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Oblithian

Tachometer illumination issue

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1975 280z, I apologize if this is obvious but it's 2 AM and I have been working all day. I just pulled my dash, and replaced all of the gauge bulbs with LEDs. I tested them all, however, upon putting everything back together... The tach's illumination doesn't work (just the tach, and just the illumination, the gauge, signals, high beams, etc. all work). I pulled it twice, tried reconnecting all of the tachometer's connections. I also tried the harness box, and the connections under the steering  column. Where do you guess the issue lies?

(and incase I was unclear, it was working just fine before), I am going to do electrical testing for the dash harness, and the tach. But it may be a while, before I have time again. So please throw your ideas below.

Edited by Oblithian

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I guess the obvious question is do you have 12v and good ground at the bulb socket?  If yes, the bulb is probably bad.  If no, need to troubleshoot that circuit.

 

If you haven't already done so, removing the heater controls center panel makes it easier to work behind the tach.

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On 7/19/2018 at 5:53 PM, jsmsmk said:

When you are installing LED's polarity matters. If you have 12v and ground then check the polarity to the LED.

 

This. I swapped my dash bulbs for leds, pretty sure a couple of the sockets were wired the 'wrong' way around for leds. I ended up pulling the ends off the leds and soldering them back on reversed rather than rewiring the sockets. 

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I located the issue, and forgot to update the post. My apologies.

So the issue was a factory mis-wiring (Apparently Morbias' had the same issue). The green and white (Gw) from the tachometer ran to the red and blue (Rl) on the dash harness. Either the dash side harness was mis-wired, or the tach. An issue one would never discover with incandescent bulbs. So whoever made the mistake, at least it was harmless for 43 years hahaha.

I just undid the two pins and switched them. (Which was easier than pulling the bulbs, let alone soldering them again. I would highly recommend this solution if you ever go to replace your LEDs... 100 years from now)

Problem solved. Thank you for your assistance, even if I didn't end up using it.

Out of curiousity, are anyone else's tachometer connectors mis-wired? ...or is it a mixed bag, where that one guy (we'll call him Doug... Though Toshi is more likely) messed up all the ones he happened to work on, but all of the other employees did it correctly?

Edited by Oblithian

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On 7/23/2018 at 4:28 PM, Oblithian said:

I located the issue, and forgot to update the post. My apologies.

So the issue was a factory mis-wiring (Apparently Morbias' had the same issue). The green and white (Gw) from the tachometer ran to the red and blue (Rl) on the dash harness. Either the dash side harness was mis-wired, or the tach. An issue one would never discover with incandescent bulbs. So whoever made the mistake, at least it was harmless for 43 years hahaha.

I just undid the two pins and switched them. (Which was easier than pulling the bulbs, let alone soldering them again. I would highly recommend this solution as all you need is a small poking device and 2 minutes).

Problem solved. Thank you for your assistance, even if I didn't end up using it.

Out of curiousity, are anyone else's tachometer connectors mis-wired? ...or is it a mixed bag, where that one guy (we'll call him Doug... Though Toshi is more likely) messed up all the ones he happened to work on, but all of the other employees did it correctly?

 

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Hey! Lucky to find this thread (I hope). I have a '78 280z.

I put those smaller leds in the dash and they all worked, but I wanted a little more light, so bought that larger version, installed them, but they did not work in the Tachometer. All others worked fine.

Read Oblithian's post, went out to check and sure enough, the Gw from tach went to Rl pin at harness connection.

Don't know enough about electricity to understand why the lesser led worked ok in tach, but no matter, will switch connector pins tomorrow and hopefully fix the issue. I will confirm here if it works. Thanks! and for newbies, it always pays to do a search first. : )

LEDs.jpg

Edited by philbu

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