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Dash Gauge Illumination Problem


tamo3

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Hi,

 

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

I checked with individual gauge, it works fine.

post-24248-0-03404300-1421371595_thumb.j

 

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

post-24248-0-82256300-1421371560_thumb.j

 

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

post-24248-0-06194700-1421371573_thumb.j

 

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

Fused is checked.

Shunt fuse is checked.

post-24248-0-03159700-1421371824_thumb.j

 

Bypass register near the speed meter gauge.

post-24248-0-29907500-1421371759_thumb.j

 

Brake light, high beam can turn on.

Heater, wiper is working.

 

what else should I do?

 

Thanks,

tamo3

post-24248-0-67406700-1421371899_thumb.j

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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.

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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....

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Thanks for your advice, SteveJ.

 

So, I start testing wire with voltage meter.

post-24248-0-10583000-1421430259_thumb.j

 

What voltage should I expect for this?

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

 

Thanks in advance,

tamo3

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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.

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Checking fusebox. No melt down, no issue found.

post-24248-0-61521900-1421781683_thumb.jpost-24248-0-71397600-1421781689_thumb.j

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.

post-24248-0-37762700-1421782287_thumb.j

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

 

Testing connection one by one.

post-24248-0-98981900-1421782128_thumb.jpost-24248-0-05284100-1421782151_thumb.j

Can't figure out what is the expected behavior.

 

Clean up body ground earth point.

post-24248-0-63836800-1421782196_thumb.jpost-24248-0-61426500-1421782203_thumb.j

 

Replace battery too.

 

I found one mistake on the tachometer wiring.

post-24248-0-62986300-1421782391_thumb.jpost-24248-0-93449500-1421782419_thumb.jpost-24248-0-17074100-1421782427_thumb.j

 

Sealed with the heat tube.

post-24248-0-63291800-1421782436_thumb.j

 

 

 

 

then...

 

post-24248-0-68320600-1421782517_thumb.j

Works!!!!

 

Thanks for your advice! Solve the problem!

 

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