Installing a basic relay
03-04-02, 09:45 PM
#1
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Thread Starter
Installing a basic relay
Okay, this is a roughed-over how to on installing a basic automotive relay to turn on any lights using your parking lights as a trigger. Forgive me if I sound rushed or agitated, I wrote this entire thing once and my computer froze so I lost it all!!
So first you'll need to buy a few items: a 5-pin 30-amp automotive relay, an inline fuse holder, a 30-amp fuse, about 20-ft 12-awg wire, a box of t-taps (3 is all you'll need if you don't mess up), roll of electrical tape, and good solid connectors: either use solder or buy male and female disconnects. All of this stuff is available at Radio Shack and should cost you no more than $10-15.
Now you need to get to know the relay. A relay is essentially a mechanical switching device that is activated by a low voltage input to activate a high voltage switch. In this application, your low current trigger will be tapped off the parking lights. Your high current output will be the power supplied to the auxiliary lights by the battery via the relay. The relay itself should be a 1-inch black plastic cube with 5 spades on one face, and some sort of mounting tab on another. The 5 spades are labelled something like 30, 85, 86, 87, 87a (at least these are Bosch's labelling). 30 is your input voltage for the switched device. 87a is an open circuit (no power). 87 is a closed circuit that supplies the high current to your auxiliary lights. 85 and 86 can be interchangeable, but they are the low voltage leads from your parking lights. You can choose either headlights or sidemarker lights. I used the sidemarker lights because the relay can be switched with an input signal as low as 150mV and in case anything went wrong, no big deal.
Hopefully everyone here already knows that every DC electrical device requires to connections: a postive (live) and negative (ground). The colored wire is always ground (yes black is a color) and white is always the live wire. (in AC it's slightly different)
STEP 1
Basically, you first connection is going to be two t-taps off the auxiliary light's positive wire. There is no need to t-tap the negative wire, as the circuit is already well grounded. Now connect the two t-taps you just made with two runs of 12-awg wire, and lead both wires back to the battery pan. Twist the two wires together into one and connect them to the 87 spade.
*The 87a spade will have no connection because it is the open switch.
STEP 2
Next send a wire from the battery's negative post to the 85 spade.
STEP 3
Now make another t-tap off of the positive wire from any parking light, usually the closest one is the best. For instance, tap off the driver-side sidemarker light. Once you've established this t-tap, run another piece of 12-awg wire from the t-tap to 86 spade.
STEP 4
Last is to establish the big power! You will connect the battery's 12v positive post to the 30 spade. BUT before you do that, use that inline fuse holder you bought. It will be a black, plastic, well... "fuse holder", with a looped wire running from one end to the other. Cut the loop into two bare ends. Connect one end to the 12v positive battery post, and connect the other end to the 30 spade on the relay. You may need to splice or crimp extra wire to make the run to the 30 space. It is critical that the fuse holder is very close to the battery. Like less than 12-inches of wire between them both.
STEP 5
Right now the relay system is completely wired up, but there is no fuse in the holder. Therefore no current is running through it so it is still safe. At this point, you'll want to check all connections from and to the relay and once you've determined all is well, insulate it! You want to make the relay water and weatherproof. I did so by wrapping the entire thing in 6 layers of electrical tape. Then tuck or mount the relay somewhere safe. I put mine next to the battery pan which remains relatively dry and cool.
STEP 6
Now you can insert the 30-amp fuse you bought and test out the relay circuit. Turn on the parking lights and in howie's instance, the signal lights will be constant on, and in bizzy's case, the cornering lights will be on always. howie I don't think your signal lights will still blink with this relay configuration unless you located the OEM blinker switch and t-tapped the wire on both sides of that switch then set in two relays on each side. The second relay would detect the blinker signal and use that signal to defeat the primary relay. It's doable, but more complicated. It's only a 20-minute job for an installer, they probably won't charge that much for the trouble.
This whole thing might not make any sense right now because I'm tired from studying all day and am not making any sense myself, but I'll try to make a diagram with pictures soon. My relay is all taped up, wire loomed, and hidden away so I can't show you what I did without destroying it.
