Rookie Fog Light Relay Question

SSTJ

SSTJ

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Hi all,

I'm wiring my first pair of fog lights. My 97 SE came absolutely bare, so there were no switches in the aux panel by the cigarette lighter. I bought a switch like this, and now realize I need a relay too. (The lights are 100W each, so I figure they'll draw up to 16 amps together.)

Can anyone point me toward the type of relay I should use? I'm completely new to this, and of course I'm getting all sorts of things in my Amazon searches.

With thanks!

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Results: These pictures from Jerry are worth 1000 words. Also this article for more about automotive relays. Buy a quality brand, like Bosch.
 
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Jerry Bransford said:
Has to be 12 volts DC of course. I can post a simple schematic tomorrow that would work.
Click to expand...

Thanks Jerry. Yes, any advice would be appreciated. As you saw on the link in my first post, the switch is a 3 wire pig tail:, hot in, load-out and ground.
 
The most common Bosch style 12 volt relay will work. Think of a relay as just a simple remote-controlled on-off switch.

The top animated diagram shows the lights as the "high current load". Wire the fog lights in parallel like is shown in the bottom drawing. The numbers on the relay in both schematics correspond to how the connectors are labeled on the relay. Your switch has the 'indicator' shown on both drawings built into it.


Driving light animated schematic.gif
Driving&FogLightInstallationDrawing.jpg
 
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Jerry Bransford said:
The most common Bosch style 12 volt relay will work. Think of a relay as just a simple remote-controlled on-off switch.

The top animated diagram shows the lights as the "high current load". Wire the fog lights in parallel like is shown in the bottom drawing. The numbers on the relay in both schematics correspond to how the connectors are labeled on the relay. Your switch has the 'indicator' shown on both drawings built into it.
Click to expand...

Jerry, this is awesome. We need @Chris to install a "tip" feature so I can PayPal you for such great posts. :) Thanks again; I'm excited to dig into this and do the installation.
 
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Hi again,

A few follow-up questions here.

1. As in the attached photo, the diagram that came with my switch has the wires for the #86 pins swapped. I assume that it’s ok to go either way?

2. Does the red wire on my switch’s pigtail really have to have a separate 12V power source? Can I not just tie that into the same wire that’s running from the battery positive terminal to the #30 pin on the relay? Just hate to run another wire all the way to the battery for the switch itself.

3. I could use a quick education on grounding. When is it safe to just ground to the frame or tie into another accessory’s ground wire? And when do I need to ground all the way back to the battery’s negative terminal? For instance, the black ground wire on this six switch I’m installing.

Thanks!

image.jpg
 
SSTJ said:
Hi again,

A few follow-up questions here.

1. As in the attached photo, the diagram that came with my switch has the wires for the #86 pins swapped. I assume that it’s ok to go either way?

2. Does the red wire on my switch’s pigtail really have to have a separate 12V power source? Can I not just tie that into the same wire that’s running from the battery positive terminal to the #30 pin on the relay? Just hate to run another wire all the way to the battery for the switch itself.

3. I could use a quick education on grounding. When is it safe to just ground to the frame or tie into another accessory’s ground wire? And when do I need to ground all the way back to the battery’s negative terminal? For instance, the black ground wire on this six switch I’m installing.

Thanks!

View attachment 195584
Click to expand...

Regarding #1 the answer is... It depends on the type of relay. If the relay has an internal resistor or diode, it does matter which is + and which is -. If it does not have a resistor or diode then it does not matter

Edit - for number 2. The positive wire for the relay coil can come from the fuse box behind the glove compartment. Use an add-a-fuse or similar to grab a wire that is powered with the key (accessory) so the lights turn off when the key is off. You don't want this coming directly from the battery
 
TrueTexas said:
Regarding #1 the answer is... It depends on the type of relay. If the relay has an internal resistor or diode, it does matter which is + and which is -. If it does not have a resistor or diode then it does not matter
Click to expand...

Interesting, thanks. Still on Question 1 here:

In both Jerry's image above, and also in the photo that I uploaded, the left pin says 86 while the right pin says 85. But on my relay, which is a 30A four-terminal with no 'center' pin, both the left and right pins say "86".

I guess I'm still wondering why Jerry's and the one in my photo have the left and right pins opposite. And as for the one I'm actually using (described above), would the arrangement make a difference?
 
I'd look at the relay carefully. There should be an 85 and 86. Sometimes they can be very hard to read. Does the relay have a diagram on the side or top? This diagram will indicate if a diode or resistor is inside the relay on the coil
 
The relay can be drawn multiple ways. I wouldn't worry about what side of the relay is 85 or 86. Just know that on a relay with 4 connectors 85 and 86 go to the coil (low current) and 30 and 87 are on the high current side.

You are just scratching the surface on relays with a 4pin one. You may want to search for some online resources that will explain more.
 
TrueTexas said:
The relay can be drawn multiple ways. I wouldn't worry about what side of the relay is 85 or 86. Just know that on a relay with 4 connectors 85 and 86 go to the coil (low current) and 30 and 87 are on the high current side.

You are just scratching the surface on relays with a 4pin one. You may want to search for some online resources that will explain more.
Click to expand...
If the relay has a diode, 85/86 does matter. If the current flows the wrong direction, the diode will short the switch circuit to ground. Think of a diode as a check valve.
 
Steel City 06 said:
If the relay has a diode, 85/86 does matter. If the current flows the wrong direction, the diode will short the switch circuit to ground. Think of a diode as a check valve.
Click to expand...

Yeah. I mentioned that in an earlier post above. OP was asking about whether 85 or 86 being on the left or right of the diagrams made a difference.
 
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Thanks all. I found this, and will read it when I have my hands on the relay again. Sounds like I probably mis-read one of the numbers. Will report back here soon.

In the meantime, I do wonder about question #3: When is it safe to just ground to the frame or tie into another accessory’s ground wire? And when do I need to ground all the way back to the battery’s negative terminal? For instance, the black ground wire on this switch I’m installing.
 
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