the past 40 years or so.
The early half has been converted to pdf and the rest is electronic anyway, now in the form of Word and Excel files.

Thanks Zygoteer - let me ask a cheater question. I did read your post... but...

Why would the main relay have a 5 pin relay?

More importantly, I want to make a relay that supplies 12v to an object when the ignition is switched on. I know where to find the ignition wire, I know where to find ground points, and I have a couple +12v constant sources in there, so how would I set up a relay and would it be a 4 pin or 5?

It is very possible that a main relay could be like any of the contact layouts shown; I can think of reasons for all scenarios.

However, to achieve what you say, you could use any of the '5-blade' types in the picture or the '4-blade' type with 'NO' contacts.
Just wire the ignition +12volt to '86', vehicle ground to '85', battery +12volt to '30', then '87' to the positive contact on the device you wish to switch, with the other side to vehicle ground.
If your relays don't have all the markings, use a multimeter to check out which contacts are connected or not, bearing in mind that the coil resistance is likely to be in the range of 50 to 1000 ohms.