Mystery speedometer mod

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n_l
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Joined: Wed Jun 28, 2017 8:45 pm
Location: Boston, MA

Mystery speedometer mod

Post by n_l »

I've disassembled the instrument cluster of my '84 633CSi to fix broken odometer gears and a non-functional MPG gauge and came across the pictured what-I-believe-to-be-a-mod on the back of the speedometer. I know somebody's been in the cluster before me as it has a new, non-battery SI board, but I'm at a loss as to what somebody thought they were doing with this. Any ideas? Does anyone have a detailed speedometer schematic that could help me track this down?

Thanks,
-noam
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Pod
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Re: Mystery speedometer mod

Post by Pod »

Looks as if it’s been fitted for quite a while. What is on the other side of the board? It looks as if something has been bridged with the fuse to protect it.
n_l
Posts: 7
Joined: Wed Jun 28, 2017 8:45 pm
Location: Boston, MA

Re: Mystery speedometer mod

Post by n_l »

The other side of the board has two metal-sleeved holes, so it looks like something is supposed to stick in there, but I'm not sure what - that's why I'm looking to see if anyone has a detailed speedometer schematic. If I knew WHAT it was connecting, I might be able to determine why...

I've read about a fuse that opens on mileage to trigger a warning light (like VW used to do with it's every-60k-oxygen-sensor light), so maybe someone wanted a permanent fix to that...
baders
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Re: Mystery speedometer mod

Post by baders »

There is a fuse (0.1a) which, when it blows at 30,000 miles, closes a switch to bring on the O2 sensor light on the active check panel. That fuse that has been added to yours is however a 3a. If you have an instrument specialist around, best to take it to them.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
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