What is this wire? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**MikeB** · 08-15-2021, 12:13 PM

When I pulled out the instrument panel 6 weeks ago, I ether took this off the back or it had just been hanging there. (In other words, I forgot!)

The black wire (probably 12 gauge) disappears up the steering column. The lug on the cylindrical terminal doesn't have continuity with either of the light bulb terminals.

So what is its mission in life?

sick472 · 08-15-2021, 12:28 PM

I'm betting that is the fiber optic cable that illuminates the shift indicator on top of the column and not a wire. If so, it should plug into the back of the gage cluster where it gets its power. I'm not sure what hole it goes in, but it would be one that is powered up when the lights are turned on.

**MikeB** · 08-15-2021, 12:36 PM

Quote:

Originally Posted by sick472

I'm betting that is the fiber optic cable that illuminates the shift indicator on top of the column and not a wire. If so, it should plug into the back of the gage cluster where it gets its power. I'm not sure what hole it goes in, but it would be one that is powered up when the lights are turned on.

That makes total sense and I feel like a dumb a$$. Pretty high tech for 1969.
Don't remember if the gear indicator ever lit up, but at least I know how to check it now. Thanks!

**Mts67C10K20** · 08-15-2021, 12:39 PM

Agree with sick472
The bulb gets power from the clucter when installed
Fiber optic to indicator...dont bend it...

**va72longhorn** · 08-16-2021, 02:17 PM

Fyi, it doesn’t actually “ get power” from anywhere. It “looks” at an illuminated light source (instrument bulb) and transfers the light through the clear conductor. When it hits the raw end, it becomes an illumination itself.
Fiber optics were out and used in many applications long before we learned that we could communicate over them. ��

**MikeB** · 08-16-2021, 04:52 PM

Quote:

Originally Posted by Mts67C10K20

Fiber optic to indicator...dont bend it...

My cable looks like it was pinched, but it still works. Will check it for brightness tonight. Also, its special bulb holder doesn't snug up in the panel as well as I'd like. All my others are new and tight. I may use a dab of silicon sealant.

Caddylackn · 08-16-2021, 04:54 PM

If the end is scratched or hazy you can polish it to increase the light output

**va72longhorn** · 08-16-2021, 05:45 PM

Alcohol wipe like you use on your glasses does a good job too.

**Thealien** · 08-16-2021, 05:56 PM

Quote:

Originally Posted by MikeB

My cable looks like it was pinched, but it still works. Will check it for brightness tonight. Also, its special bulb holder doesn't snug up in the panel as well as I'd like. All my others are new and tight. I may use a dab of silicon sealant.

Try bending the little tabs on the socket a bit. Has worked for me but not always.

08-15-2021, 12:13 PM	#1
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,609	What is this wire? When I pulled out the instrument panel 6 weeks ago, I ether took this off the back or it had just been hanging there. (In other words, I forgot!) The black wire (probably 12 gauge) disappears up the steering column. The lug on the cylindrical terminal doesn't have continuity with either of the light bulb terminals. So what is its mission in life? Attached Images __________________ Mike 1969 C10 LWB -- owned for 36 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

08-15-2021, 12:28 PM	#2
sick472 Registered User Join Date: Jul 2015 Location: Sedalia Mo. Posts: 1,131	Re: What is this wire? I'm betting that is the fiber optic cable that illuminates the shift indicator on top of the column and not a wire. If so, it should plug into the back of the gage cluster where it gets its power. I'm not sure what hole it goes in, but it would be one that is powered up when the lights are turned on. __________________ He who is without oil shall throw the first rod. Compressions 8.7:1 1972 C10 1976 C10 (parts truck) 1985 K20

08-15-2021, 12:39 PM	#4
Mts67C10K20 Senior Member Join Date: May 2017 Location: Dowagiac Michigan Posts: 202	Re: What is this wire? Agree with sick472 The bulb gets power from the clucter when installed Fiber optic to indicator...dont bend it...

08-16-2021, 02:17 PM	#5
va72longhorn Senior Member Join Date: Dec 2009 Location: Culpeper, VA Posts: 435	Re: What is this wire? Fyi, it doesn’t actually “ get power” from anywhere. It “looks” at an illuminated light source (instrument bulb) and transfers the light through the clear conductor. When it hits the raw end, it becomes an illumination itself. Fiber optics were out and used in many applications long before we learned that we could communicate over them. ��

08-16-2021, 04:54 PM	#7
Caddylackn Registered User Join Date: Jun 2016 Location: Bremerton, WA Posts: 171	Re: What is this wire? If the end is scratched or hazy you can polish it to increase the light output __________________ 1969 Custom Camper C20; Factree Air, 350/TH400/Dana 70U with C30 wheel cylinders, Disk brakes, H4 conversion, headlight relay mod, 3G 135 amp alternator. 7500 GVW

08-16-2021, 05:45 PM	#8
va72longhorn Senior Member Join Date: Dec 2009 Location: Culpeper, VA Posts: 435	Re: What is this wire? Alcohol wipe like you use on your glasses does a good job too.



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