morbias Posted January 14, 2011 Share Posted January 14, 2011 (edited) Today I replaced the bulbs in my dash with LEDs, they all work apart from the two that illuminate the tach. If I swap the bulbs back in, the bulbs work fine. As far as I'm aware the illumination lights for the tach are on the same circuit as the rest of the dash lights, so I don't know why they aren't lighting up. Dunno if it's worth mentioning but the tach isn't working, there's an unplugged wire near the coil which I assume is the tach. When it's plugged in to the negative terminal the car won't start, so I left it unplugged. I can't see this having anything to do with the dash lights though. Does anyone know what the problem could be? The car is an early 74 260z. Edited January 14, 2011 by morbias Quote Link to comment Share on other sites More sharing options...
kal7467 Posted January 14, 2011 Share Posted January 14, 2011 some circuits need a certain amount of resistance to work. not sure if this is one of them but if it is you would need to put a resister in line with one of the led's so the car senses a load. if not I am sure someone more knowledgeable will chime in. Quote Link to comment Share on other sites More sharing options...
morbias Posted January 15, 2011 Author Share Posted January 15, 2011 The thing is the other LEDs on the circuit work fine; it's as if the tach has a resistor in line to the LEDs causing them not to light. I'm thinking I might just give up and get a couple of green bulbs for the tach. Quote Link to comment Share on other sites More sharing options...
LanceVance Posted January 15, 2011 Share Posted January 15, 2011 Try wiring your LEDs with the stock bulbs in line with them. If they work then, then you need a resistor. Quote Link to comment Share on other sites More sharing options...
morbias Posted January 15, 2011 Author Share Posted January 15, 2011 (edited) Well without taking the dash apart and soldering new connections I can't do that, and really I'm not that bothered but I still don't see why the other LEDs in the dash work because they are all on the same circuit (unless I am mistaken?) Edited January 15, 2011 by morbias Quote Link to comment Share on other sites More sharing options...
kal7467 Posted January 15, 2011 Share Posted January 15, 2011 do the others work without any bulbs in the tach? if not than all the lights are prob on the same circuit and the circuit as a whole needs some resistance in it Quote Link to comment Share on other sites More sharing options...
morbias Posted January 15, 2011 Author Share Posted January 15, 2011 Yes, the other lights work with no bulbs in the tach, according to the FSM they are wired in parallel which is why I have no clue why they don't work Quote Link to comment Share on other sites More sharing options...
bjhines Posted January 15, 2011 Share Posted January 15, 2011 grrrrr. Light Emitting DIODE. You have them in backwards. Operational characteristics of a Diode is the KEY to your problem Quote Link to comment Share on other sites More sharing options...
morbias Posted January 15, 2011 Author Share Posted January 15, 2011 (edited) You can't put them in backwards, they are the bulb type. EDIT: like this ...unless for some weird reason the sockets have been wired back to front on the tach and not the other dials. I'll have a look tomorrow when the sun comes out. Edited January 15, 2011 by morbias Quote Link to comment Share on other sites More sharing options...
kal7467 Posted January 16, 2011 Share Posted January 16, 2011 are LED's really something to grrrr about... Quote Link to comment Share on other sites More sharing options...
morbias Posted January 16, 2011 Author Share Posted January 16, 2011 Problem solved, the sockets for the tach bulbs were wired backwards; I took apart the LED units for the tach and reversed the polarity, then soldered them up again. Worked a treat! Thanks for the imput guys Quote Link to comment Share on other sites More sharing options...
LanceVance Posted January 16, 2011 Share Posted January 16, 2011 Was it improperly wired from the factory, or had the dash wire harness been worked on before? My dash is out right no so I might do this, but I never want to have to take it out once it goes back in. Were they all the same bulb type? Part #? Glad you got it worked out, good call on bjhine's part! Quote Link to comment Share on other sites More sharing options...
morbias Posted January 16, 2011 Author Share Posted January 16, 2011 I've no idea if it came like this from the factory or not, the weird thing is the wire colour codes were correct (as in; wired identically to the other dash bulb sockets). The LEDs I used were these: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260320180937&ssPageName=STRK:MEWNX:IT They needed filing down so they would fit in the bulb housings, here's how much I needed to take off: This is one of the two LED bulbs I had to take apart to reverse for the tach: pretty easy to do, only took 10 minutes to do both. The dials look really good in green, I couldn't get a picture because the camera on my phone is useless in the dark. Quote Link to comment Share on other sites More sharing options...
bjhines Posted January 17, 2011 Share Posted January 17, 2011 (edited) The Grrrr was for the ignorance of electricity. I am glad the situation is solved. If you don't know the answer then don't type a bunch of bullshit. I know where you got the "need resistors with LEDs" crap and it does not apply, does the word "Thermal flasher" mean anything when talking about dash lights? You guys are going to find a lot of issues when you go changing incandescents to LEDs. LEDs are not at all like light bulbs. If you want to dim the dash LEDs then you will need to replace the dimmer potentiometer with a variable duty cycle PWM circuit. That can be built with $10 worth of radio shack parts and it works like a champ... unless you still have a few incandescents in the circuit and you fry the output devices. problems problems problems. If your tach is not working then someone has changed your ignition/coil circuit(ignorantly bypassed the ballast resistor). I am willing to bet your tach DOES WORK when your key is in the START position. You need to trace the wires according to the factory diagram and hook them up correctly. The tachometer is in series with the coil with a ballast resistor bypass in the start-key position. The factory tach and ignition circuit is sketchy and could use a more modern approach. Bypassing the ballast resistor can allow the start position to back-feed all of the ignition related circuits through much smaller gauge wires. This is not a problem when used intermitantly, but there are quite a few ways this can bite you in the ass. Edited January 17, 2011 by bjhines Quote Link to comment Share on other sites More sharing options...
