Tachometer illumination issue [Solved]

[Oblithian]

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.

**So I finally uploaded how I dealt with this:

 

Edited January 2, 2021 by Oblithian
Additional Detail, and noting that it is solved (in the title, so it is more helpful).

[jhm]

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.

[jsmsmk]

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

[morbias]

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. 

[Oblithian]

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 July 23, 2018 by Oblithian

[philbu]

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. : )

Edited September 16, 2018 by philbu

[philbu]

Problem solved, switched wires and LEDs now work in the tachometer  : )

[Oblithian]

Glad my confusion has helped someone.

[Goose280Z ‘78]

On 6/16/2020 at 9:38 PM, Oblithian said:

Glad my confusion has helped someone.

Oblithian - A Great Big THANK YOU for taking the time back in July 2018 to solve what looks like one of the biggest mysteries of the Z LED issues.  I just purchased a ‘78 280Z a couple of weeks ago and am getting the wiring all squared away while tackling the instrument lighting.  The car itself is in Great shape both inside and out, however the old fuse block is corroded and has 3 fuse holders with a prong missing.  I have ordered a new Blade Fuse block (Rear Terminal ATC ATO Fuse Block Bussmann 15712-14-06-21A) and will replace over the old glass fuse block in the coming days.

 

Question: Did you find the need to replace the Rheostat Dimmer Switch With a PWM switch due to the LED’s or not necessary?

 

Question: My HAZZARD switch may either be shorted or simply “gone bad” - when I press the hazzard switch it immediately makes my voltage meter in the dash go to 0.  It takes some time but then the voltage meter resets once I turn off and then renegade the electrical by turning the key.  However, sometimes the HAZZARD switch actually works.  Any Thoguhts?

 

If I need to get a new hazzard switch, do you have any ideas where I might be able to find one?  Google searches are coming up BLANK for OEM switches.

 

Thanks!!!!!!!!!!!!

[Oblithian]

No I just left the stock dimmer, I thought about installing an adapter but the LEDs I went with aren't bright enough to need to be turned down (I may buy brighter ones, but they're at least bright as the stock bulbs with the green lenses).

The hazard sounds like there is a short, apparently it is common to get one in the indicator sockets? So I would check them first but a short could be anywhere really... I mean, if you already need a fuseblock maybe check again after that's replaced.

Best bet for a stock switch is some of the local datsun clubs, some people just have stacks of parts.

[Goose280Z ‘78]

Thanks again for the info.  I’ll be installing 2 Blue Sea (5035) Blade Fuse blocks - 1 for the 24 hour side and one for the accessories/switch side. I’ll add an in-line fuse for the radio for the 7th (13th) fuse on the accessory side.  The ability to use “jumper terminals will allow me to mimic the original fuse layout perfectly. There’s a good video on YouTube which seems to make it fairly simple.

[Goose280Z ‘78]

Forgot to mention the Dash LEDs.  I went with Ice Blue and they are plenty bring, and the stock dimmer tones them down a bit if wanted, however, they aren’t bothersome on high so I’ll skip installing the PWM switch. (I was just wondering if it was necessary).  We’ll see how the Hazzard’s work once the new fuse blocks are in.  The original block is rusted, corroded and 3 have only 3 prongs.

[ETI2K]

@Goose280Z '78 - Congratulations.  Your car looks to be in great shape.  Here's to no surprises 🍻