relay socket pinout

[cak]

This is mostly for archival purposes, because I couldn't find the information anywhere. I hope it helps someone.

(I also have a question or two.)

I'm adding aux driving lamps, and I want to do it in the factory style - which I believe means above the bumper, using the "fog light" harness, hard wired in parallel with high beams. (Debate that or not - that's what I'm doing!)

My car didn't come with fogs, so the wiring is in the fenders, but there's no relay. OK, I pony up for 901-612-333-00-OEM from our host, and get



Neato. But what goes where? And why are there two wires with the same coloring?

Lots of searching, no clear results. Ohm meter and power supply...

30 - red
85 - brown
86 - gray
87 - red/white
87a - red/white

87a is normally closed (NC), 87 is normally open (NO); I want 87 for my purposes.

My understanding is that the convention is that 85 is always ground (this allows a red relay to work where a black one is) and that 30 is the source of load current (i.e., the battery). Is that right?

Is the convention to clip or otherwise hide the unused 87a lead?

Thanks.

[2.7RACER]

Chris,
With that relay connector I would trim 87a back and cap it with a small twist lock. Otherwise it will be "hot" when the relay is de-energized and you run the risk of it shorting to ground.
If you look at the other relay bases in your car, you'll find the unused pin sockets have been removed.
Remember to fuse the power going to pin 30.

[cak]

Thanks. I wonder if it's possible to pull out the unused 87a contact and wire without destroying the socket?

Remember to fuse the power going to pin 30.

As far as I can tell, the "factory way" is to fuse 87, for better or worse. My plan is to run the lead from 87 to the (currently unused) 16A fog light fuse, which is already connected to the harness going out to the wheelwells.

[2.7RACER]

Sounds like a plan to me. Keep in mind the "factory way" has led to electrical fires due to unprotected wiring.

[Early_S_Man]

Chris,

Considering the high replacement cost of that socket, and possible reuse in the future ... I suggest folding the unused #87a lead back and putting a couple of lengths of heatshrink over it for protection.

[cak]

Yes, shorts, fires, all a possibility. I guess that I could use a 50A breaker as a distribution point between the 10g going to the battery and the relays for low, high, aux. Worth considering. I was going to use a terminal block.

Warren, I may do the foldback. There are already a lot of wires in that region, and I was thinking of trimming very close to reduce the clutter just a little.

I really don't understand why the factory spec for this uses the same wire color for both 87 and 87a!

Thanks all.

[911pcars]

"I really don't understand why the factory spec for this uses the same wire color for both 87 and 87a!"

Here's a schematic of the relay:


This is generically a one-make, one-break relay; so called because the internal circuit between terminal 30 and 87A and 87 flops back and forth.

When the relay is not energized, 87A is "hot". However, when energized (current path through 86 and 85 is grounded), the connection from terminal 30 changes from terminal 87A to 87. They could have used a more identifiable red for one circuit and red w/trace for the other.

As Warren suggests, isolate and insulate the 87A wire if it's not used.

Sherwood

[cak]

They could have used a more identifiable red for one circuit and red w/trace for the other.

Yes, that was my point (except that they already used red for 30).

The schematic reading engineer in me says "same color, same function". Those red/white wires are just begging for trouble.