So first you'll need to buy a few items: a 5-pin 30-amp automotive relay, an inline fuse holder, a 30-amp fuse, about 20-ft 12-awg wire, a box of t-taps (3 is all you'll need if you don't mess up), roll of electrical tape, and good solid connectors: either use solder or buy male and female disconnects. All of this stuff is available at Radio Shack and should cost you no more than $10-15.
Now you need to get to know the relay. A relay is essentially a mechanical switching device that is activated by a low voltage input to activate a high voltage switch. In this application, your low current trigger will be tapped off the parking lights. Your high current output will be the power supplied to the auxiliary lights by the battery via the relay. The relay itself should be a 1-inch black plastic cube with 5 spades on one face, and some sort of mounting tab on another. The 5 spades are labelled something like 30, 85, 86, 87, 87a (at least these are Bosch's labelling). 30 is your input voltage for the switched device. 87a is an open circuit (no power). 87 is a closed circuit that supplies the high current to your auxiliary lights. 85 and 86 can be interchangeable, but they are the low voltage leads from your parking lights. You can choose either headlights or sidemarker lights. I used the sidemarker lights because the relay can be switched with an input signal as low as 150mV and in case anything went wrong, no big deal.
Hopefully everyone here already knows that every DC electrical device requires to connections: a postive (live) and negative (ground). The colored wire is always ground (yes black is a color) and white is always the live wire. (in AC it's slightly different)
STEP 1
Basically, you first connection is going to be two t-taps off the auxiliary light's positive wire. There is no need to t-tap the negative wire, as the circuit is already well grounded. Now connect the two t-taps you just made with two runs of 12-awg wire, and lead both wires back to the battery pan. Twist the two wires together into one and connect them to the 87 spade.
*The 87a spade will have no connection because it is the open switch.
STEP 2
Next send a wire from the battery's negative post to the 85 spade.
STEP 3
Now make another t-tap off of the positive wire from any parking light, usually the closest one is the best. For instance, tap off the driver-side sidemarker light. Once you've established this t-tap, run another piece of 12-awg wire from the t-tap to 86 spade.
STEP 4
Last is to establish the big power! You will connect the battery's 12v positive post to the 30 spade. BUT before you do that, use that inline fuse holder you bought. It will be a black, plastic, well... "fuse holder", with a looped wire running from one end to the other. Cut the loop into two bare ends. Connect one end to the 12v positive battery post, and connect the other end to the 30 spade on the relay. You may need to splice or crimp extra wire to make the run to the 30 space. It is critical that the fuse holder is very close to the battery. Like less than 12-inches of wire between them both.
STEP 5
Right now the relay system is completely wired up, but there is no fuse in the holder. Therefore no current is running through it so it is still safe. At this point, you'll want to check all connections from and to the relay and once you've determined all is well, insulate it! You want to make the relay water and weatherproof. I did so by wrapping the entire thing in 6 layers of electrical tape. Then tuck or mount the relay somewhere safe. I put mine next to the battery pan which remains relatively dry and cool.
STEP 6
Now you can insert the 30-amp fuse you bought and test out the relay circuit. Turn on the parking lights and in howie's instance, the signal lights will be constant on, and in bizzy's case, the cornering lights will be on always. howie I don't think your signal lights will still blink with this relay configuration unless you located the OEM blinker switch and t-tapped the wire on both sides of that switch then set in two relays on each side. The second relay would detect the blinker signal and use that signal to defeat the primary relay. It's doable, but more complicated. It's only a 20-minute job for an installer, they probably won't charge that much for the trouble.
This whole thing might not make any sense right now because I'm tired from studying all day and am not making any sense myself, but I'll try to make a diagram with pictures soon. My relay is all taped up, wire loomed, and hidden away so I can't show you what I did without destroying it.
03-04-02, 10:22 PM
#3
Lead Lap
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Just one problem
A rather BIG one!
"the circuit is already well grounded"
NOT !!!
Lexus uses negative, ground, switching for ALL of their lights.
