Tail Lamp Sensor Operation

[Mushatsu]

So, I've been doing some research into tail lights for a 91 N/A and have come across some conflicting information on the operation of the Tail Lamp Sensor. I personally don't own a Z, and the last one that I worked on was a 280Z, but I'm trying to help a friend make some LED tail lights (don’t judge ).

Apparently, there are three schools of thought on tail lamp sensing; monitoring voltage, current, or resistance.

Because, resistance would have to be checked without power on the circuit, the light should come on when the check is made and probably stay on until the check is made again. I'd say on a power cycle basis, as you probably will be turning off the car to change the bulb. Also, this would allow for a change bulb soon message, as resistance of a bulb goes up as it begins to fail. So, because (from what I can gather) the light only illuminates when the circuit is on, I'd be willing to guess that this isn't the system used.

Monitoring voltage could be done by measuring voltage after the bulb. There should be enough resistance in the ground side of the circuit to see a measureable voltage (milli-volts would work). No voltage means a bad bulb. If this is the system used, I wouldn't see why using aftermarket bulbs would be a problem, as there is either voltage or there isn't. I realize that by utilizing different bulbs that resistance of the circuit is changed. This should change the current and the voltage at different points in the system. Again, I'm guessing that this isn't the system used, mostly from the apparent sensitivity (again, hearsay) of the system.

With the current method, the unit would just be an ammeter. If current gets too low trigger the light. This could be greatly affected by inline resistance and by aftermarket incandescent bulbs (8 bulbs in parallel, and having to see the current change of 1 going out). This system would also make the brake lights fail off (bad idea). Unfortunately, this would have to be the system I'd choose if not using a computer module to check the system. It is quick and easy.

But, I have never worked with this system in this car. So, could anyone confirm what the real method is? And if possible, could I get a pin out for the module or a picture of the inside or a wiring diagram.

I realize that there will be responses like “Voltage, because when I press on the break I get voltage at the bulb”. Obviously, this can’t be the way because the circuit will always get voltage barring a problem before the bulb. I don’t want to sound like some sort of noobie jerk, but I get tired of know-it-all blowhards that don’t know anything and haven’t had the chance to see who is really knowledgeable.

Thanks for the help.

[Ace2cool]

Hmmm, to my knowledge, the current is not monitored, as there is always current present if there is a changed voltage/resistance. I would actually love to dig into a schematic of the voltage regulator/sensor, but haven't found one. The closest thing I came across was a complete wiring diagram that someone posted up here ages ago, and I wouldn't know where to even begin looking for that. Therefore, I can only speculate as to how it works, but I believe I have a decent understanding from my experience with the tails.

I believe the way it operates is by measuring how many volts are dropped from each individual tail light bulb, and by comparing the input/output voltage of each individual bulb, determine the resistance of the bulb, and if it measures out of spec, throw an indicator light to the dash. As you stated, when a bulb burns out, the resistance goes up and up until it becomes infinite. That would indicate bulb failure.

However, if resistance drops, that indicates to the sensor that there is a short either in the wiring somewhere between the sensor and the bulb or IN the bulb itself, also indicating failure, since insufficient volts were dropped to power the bulb. As we all know, LED bulbs have much lower power requirements than traditional incandescent bulbs, since they produce less heat. Therefore, the sensor reads the lower dropped voltage on the LED's as a short.

The easiest and simplest solution, IMO, would be to test the dropped voltage on both the low and high circuits on the incandescent bulbs and use resistors to try and emulate the same dropped voltage from each. May I inquire as to the design of said LED taillights? Will they be simple "bulb" replacements or a full LED board? The bulb replacements would be easier to simulate dropped voltage on, seeing as you could deal with each "bulb" separately.

But I do believe that if you get the applied voltage and the resistance correct, the current will be within specs as well. It's been a long time since I've been through electronics school though.

So even if it does monitor current, as long as input voltage and resistance are within operating specs, the output voltage and total circuit current SHOULD be within specs.

Hope this helped. Sorry for the long response, but that's about as simple as I can think when it comes to electronics. Let us know if you find anything out.

[Mushatsu]

I would actually love to dig into a schematic of the voltage regulator/sensor, but haven't found one. The closest thing I came across was a complete wiring diagram that someone posted up here ages ago, and I wouldn't know where to even begin looking for that. Therefore, I can only speculate as to how it works, but I believe I have a decent understanding from my experience with the tails.

I've looked at a complete vehicle wiring diagram, http://www.300zx-twinturbo.com/cgi-bin/manual.cgi, and it looks like the sensor has about 8 inputs. Sounds like a bunch of wires, but I've never seen the sensor.

