McMuttley Posted April 5, 2015 Report Share Posted April 5, 2015 (edited) Is there an easy way ? As its raining again (why did I take the hard top off !) thought I would have a go at inserting my LED dash bulbs today. Feeling behind the dash all I can feel is wires and holding brackets, no obvious bulb holders ? Internet pics don't seem to show anything? Do you have to take the small gauges apart to change bulbs ? - eeek ? I am assuming that for the central cluster I can undo the wing nuts and pull the panel fwd for access (although I recall there was little spare wire on any gauges to allow much movement). Is it possible to replace the speedo and taco bulbs in situ? Good news, my dodgy fuel gauge is now working - the needle now flickers to the beat as my radio plays !!!!! ps, if earthing my fog/spot switch near the dash, does it matter what I earth to - dash panel, retaining brackets, or take the earth wires through into the engine bay ? ps, on a pull switch how do I know which is feed and which is earth ?? Thanks as always Happy Easter Eat Chocolate pps - my speedo doesnt have the bit that pokes out of the bottom to reset the trip counter - are these available or am I stick with the clear pipe ? Edited April 5, 2015 by McMuttley Quote Link to post Share on other sites
EdwinTiben Posted April 5, 2015 Report Share Posted April 5, 2015 (edited) HI, I would suggest you use a relay to switch on the fog/spot You dont want too much current running through old switches. I believe there was a post recentrly about fitting spots and relay. If not using a relay: You should have a live feed on your pullswitch (doesnt matter which side) and on the other contact a wire to your spotlamp and earth the spot. all the bulbs can be replaced in situ. On the speedo and rev there are bulbholders pushed in the back of the gauges. On the midsection there are 2 bulbholders which are pushed into holders of the mid section panel (will look for an image). There are no bulbs in the small gauges. Found: See the 2 holders with the red/white wire Edited April 5, 2015 by EdwinTiben Quote Link to post Share on other sites
MilesA Posted April 5, 2015 Report Share Posted April 5, 2015 Hi Austin If you are replacing the ignition light bulb and use an alternator I think you need to incorporate a resistor because of the current difference with an LED. I recall Bob 'Lebroc' mentioning this in the past and no doubt he can confirm / supply details. Miles Quote Link to post Share on other sites
Richardtr3a Posted April 5, 2015 Report Share Posted April 5, 2015 This is a useful thread because I have a problem with one of the dash lights. It has been cleaned and a new bulb fitted.. The holder has been brushed with a wire brush while the heater was out. The lamp works when you push it in at first but you do not get full light when only half way in. So I push it in fully and the lamp goes off. I have checked the wiring and the dash panel has a new earth of it's own. I need an answer to avoid sourcing a lamp holder and worse fitting it. Richard & H Quote Link to post Share on other sites
Lebro Posted April 5, 2015 Report Share Posted April 5, 2015 I found it necessary to ease the centre panel away from the dash to get enough access to the rear. To do this you have to undo & remove the two wing nuts at the bottom, & slacken off the two top wing nuts (do not remove them as they pass through open slots in the dash, & you can slide the centre panel downwards to disengauge. It makes life easier to do this if you remove the speedo first, & through the speedo hole you can undo the oil pressure gauge pipe - which will give you more movement. You will still be limited in movement by the temperature gauge pipe, but there should be a couple of turns in that to give you some flexibility. Bob. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted April 5, 2015 Report Share Posted April 5, 2015 (edited) - Negative earth. set fitted in my instruments http://www.ebay.co.uk/itm/281548480463?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT Peter W PS The pack of 10 costs GBP 3.79 delivered. A real TR uses 6 instrument illumination light bulbs of this style + another 3 for Ignition warning and indicator tell tale and High Beam warning. Edited April 5, 2015 by BlueTR3A-5EKT Quote Link to post Share on other sites
McMuttley Posted April 5, 2015 Author Report Share Posted April 5, 2015 Hi Peter, those is exactly wot i has in mi packet (sadly still not in mi dash !) Quote Link to post Share on other sites
Lebro Posted April 5, 2015 Report Share Posted April 5, 2015 (edited) Yep, they look like the ones I used as well (but mine cost more !) Below photo of resistor mod you may need if you have an alternator fitted, & one showing effect of LED bulbs. I actually then found the lights to be too bright while driving, so replaced my Panel switch with a variable resistor, machining the shaft it to take the original knob. Bob Edited April 5, 2015 by Lebro Quote Link to post Share on other sites