The positive side is usually switched, but for a large class, or group, of devices. The way they detect an open bulb, lamp, is they have a small value resister from the plus side of the positive supply (battery) to the load, bulb, and then a relay contact or semiconductor device that provides the ground return for the lamp or bulb.
The output of a amplifier, with the low value resister across its differential inputs, is used to detect current flow when the bulb is supposed to be on, no current flow = open bulb.
"the circuit is already well grounded"
NOT !!!
Lexus uses negative, ground, switching for ALL of their lights.
The positive side is usually switched, but for a large class, or group, of devices. The way they detect an open bulb, lamp, is they have a small value resister from the plus side of the positive supply (battery) to the load, bulb, and then a relay contact or semiconductor device that provides the ground return for the lamp or bulb.
The output of a amplifier, with the low value resister across its differential inputs, is used to detect current flow when the bulb is supposed to be on, no current flow = open bulb.
03-04-02, 10:28 PM
#4
Lead Lap
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But try this...
Let's wire a relay so you must turn the fogs on in the normal manner, with LB, but then they stay on until the parking lights are turned off.
These lamps, fogs and parking, are switched on by grounding the low side through existing relays. You need:
A DPST (double pole single throw) 12 volt relay with 10 Amp contacts.
First, find the low side, "ground" wire, common to both fog lamps.
Open this circuit by cutting this wire where it's common to both fog lamps. Label the end that goes to the fog lamps FL+ and the other end FLR-.
Tie one end of the relay coil to +12 Volts, and the wire end labelled FLR- to the other end of the relay coil. Tie the wire labelled FL+ to a normally open (N.O.) relay contact and tie the opposite end of that relay contact set to ground, the car body.
At this point the fog lamps should operate normally, only on with LBs just the way it came from the factory.
Now find the wire that supplies the low side circuit for the parking lamps. Splice into and attach this wire to the relay's other N.O. contact set. Tie the opposite relay contact of this set to the FLR- and relay coil junction point.
The relay will only energize and the fog lamps come on with the existing fog lamp switch and then the LBs can be turned off and the fogs will remain on since the relay is latched into the energized state by the low side of the parking lamp circuit.
The fog lamps will only turn off if the parking lamps are turned off.
Good luck.
These lamps, fogs and parking, are switched on by grounding the low side through existing relays. You need:
A DPST (double pole single throw) 12 volt relay with 10 Amp contacts.
First, find the low side, "ground" wire, common to both fog lamps.
Open this circuit by cutting this wire where it's common to both fog lamps. Label the end that goes to the fog lamps FL+ and the other end FLR-.
Tie one end of the relay coil to +12 Volts, and the wire end labelled FLR- to the other end of the relay coil. Tie the wire labelled FL+ to a normally open (N.O.) relay contact and tie the opposite end of that relay contact set to ground, the car body.
At this point the fog lamps should operate normally, only on with LBs just the way it came from the factory.
Now find the wire that supplies the low side circuit for the parking lamps. Splice into and attach this wire to the relay's other N.O. contact set. Tie the opposite relay contact of this set to the FLR- and relay coil junction point.
The relay will only energize and the fog lamps come on with the existing fog lamp switch and then the LBs can be turned off and the fogs will remain on since the relay is latched into the energized state by the low side of the parking lamp circuit.
The fog lamps will only turn off if the parking lamps are turned off.
Good luck.
03-04-02, 11:39 PM
#5
Lexus Fanatic
Thread Starter
Re: But try this...
wwest, here was my situation... My car came with both foglights DOA. Despite my efforts, I couldn't isolate the break or short in the system, therefore I just wired a relay over it to bypass the factory wiring. I just now noticed that the foglights don't come on with in the fog lamp switch, even though I tapped the low voltage trigger off the sidemarker light which does turn on! I can only now assume that this is because of Lexus using a negative relay switcher and that somewhere along the line, that relay failed. Yet I still have my foglights using the factory ground and they work fine with the LBs.
I'm not completely clear with the neccessity of the secondary DPST relay. FLR- is the end of the ground not attached to the foglight, therefore it is the end that goes to the ground relay. This ground relay circuit is permanently open as far as I know. But were it to function properly, it would work like so... When the ground relay is closed, the circuit is completed which pulls the DPST relay to an energized state and closes the relay coil, which in turn sends power to the FL+ end of the foglight. But wasn't FL+ the ground? Maybe I'm just tired, but I'm not understanding this circuit?????