I believe the way it operates is by measuring how many volts are dropped from each individual tail light bulb, and by comparing the input/output voltage of each individual bulb, determine the resistance of the bulb, and if it measures out of spec, throw an indicator light to the dash. As you stated, when a bulb burns out, the resistance goes up and up until it becomes infinite. That would indicate bulb failure.

However, if resistance drops, that indicates to the sensor that there is a short either in the wiring somewhere between the sensor and the bulb or IN the bulb itself, also indicating failure, since insufficient volts were dropped to power the bulb. As we all know, LED bulbs have much lower power requirements than traditional incandescent bulbs, since they produce less heat. Therefore, the sensor reads the lower dropped voltage on the LED's as a short.

I don't want to seem like I'm being critical, but... When measuring resistance, you cannot have power on the circuit. Seeing as the lights appear to be in parallel, input voltage is the same across all lights, so voltage drop would be the same weather or not a light was there. The only reason that I referenced this case in my initial post was to entertain the theory. I think in practice that this may be a bad idea, because as long as there is a complete circuit the light would remain off. So, the issues with corroded bulbs and improper resistance bulbs shouldn't occure.

So correct me if I'm wrong, but the bulb out light only comes on when the break or tail light is on. So, this should automatically rule out resistance. Also, making an assumption that most circuit designers use on higher voltage low current circuits, wire resistance and such should be zero. This kinda rules out the voltage. I did like the voltage drop idea from above, but if the lights were wired so this would work, it would be all or nothing.

I believe that I may have answered my own question, but I'm still at a loss for the actual case. The wiring diagrams only seem to show the sensor in RH drive models.

As far as the circuit itself, it is true that if resistance and voltage remain the same as the original circuit that current would have to remain the same. V=I*R.

The easiest and simplest solution, IMO, would be to test the dropped voltage on both the low and high circuits on the incandescent bulbs and use resistors to try and emulate the same dropped voltage from each. May I inquire as to the design of said LED taillights? Will they be simple "bulb" replacements or a full LED board? The bulb replacements would be easier to simulate dropped voltage on, seeing as you could deal with each "bulb" separately.

Currently I'm entertaining the idea of designing full drop in boards. I'm hoping to be able to fit the board between the reflector and diffuser. Granted, I have absolutely no idea how the diffuser is held in, so design modifications will be hit and miss.

With the full board, I plan on adding pigtails and a connector to utilize the stock harness. This is for ease of removal/install, and should have the added benifet of making it easy to reproduce if others are interested.

Personally, I don't like the stock layout, so I have modified it a little bit. Here is a proposed layout.The blinker will make the bottom lights blink high/off unless the brake light is on then will blink low/high. This will make more lights on during braking and at night, hopefully increasing safety and coolness.

I've been using PSpice to design the circuit, and am working out some of the bugs. The major one that I am currently facing is will I have to use a constant current driver to push the LED's or will I be able to use a voltage driven system. I am worried that the voltage swing (10v-16v) may not allow the LED's to operate properly. Either the voltage will be too high and the LED's will go poof, or the voltage will be too low and the LED's will not light. Then there is the issue of having the high and low states. More than likely, I'll resort to doing the controlled current setup. It's really not that big of a deal, will result in a more even light output across voltage levels, and will keep the LED's safe from voltage spikes and such. Keeping it all cool could be another issue. Contrary to popular belief, LED's do generate heat. They are only about 20% efficient (vs. 2% for an incandescent). Between 90 or so LED's and a good deal of circuitry, I may not be able to do a stock drop in.

Any comments or suggestions will be taken into consideration. While I've been working on the electrical side and can do the electrical modeling, I (or my friend) don't have the funds. He gave me his old set of stock lenses (he bought J spec lenses) but I haven't had the chance to dissassemble them. This will be an extremely slow work in progress, as I don't plan on doing anything physical until I get a circuit designed. Then there will be a prototype and a final design. The end goal is to have a circuit board printed made then all I have to do is solder on parts.

[Mushatsu]

Now that I can see the picture, it doesn't quite look as good as the original on my computer. But if you look carefully, there is a difference between low and high.

[Ace2cool]

Hm, you make some very good points. I was approaching the matter from a completely different angle, however. I was approaching from a bulb replacement standpoint. What you may consider is just "deleting" the voltage regulator entirely, since you are changing how the tails operate as well. Someone correct me if I'm wrong, but the regulator unit is what sends the signal for the dash indicator light. As long as there is power supplied and a ground, theoretically you should be able to bypass everything completely. Might not be "plug and play", per se, but you could sell a conversion plug specifically for your tails that would take the place of the voltage sensor if you do plan on making these for the public. That would require more extensive wire tracing, however, but is not completely out of the question, IMO.

