Relay's

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Billy1972
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Thu Feb 28, 2019 12:29 pm

Hi, I need to replace the relays for my Horn and Fog Light.

Total novice here so I do apologise in advance, but which ones do I change and where is best to purchase replacements or new ones.

1987 BMW 325i (E plate) Convertible

Thanks
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Brianmoooore
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Thu Feb 28, 2019 1:44 pm

Horn relay is K2, one of the orange ones, and foglight relay is K4 or K8, the black ones. Which depends whether you are referring to the front or rear foglight!
Orange ones are a fairly 'standard' relay which is available from many sources, including BMW. The black double pole relay is a bit less common, but still should be readily available from the same places.
What makes you think you need new ones? It's very rare for a simple relay like these to fail, and when they do, it's a minute's job to open them up and clean up the contacts.
If you really do need to replace them, second hand genuine ones should be fine.
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Billy1972
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Thu Feb 28, 2019 4:26 pm

Thanks so much for the info it really is appreciated.

Neither the front nor the rear fog lights worked when I picked it up, so I replaced the twin fog light switch and now the rear orange and front green alluminates on the dash.

The rear fog is now working and lights up but the front fogs are not coming on? It's not the fuse or the bulbs so I'm thinking it could be the relay so was going to see if I can source a replacement? Would it be a K4 or K8?

The horns aren't working also, again I've checked the fuses and even bought a replacement centre section on the steering wheel and still nothing, so again thinking it may be a relay?

What do you think?
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Brianmoooore
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Thu Feb 28, 2019 7:19 pm

If the front fog tell tale on the dash lights up, then there's nothing wrong with the relay or fuse 29 - the tell tale connects to the 'out' side of the fuse, along with the left front foglight.
Relays are just electrically operated switches. The control circuit (switch, etc.) operates the relay, and the switch part of the relay operates the power circuit (the lights, horn, etc.) The control circuit is easily tested by turning the relay on (with the control switch) and unplugging and plugging it in. It should click when you remove it, and again when you refit it.
The power circuit an be checked by pulling out the relay and using a short piece of wire to link together the appropriate pins of its base. These are pins 30 and 87 for the horn relay, and 30, 87 and 87b for the foglight.
With these links in place you need to disconnect the plugs at the lights and horn, and connect a 12 volt lamp across the two pins in the plug. The lamp should light. If it does, the problem is with the horn, or inside the case of the foglight.
If it doesn't light, connect the test lamp between the pin in the plug that is NOT connected to the brown wire, and a good body earth. If the lamp now lights, there is a problem with the earth return to the horn or lamps - most likely where they all connect to the body at the front of the left inner front wing.
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