Tach gauge indicator lights dead?

[chaseincats]

Hi guys,

Odd question for you.

One of my tach illumination lights died (the other 4 still work).  A week later, the left indicator dash tach light died, and today the right one died (the front & rear exterior indicator lights all work however).  I tried to remove the tach but 90 minutes later I couldn't get it out (on account of the dash cap's lip that surrounds the gauge.

I also was able to unplug the 2 general light connectors behind the dash after a bunch of fiddling hoping to see some corrosion, but they look brand new.  I also took a look at the bulbs, and they aren't burned out.

Anyone have any other ideas?

 

-chase

[Zed Head]

Check for voltage at the plugs if you're not sure (I love my multimeter).

Check the ground circuit from the bulb mount metal to body ground.  Can't remember if those bulbs use a single electrode and a mounting ground or if they are two electrode, with a ground wire.  Grounds are the hidden circuit killer in the old Z's.

And, if you replaced the bulbs recently, some of the new bulbs from the big aftermarket guys are actually too big to fit.  They'll go in but then work loose over time.

On the dash cap, if you have some Mylar sheet, like for making transparencies, you can slide it between the gauge edge and the cap edge to make a ramp to slide the gauge out.  Add a little lubricant of some kind to help.  Armor All, for example.

[chaseincats]

49 minutes ago, Zed Head said:

Check for voltage at the plugs if you're not sure (I love my multimeter).

Check the ground circuit from the bulb mount metal to body ground.  Can't remember if those bulbs use a single electrode and a mounting ground or if they are two electrode, with a ground wire.  Grounds are the hidden circuit killer in the old Z's.

And, if you replaced the bulbs recently, some of the new bulbs from the big aftermarket guys are actually too big to fit.  They'll go in but then work loose over time.

On the dash cap, if you have some Mylar sheet, like for making transparencies, you can slide it between the gauge edge and the cap edge to make a ramp to slide the gauge out.  Add a little lubricant of some kind to help.  Armor All, for example.

Update for you: I was wrong about a burned out tach light - the bulbs are just too dim to illuminate the area where the redline+ bit is.  The turn signal lights still aren't working however.

I ended up using a test light to verify that I am indeed getting a light pulse to the harness connector for the signals and I am.  I did some research online and found out that the indicator lights (unlike the illumination lights) are indeed 1 wire and not 2.  So I'm guessing that means they aren't grounding properly to the housing (or the housing's ground is missing, right)? 

 

Update: Got the lights working.  For those who have the same issue, the tach grounds to the body via the tach mount screw on the underside of the dash.  Sand it down a bit and crank that screw and that should fix your grounding issue.

Edited August 29, 2020 by chaseincats

[SteveJ]

7 minutes ago, chaseincats said:

Update for you: I was wrong about a burned out tach light - the bulbs are just too dim to illuminate the area where the redline+ bit is.  The turn signal lights still aren't working however.

I ended up using a test light to verify that I am indeed getting a light pulse to the harness connector for the signals and I am.  I did some research online and found out that the indicator lights (unlike the illumination lights) are indeed 1 wire and not 2.  So I'm guessing that means they aren't grounding properly to the housing (or the housing's ground is missing, right)? 

I suggest you modify your research to look at the factory wiring diagram. The turn signal sockets are NOT grounded on the meter body. There is a ground wire in the connector. The ground is common for the tachometer itself and the turn signals.

Both the GB and GR wires come off the C-5 connector.

[chaseincats]

On my tach

1 minute ago, SteveJ said:

I suggest you modify your research to look at the factory wiring diagram. The turn signal sockets are NOT grounded on the meter body. There is a ground wire in the connector. The ground is common for the tachometer itself and the turn signals.

Both the GB and GR wires come off the C-5 connector.

On my tach, the turn signal wires are single wires (BW).  The gauge illumination lights have 2 wires (GB/GR)

[SteveJ]

That is for a 240Z. Your signature says you have a 280Z.

[chaseincats]

10 minutes ago, SteveJ said:

That is for a 240Z. Your signature says you have a 280Z.

I have a 280z.  If that's the case, then maybe somebody put a 240 tach in it?

Either way, on mine, the indicator lights only had one BW wire each and once I cleaned the mounting bracket and bolted the housing down, they worked.

Edited August 29, 2020 by chaseincats

[SteveJ]

It is doubtful someone used a 240Z tach in your car unless the wiring was modified. Until you post photos of your tach with the light sockets and connector, I am going to stick by what the factory wiring diagram says about your car. The wiring diagrams the same for the 260Z through 280Z for the tachometer. I know the tachometer in my 260Z was wired per the factory wiring diagram. 

[SteveJ]

I stand corrected. I found a picture on this site for the turn signals on a 280Z tachometer.

 

[Zed Head]

There's a rheostat in there somewhere.  This is from the 78 FSM, 

[Zed Head]

Turning...

[chaseincats]

My rheostat works but I've always wanted to bypass it to see if the lights get any brighter because who knows how much/if its corroded on the inside.