I would definitely look to the current controlled system, since you seem confident that you can set it up, and like you said, it will protect them from voltage spikes, though unless you're running a high power audio system with no capacitor, I wouldn't be worried about TOO MUCH *knocks on wood*.

I am interested in how you would plan on cooling the circuit board, though.

As far as the circuit itself, it is true that if resistance and voltage remain the same as the original circuit that current would have to remain the same. V=I*R.

That's what I was basically trying to say in a more roundabout way in my first post, but seeing as you're going to attempt a completely different setup as far as operating, I'm not sure how you would go about maintaining the same voltages with different operation. That's past my area of expertise, haha.

As far as how the diffuser is held in, Check the DIY Jspec tails article on how to take the tails apart and remove the diffuser.

http://www.nicoclub.com/articles.php?id=399346

Seems to me they just pop in/out. It's never really that simple though, but that will give you the general idea.

Sorry for the confusion in my original post. We were viewing the issue from two completely different viewpoints, haha. Definitely keep us posted on the progress though!

[Mushatsu]

Building a constant current driver is fairly simple and will provide the LED with the proper voltage at the proper current. I may be over reacting about the heat generation. If I use a fairly focused LED, say 30 degrees, I should be able to generate much much more light with minimal current, like 300 ma per string of LEDs. Using a step up driver to increase the voltage, I could run a setup where very little heat should be generated, just by appropriately choosing the input and output voltage and current. The only circuit that it would matter on is the tail light circuit. Otherwise, how long is the break going to be applied (max I could guess is 10 min). I'll continue working on the circuit and will post some schematics.

As far as the voltage spikes I am refering to is from differences in possible battery voltage (10v) and possible alternator voltage (16v). This may be too large of a gap to make a useable circuit. Probably a bad choice in words. But if voltage is too low the LED won't light. If it's too high, poof. Though a step down circuit would allow me to wire everything in parallel.

Either way, I'm guessing the I'm going to be pulling about 5 amps total, so quite a bit less than stock. If the stock housing can take the heat now, I know it will survive. Cooling will only be necessary if the electrical parts need it.

I'll probably just make some sort of bypass for the lamp sensor. Looks to be like a series of jumpers would work inside of a broken sensor. I'm really trying hard not to cut any factory wiring.

Does anybody out there have a broken tail lamp sensor in the DWF area?

[Sgt]

I didn't take the time to read everything, as I gotta get to work here, so excuse me if I say anything not relevant here.

If the brake and tail light sensor is causing you issues here, you can just delete it. I had a ton of issues with it, so I figured how to completely remove the thing.

If you want to know how. Just let me know and I'll draw up some diagrams.

[Mushatsu]

From wiring diagrams, I figure the easiest way to disable to sensor is to cut the signal wire to the dash light. I didn't look too hard at that part of the circuit, but it either provides power or ground. Because I don't actually own a 300ZX, I really don't know where any in-line connectors are located. Right now the friend that has one is in Florida and won't be back until summer. So, I'll probably just work on the prototype and leave long leads and deal with the sensor later. Removing it could be considered weight reduction right?

[Sgt]

I actually figured out what wires to jump at the tail light sensor to delete it safely. Reason I did that, rather than cutting the signal wire is for fire prevention reasons haha. My brake and tail light sensor, got so hot it started popping resistors.

I started putting higher wattage resistors in and they held for the first few months, but after that, they lasted a few days and kept blowing, so I got fed up and just deleted it properly.

[Mushatsu]

In that case, I'd love to see pictures. My hope is that jumping the sensor will be easier than finding some connector up the line. Then all I have to do is match the connector at the housing.

[raeshaw0699]

I didn't take the time to read everything, as I gotta get to work here, so excuse me if I say anything not relevant here.

If the brake and tail light sensor is causing you issues here, you can just delete it. I had a ton of issues with it, so I figured how to completely remove the thing.

If you want to know how. Just let me know and I'll draw up some diagrams.

An interesting post -

I have problems with my tail lights not working - all other lights, brake indicator and reverse are fine. Would it be possible for you to provide the details of the tail light sensor bypass -
Thanks

[flyerr22]

I have exactly the same issue as raeshaw0699 and would appreciate knowing the deatils for bypassing the sensor as it did not provide any warning of the light failure and seems to be the cause of more problems than its supposed to solve.
Thanks - Steve

[flyerr22]

I have taken out the sensor altogether - to do this I have jumpered 4 & 5 together (Brake lights) and 2 to 7 and 8 (7 for right side tail lights and 8 for left side tail lights) - All lights work as they should I shall now see if this works long term. My only other observation would be that my fogs have been wired into 7 so they work fine, others may need to check that where theirs are wired into. Hope this helps.