RobH Posted April 5, 2015 Report Share Posted April 5, 2015 Bob, I hope you are not trying to confuse Austin ? The photo is captioned 220 ohm (220R) but the picture shows a 150 ohm fitted. (I expect either value will work). Quote Link to post Share on other sites
BlueTR3A-5EKT Posted April 5, 2015 Report Share Posted April 5, 2015 Bob, It looks like you have the same issue I had with glare/dust in the instrument glasses. I spent some time cleaning the plastic windows and the glass - that removed a lot of the glare issues and most of the dust. I agree they can be a bit bright so I turn them all off. Variable resistor - is that as in heater switch/rheostat - or something more exotic? There are coloured LED available for the more garish look - red would be better to maintain 'night vision' until the muppet with the 4x4 sits on your tail attempting to read what your rear badge might say so he can impress the others at the gym with his sighting. Cheers Peter W Quote Link to post Share on other sites
Lebro Posted April 5, 2015 Report Share Posted April 5, 2015 Rob. Probably trying to confuse myself ! I went through a number of values till I found the highest which worked (probably 220R) but then went down a bit lower to make sure it worked every time. Probably forgot which value I ended up with when I re-captioned the photo. Peter. With the low current of LED's you do not need the power handling of the normal later rheostat. I used a 100R 4W potentiometer. This has an aluminium shaft, which is easily shortened, & machined to mimic the original switch. http://www.ebay.co.uk/itm/24mm-Wirewound-4W-Power-Potentiometer-100-Ohms-/291158093967?pt=LH_DefaultDomain_3&hash=item43ca5ff08f A 75R fixed resistor is used to connect the "lower" pin to ground. see attached diagram. This gives good control over the range of the potentiometer from off, to full brightness. Also you can fit this in the top hole, where as the standard rheostat has to be moved down a hole. Bob Quote Link to post Share on other sites
JohnC Posted July 17, 2021 Report Share Posted July 17, 2021 On 4/6/2015 at 6:51 AM, Lebro said: see attached diagram. Hi Bob, If you still have them, please would you re-post the pics/diagrams for this post? I've fitted LED instrument lights and I'd like to reinstate the dimmer switch. Thanks, John Quote Link to post Share on other sites
Lebro Posted July 17, 2021 Report Share Posted July 17, 2021 (edited) Resistor glued to rear Pot shaft modification half bright full bright off Note, these leds have an internal current limiting resistor fitted. https://www.ebay.co.uk/itm/291470358519?hash=item43dcfcb7f7:g:PrgAAOSwDk5UKRo5 Bob. Edited July 17, 2021 by Lebro Quote Link to post Share on other sites
JohnC Posted August 13, 2021 Report Share Posted August 13, 2021 Thanks @Lebro. I've settled for simply cutting down the pot shaft, and using a little tape around it to make it a tight fit in the original knob. Not as elegant as yours, but does the job. Silly me, when I ordered the pot I didn't order a resistor at the same time, and now all electronics stores are shut. Because, lockdown! So I am yet to finish the job and try it out. Cheers, John Quote Link to post Share on other sites
JohnC Posted August 13, 2021 Report Share Posted August 13, 2021 (edited) On 4/6/2015 at 6:51 AM, Lebro said: Also you can fit this in the top hole, where as the standard rheostat has to be moved down a hole. Hi Bob, What did you mean by this? My dash has only one hole... (or is there more than one on a TR2/3 dash?) Also, reading through the thread and looking at the circuit diagram, I'm confused as to what resistor to use. The diagram and your final comment say 75Ω but elsewhere 220Ω is mentioned, and the photos look like 210Ω. Any final thoughts ? J Edited August 13, 2021 by JohnC Quote Link to post Share on other sites
Lebro Posted August 13, 2021 Report Share Posted August 13, 2021 Hi John, the value of resistor rather depends on the type of LED bulb used, I try different values, until the LED's extinguish just as the control reaches the bottom end of it's travel. Without the resistor they would extinguish a fair way before you got to the end. It all depends on the cut off voltage of the LED's used - they vary. As for the holes, I'm referring to the windscreen wiper / dimmer control holes - sometimes they are swapped. Bob. Quote Link to post Share on other sites
