Dash Gauge Illumination Problem

[tamo3]

Hi,

 

I try to replace the illumination light bulb to LED while I finished dash repair.

I checked with individual gauge, it works fine.

 

When I mount dash, the illumination does not turn on.

 

So, I removed dash and connect wiring to start trouble shooting.

 

I unplugged headlight, all the gauges except clock and speed meter.

Fused is checked.

Shunt fuse is checked.

 

Bypass register near the speed meter gauge.

 

Brake light, high beam can turn on.

Heater, wiper is working.

 

what else should I do?

 

Thanks,

tamo3

[SteveJ]

When you checked it out of the dash, did you do it with the dash harness, or did you use another source?

[Zed Head]

Somebody (SteveJ maybe?) has pointed out in the past that LEDs are polarity sensitive.  You only show one LED application, but maybe you replaced a bunch.  Or maybe you tested the speedo with one polarity but got the opposite when you reinstalled.

[SteveJ]

That's what I was thinking, as well.

[tamo3]

Thanks for the quick reply.

I use original harness. When I tested individual gauge, I made sure to connect (+) to 12v and  (-) to ground on the battery terminal.

 

In order to avoid other factor, I replaced LED to orignal light bulb, but no luck so far....

[tamo3]

I don't know whether BA9 has any polarity issue...

https://www.superbrightleds.com/moreinfo/ba9s-ba7s/ba9s-led-bulb-5-led-tower/2077/

[SteveJ]

Yeah, Superbright LEDs tends to market bulbs that aren't polarity dependent. So now you need to start tracking down voltage to see where you're losing the circuit.

[tamo3]

Thanks for your advice, SteveJ.

 

So, I start testing wire with voltage meter.

 

What voltage should I expect for this?

Should I expect same as what voltage of the battery shows?

 

Thanks in advance,

tamo3

[SteveJ]

I just remembered something. If your rheostat is turned some, your LED lights may not come on. D'oh!

 

If your rheostat is turned to all of the way bright then follow the directions below. Stop and investigate for any failures.

 

Disconnect the Combo switch and unplug your gauges from the dash harness.

First, check to make sure you have 12 VDC to ground on the GL wire in the dash harness at the Combo switch.

Next, check for continuity (<1 ohm) between the GL and GW wires on the Combo switch.

After that you can plug in the Combo switch and go to all of the dash harness connectors for the gauges and check for 12VDC to ground at the GW wire.

 

Disconnect the Combo switch again.

Check for continuity (<1 ohm) between the RL wires and ground. If the resistance is high, it may be the rheostat.

[tamo3]

Thanks SteveJ.

 

I bypassed rheostat(register) from the beginning (see photo in the 1st post). 

I will check the method you advised when I get home tonight and post update here : -)

 

Thanks again!

[tamo3]

Checking fusebox. No melt down, no issue found.

Looking at wiring diagram and I found out this 20A fuse run through so many wiring. It abused so much!

 

But just in case, I replaced all of the 40 years old fuses.

I learned that even though it visually looking OK fuse might be broken.

 

Testing connection one by one.

Can't figure out what is the expected behavior.

 

Clean up body ground earth point.

 

Replace battery too.

 

I found one mistake on the tachometer wiring.

 

Sealed with the heat tube.

 

 

 

 

then...

 

Works!!!!

 

Thanks for your advice! Solve the problem!

 

[SteveJ]

So, am I correct in thinking it was a polarity issue with the LED bulb?