Bosch relay vs. fog lamp relay...difference?

[MaxPatten]

Hey I'm doing my fuel pump rewire this weekend and read on vfaq that you need a Bosch relay. I went to crappytire and got one of their fog lamp relays...my question is, on the vfaq they say the Bosch relay has an 87 & 87A (which isn't used) and the fog lamp relay I bought has 87 & 87. Does that make a difference since 87A isnt used, and does it matter which 87 connection I use?

Thanks

[Martin Raska]

Sounds strange.  Do you have a multimeter that you could use to figure the continuity between the terminals?  Does this other 87 replace the 30 or do you still have a 30?

If you really want to figure it out, post the make and model of the relay (hopefully says on it) and we can look up the pinout and figure it out.

[MaxPatten]

Ya it still has all the same connections (85/86/30) and also the 2 87s. Someone told me today that the relays are all the same...to just use the 87 that sits in the same position on the relay as 87A would...

[Martin Raska]

It's actually not strange at all I just wasn't thinking I had just woken up and your "all relays the same" comment triggered my brain.

If it's a fog lamp relay it likely has the two so it uses a single relay for dual fogs, so the 87s are both 87s.  You don't have a 87a terminal because it is a ST (single throw) relay rather than the conventional relay which is a SPDT (single pole double throw).  Yours sounds like a single pole so that shouldn't add any complication.

So don't wire it up based on pin position, but wire it up based on the correct pin alphanumberical pin designations.  All relays you find will be of the same basic idea composted of poles and throws/switches, but they can differ in the number of poles and throws, as well as having pins in parallel like it sounds like this fog lamp one you found has.

[MaxPatten]

Alright cool...so I'll just wire it up to the 87 and be good to go. Just wasn't sure if I'd need to go and get a different relay with an 87A (even though I wouldnt have used it anyways)

As always, thanks for your advice :banana

[Martin Raska]

You'd only want 87a if you wanted another connections when the fuel pump was off being triggered by the same relay.  Say a light that was toggled when the fuel pump's status was changed by using the same relay to switch both.  In other words, the 87a just adds a connection in that is closed when the relay is not powered at all, where the relay you have sounds like it is just a pure switch, open or closed, rather than 2 mutually exclusive connections switching from open to closed.

[John Hartman]

all this said, and correctly, I will add that I would suggest you use a good Bosch relay anyways, you don't want some cheap CT fog light relay failing sometime down the road on your fuel pump.

just my 2 centavos.