JohnC Posted August 13, 2021 Report Share Posted August 13, 2021 Thanks @Lebro. So the holes reference is irrelevant to my TR6. Phew. In my idle googling, I came across the circuit in the attached image (it came from this thread). I was never any good at electrickery (although your circuit has triggered vague memories of messing with Wheatstone Bridges at school), but it looks like it could be adapted to use the original dimmer by using a suitably rated resistor. Is that right, or am I missing something obvious? Cheers, John Quote Link to post Share on other sites
RobH Posted August 13, 2021 Report Share Posted August 13, 2021 If you really wanted to you could probably make something similar using the original dimmer rheostat and a hefty wirewound for the lower resistor, but I believe the rheostat resistance is around 25 Ohms, so the standing current would be around four times bigger than Bob's circuit as would the heat in the resistors; and surely one reason for the use of LEDs is to prevent that ? I don't think the rheostat has the wiper connection separate so you couldn't replicate Bob's circuit from his July 17th post. Quote Link to post Share on other sites
JohnC Posted August 14, 2021 Report Share Posted August 14, 2021 Fair enough. TBH for me, the reduction in current was a beneficial side effect of switching to LEDs. The primary reason was that I wanted decent dash lighting! I'm now tinkering just because I can I have no idea how an LED bulb is wired internally, so I don't know how the circuit above would work. I'm just curious whether there's a clever way to use the original rheostat by adding external mods. In any case, you're correct that one can't use the original rheostat in Bob's circuit. It's a simple variable resistor, whereas Bob has wired the pot as a variable voltage divider. The original only has a terminal on one end of the resistor wire - the other end floats. FWIW the rheostat in my car (1971 TR6) has a resistance varying from 0.6-5.6Ω. Probably 5Ω with some age. John Quote Link to post Share on other sites
RobH Posted August 14, 2021 Report Share Posted August 14, 2021 (edited) Sorry John - I thought from what you asked that you were contemplating using the rheostat alone. Yes it would be possible to use electronic devices to transform the 0-5 Ohms into a useful control but it would be rather complicated I think. You would need an operational amplifier with a stabilised supply and connected as a voltage follower with gain, plus a medium-power PNP transistor and a handful of other components at the very least. Something like this (or perhaps the other way up using an NPN so the lamps connect to 0V rather than 12V). Changing the pot is so much easier! An LED is just a diode which is connected forward-biassed and which drops something around 2.2 volts. It is a current-fed device and usually requires only a few milliamps to work. There is nothing inside to limit the current so if you just connect it directly to a voltage source it will draw too much current, rapidly overheat and fail. An 'LED bulb' is a lamp made using one or more LEDs with some extra internal component to limit the current and so allow it to be connected directly to a defined voltage like a normal incandescent lamp. That may be done by using something as simple as a series resistor or something as complicated as a chip providing current regulation. The circuit you showed is for a bare LED not an 'LED bulb' and is a bad circuit since at the full travel of the pot the LED is connected straight to supply. The 'designer' mentions that he got away with it because there was some residual resistance in his potentiometer at full travel ! Edited August 15, 2021 by RobH Quote Link to post Share on other sites
JohnC Posted August 14, 2021 Report Share Posted August 14, 2021 Thanks Rob. Lockdown clearly feeds idle and frivolous thoughts . Thanks for the explanation of the circuit. I was aware that LED bulbs have more in them than just several LEDs, but I hadn't appreciated that the circuit was for just an LED alone. Should I delete the image in case somebody as ignorant as I am tries to be clever? I've now installed a pot exactly as per Bob's design (thanks @Lebro). I did run into one wrinkle though. I have a seperate vacuum gauge which has an incandescent 2.2W bulb (65Ω I think). That's enough to upset the balance. Instead of the lights going out just before full travel on the pot, they go out at about 50%. As the vacuum gauge is part of an auxiliary binnacle in top of the dash (mounted in the ashtray hole), I've decided to live with it. I don't leave the binnacle in place all the time, only when tuning (it also has an AFR gauge and knock sensor) so not a big deal. If I wanted to be really anal, I'd source a MES bulb holder and fit an LED bulb. But the LED in the knock sensor is so bright that it would make no difference to glare at night! I do love tinkering John Quote Link to post Share on other sites
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