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521 Instrument Light upgrade gone horribly wrong...help!


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So, thought it would be cool to install LED lights for my instrument gauge to brighten them up. Read the posts...looked simple enough..right?


Round 1.


During removal of instrument panel from dash I hit the something on removal...

bzzzt....smoke from back of gauge cluster. (guess I should have remembered to

removed the negative on the battery.


No instruments lights. Back to the forum. Burned out patch on circuit board.

Read forum..repaired circuit board with wire and solder.


Round 2:

Reinstall gauge cluster with regular bulbs, battery...lights all work. Remove

cluster to disassemble unit to remove the green bulb housings to get more light.


Round 3:

Got my LED's in.. gauge ready to go. Reinstall unit...BZZZZT! Smoke..again! My negative battery terminal slid back over and was touching the pole....


Remove unit. no visible damage to the circuit board. Patch still holding...reinstall...so here's what I have:


1: No instrument lights.

2. Left turn signal works

3. Right turn signal does not

4. All exterior lights work. Hi / low beam okay.

5. No fuses blown in engine bay.


So besides learning how to tie my negative cable away from the battery..does anyone have and thoughts? Any help would be appreciated.

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I think the LEDs have polarity? Have you tried reversing them for the sockets that are not working?


And I know a fellow really well that has to put a patch on his 521 circuit board tomorrow. I er I mean he did this yesterday.


I'm trying to find Danielc's post where he has the pin out for the cluster so you can trace the power to see if you have a break somewhere

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Using my pin out diagram above, connect 12 volts negative to the ground pin.  Apply 12 volt positive to right turn, left turn, dash light, and high beam, those lights should come on.

Apply 12 volt positive to the Ign power in pin, leaving 12 volt negative on the ground pin, and then grounding the oil light pin, and the IGN pin those lights should come on.

With the ground still connected, and 12 volt positive on the ign power in pin, grounding the temp sender pin should cause the temp gauge go to full hot.  Grounding the gas sender pin should cause the fuel gauge to go to full.

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Had the unfortunate situation you had, luckily mine was just the common dashlight path repair. In the future remove both battery terminals. LEDs(light emitting diodes) are polar, you may have blown them from reverse installation.

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Well....looks like there were many Gremlins helping me with this project because I found all of this...


1. My jumper wire was fried again, so I went to Radio shack and bough some real jumper connections...resoldered.

2. Right turn signal bulb out, changed. nothing. Replaced original turn signal relay and all good.

3. Must have jostled my patch job from last year when I rewired headlights...wire had pulled loose. Redid correctly with connectors

    and new wires, inline fuse. I jumped the stock fuse link and made it inline....crimped and secured... headlights back.


So there you have it..just a bunch a weird little things that happened in a row.  At least I know my headlight / dash lighting system down now.

Needed an excuse to work in the garage and have a couple beers anyways!


As one who believes in paying it forward, if anyone would like LED's for their truck, I have 5 more left over.  Amazon has great deals and I bought a 10 pack

of bulbs. it was cheaper than 2 LED's for $20.00 at the auto parts store. Let me know. Ben

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