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1991 Cherokee Laredo, 3.5" Rubicon Express lift, 31" BFG Mudders, Smittybuit F/R Bumpers...
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Discussion Starter · #1 ·
So, I decided to pull the dash gauge cluster out and replace all the bulbs with red LED bulbs as they generate less heat, are more power efficient, and I like red interior lights at night.

But, the back of the dash doesn’t show polarity on the Mylar traces so I was not able to determine accurately which trace is positive and which is negative. For incandescent bulbs it doesn’t matter, but for LEDs it does. When I put the dash back in and tried testing I immediately blew the console fuse (7.5 amp). I tried this process four more time and finally gave up and put the old bulbs back in.

229503


229504


I have original Jeep shop manuals for the ‘91 but following all the schematics is beyond my capabilities…

Does anyone here have experience with this kind of upgrade?
 

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1991 Cherokee Laredo, 3.5" Rubicon Express lift, 31" BFG Mudders, Smittybuit F/R Bumpers...
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35 Posts
Discussion Starter · #3 ·
For the main cluster I was able to use a multimeter to identify, what I thought, were all the grounds. I then oriented the bulbs in what I thought were the correct positions. For the smaller bulb area (left side sitting at the wheel) that was not possible. So I tried using the schematics to identify positive and negative. But, in four tries, I was not able to get it to work. I’d reinstall the dash, reconnect the battery, and then start the engine. Every time none of the gauges worked and the dash fuse blows.

I’d expect that the LEDs simply wouldn’t light up if the polarity wasn’t right so I’m not sure why the fuse is blowing. But, swapping back to incandescent bulbs fixes everything… very strange. And I can’t imagine that the LEDs are pulling more power than the incandescent bulbs did, but maybe…
 

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1991 Cherokee Laredo, 3.5" Rubicon Express lift, 31" BFG Mudders, Smittybuit F/R Bumpers...
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35 Posts
Discussion Starter · #8 ·
Not sure who the “and your question is” is directed at, but I’ll assume me…

I didn’t really have any question beyond the original info. When I tried to install replacement LED “bulbs” into the instrument cluster I was not able to easily determine which trace on the “board” was positive and which was negative. Several were obvious and tested out fine using my multimeter, but others were not. And strangely, the cluster fuse blew every time I connected things back up. So, I just put the old bulbs back in and stayed incandescent.

The question, if I didn’t directly ask it before, would be, why would using LEDs (polarized) cause the fuse to blow? I’d think the worst case would be some LEDs simply wouldn’t work if they didn’t get put in the socket with the correct polarity. I did not expect to blow a fuse. Resisters would be required for the signal bulbs, but I don’t think they’d be needed in the cluster.
 
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