I'm not completely clear with the neccessity of the secondary DPST relay. FLR- is the end of the ground not attached to the foglight, therefore it is the end that goes to the ground relay. This ground relay circuit is permanently open as far as I know. But were it to function properly, it would work like so... When the ground relay is closed, the circuit is completed which pulls the DPST relay to an energized state and closes the relay coil, which in turn sends power to the FL+ end of the foglight. But wasn't FL+ the ground? Maybe I'm just tired, but I'm not understanding this circuit?????
03-05-02, 07:58 AM
#6
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relay
The relay coil "+" is supplied with +12 volts "forever".
The relay coil "-" is initially energized by the fog lamp circuit's switched ground.
One set of the relay N.O. contact "set" is used to "latch" the relay in the energized state, one end to parking lamp "-", switched ground, the other end to relay coil "-".
The other relay N.O. contact "set" is used to energize the low, "-" side of the fog lamp circuit.
The relay can only "pick-up" with actual fog lamps being turned on.
Once it is "picked up" it will not drop out until the parking lights are extinguished, manually or automatically.
The relay coil "-" is initially energized by the fog lamp circuit's switched ground.
One set of the relay N.O. contact "set" is used to "latch" the relay in the energized state, one end to parking lamp "-", switched ground, the other end to relay coil "-".
The other relay N.O. contact "set" is used to energize the low, "-" side of the fog lamp circuit.
The relay can only "pick-up" with actual fog lamps being turned on.
Once it is "picked up" it will not drop out until the parking lights are extinguished, manually or automatically.
03-05-02, 12:47 PM
#7
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above post is correct...I used to own an electonics corporation. So, I am very familiar with relays/transistors, etc. It is NOT a good idea to suggest that you can or should hook up your volume VR (varibale resistor) to control your 'hacked' light setup.
I too would like those lights to stay on. But, you must keep in mind that the electrical circuit on our cars is (essentially) a closed loop system and to arbitrarily put that load on a VR that is certainly underated will lead to problems. And could even cause an electrical fire.
Trust me everything in there is rated and related attaching a relay or a VR without knowing the exact OHM's or even pico values will be bad. I'm not saying you can't (err) rig something that will work, seen it done many times. But without truly knowing what extra load your putting on what cicuit (I take it you dont have the schematic) eventually you will be hating your decision....
Flame away.......
I too would like those lights to stay on. But, you must keep in mind that the electrical circuit on our cars is (essentially) a closed loop system and to arbitrarily put that load on a VR that is certainly underated will lead to problems. And could even cause an electrical fire.
Trust me everything in there is rated and related attaching a relay or a VR without knowing the exact OHM's or even pico values will be bad. I'm not saying you can't (err) rig something that will work, seen it done many times. But without truly knowing what extra load your putting on what cicuit (I take it you dont have the schematic) eventually you will be hating your decision....
Flame away.......
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03-05-02, 02:59 PM
#8
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Thread Starter
Okay, this is basically what I have... Keep in mind my foglights didn't work at all prior to this install so whatever you may have recommended as a general relay circuit may not function under my circumstances. Please advise me on what needs to be done in this circuit below...
03-05-02, 03:39 PM
#9
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What?
krypto:
I haven't the foggest notion of what you're writing about.
Vr, variable resister? Where did/does that come in?
But in my case I do have full and complete schematics for 92 LS, 00 GS, 00 RX, and 01 RX.
Complete schematic of the fog lamp relay will be along shortly.
Sorry for the delay, I thought the verbiage would suffice, I didn't realize the schematics would be needed.
I haven't the foggest notion of what you're writing about.
Vr, variable resister? Where did/does that come in?
But in my case I do have full and complete schematics for 92 LS, 00 GS, 00 RX, and 01 RX.
Complete schematic of the fog lamp relay will be along shortly.
Sorry for the delay, I thought the verbiage would suffice, I didn't realize the schematics would be needed.
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