LanceVance Posted January 17, 2011 Share Posted January 17, 2011 You guys are going to find a lot of issues when you go changing incandescents to LEDs. LEDs are not at all like light bulbs. If you want to dim the dash LEDs then you will need to replace the dimmer potentiometer with a variable duty cycle PWM circuit. That can be built with $10 worth of radio shack parts and it works like a champ... unless you still have a few incandescents in the circuit and you fry the output devices. problems problems problems. So lets assume there are no incandescent bulbs left in the entire circuit you wish to have dimming capabilities with. what exactly do you recomend to the avererage joe-schmoe who doesn't know what he's looking at when he goes to radio shacks parts bin? I'm sure I could spend $100 and still not get the correct components. Please forgive my ignorance of electronics, but I could google "variable duty cycle PWM circuit" till the cows come home and would probably end up just like the OP with misguided or outright wrong assumptions about what I'm doing. The spirit of this forum is to create a collective of information, not put down people who don't know any better. Why not put up the information if you care to share it rather than just doom this thread to the shed? Maybe if we answered the majority of these questions here it wont come up again, and you can direct your "grrrs!" elsewhere. I don't mean to be confrontational if its coming off that way, but this is something I'm also interested in doing, and like the OP only have a limited (call it near non-existant) working knowledge of electric components. Or would you prefer more BS be posted to misguide the next guy? Quote Link to comment Share on other sites More sharing options...
morbias Posted January 17, 2011 Author Share Posted January 17, 2011 (edited) I have to agree, you don't have to assume everyone is ignorant of the facts. Just for the record I do know how a diode works, about pulse width modulation (though the rheostat is bypassed as I don't care about the dimming function), and electronic vs thermal flashers (I'm doing my turn signals too). The sockets on the tach being wired up back to front wasn't exactly the most obvious thing especially since the colour coding was essentially correct. I thank you for the advice but I'm sure you could be a little less condescending And yes, the engine electrics are a mess, I haven't had time to look at them yet. Looks like I'll have to unwrap the whole engine harness though as the wires aren't colour coded as per the FSM EDIT: The ballast resistor was bypassed as you suggested, I unwrapped the harness and wired it all up correctly (the FSM was wrong and had the wrong wire colours!) and now the tach is working perfectly, so thanks again Edited January 17, 2011 by morbias 1 Quote Link to comment Share on other sites More sharing options...
bjhines Posted January 17, 2011 Share Posted January 17, 2011 (edited) This is not Zcar.com and I was referring to the new member who brings up "need resistors". Morbias, You have posted questions, pictures, and results. This is EXACTLY what we want to provide on this forum. Thank you very much for this post, as it may provide someone else with help in the future. We try to keep the fluffery out of the posts. There are plenty of folks who know how things work and post real answers. The PWM circuit can be purchased from a variety of sources or built using a 555 timer chip. I will spend a little time and see what I can find for you guys to purchase rather than DIY. I'll get back to this. Edited January 17, 2011 by bjhines Quote Link to comment Share on other sites More sharing options...
morbias Posted January 17, 2011 Author Share Posted January 17, 2011 There are some easy to use pre-built PWM controllers on ebay if anyone is interested: PWM controller Quote Link to comment Share on other sites More sharing options...
bjhines Posted January 17, 2011 Share Posted January 17, 2011 Morbias, That is a great choice, except you might want to divorce the pot for mounting purposes. You can get an appropriate value, long-shaft pot at Radioshack and cut it to length. The on-off switch is redundant. Quote Link to comment Share on other sites More sharing options...
Pharaohabq Posted January 20, 2011 Share Posted January 20, 2011 Hmm I'd always thought LED's should be connected with a series inline resistor just to limit current should there be a short. It's been years since my electronics classes but a small resistor with each LED shouldn't affect your brightness, but could save your harness since when a Diode has flowing current, there's hardly any resistance so the amperage could draw up pretty high in comparison to incandescent bulbs, the resistors could prevent this. I dunno though, my info is 20+ years ago memory so it's entirely possible I'm wrong. Hey I like those LED bulbs though. The PWM unit. Nobody explained how that works with LED's. Basically an LED is like a switch either it's on or it's off, the Pulse Width Modulation (PWM) box makes it so you're flipping that switch on and off really fast. So that on bright, the LED is pulsed longer to an always on condition. As you turn the POT down, the pulses actually get shorter so the LED appears to Dim since the time that they're actually on is less. This flashing on/off is still happening so fast you can hardly see, like a TV, so to our eyes it just looks brighter or dimmer. This won't hurt your car so long as it's only in the dash circuit. Pulsed power probably wouldn't be good for the ECU on a newer Z. Phar Quote Link to comment Share on other sites More sharing options...
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