# Need help - 70 GTO gauge lighting question



## 70455goat (Nov 5, 2007)

All,

I didn't have any dash gauge lights on my 70 GTO when I bought it. The bulb holders don't have wires attached to them like my 69 Chevelle has. It has a circuit board that distrubutes the power to light the bulbs. I replaced the bulbs and now I have one bulb in each gauge set that works. There are about a half dozen bulbs in each. The left side has one of the bulbs that looks like it had a black wire that was attached, but its cut about an inch away from the bulb holder, and I can't find any loose black wires.

Anyone have any suggestions:
- How to get the other bulbs working.
- Is there supposed to be a wire connected to the bulb holder on the left guage set? If so, does the wire provide the 12VDC to the gauges or is it sending voltage somewhere else?

Thanks for any help.

Dale


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## 05GTO (Oct 6, 2004)

Dale,

I don't have a wiring schematic for the 70 models but I would bet that black wire connects to the body and provides negative voltage to the circuit board. Use a VOM and check for + voltage on the black wire before connecting it to a negatve source.

Here is a 1970-PONTIAC-GTO-FIREBIRD-SHOP-BODY-MANUAL-ON-CD with a BIN of $34.99 on ebay.


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## 70455goat (Nov 5, 2007)

I hadn't even thought about it possibly being a ground. I will check that out.

Thanks for the great idea.


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## VettenGoat (Jun 19, 2007)

ALWAYS check your grounds; it is one of the most overlooked areas among us gearheads. I have the old wiring harnes on my 65, but actually added an additional ground to brighten my dashlights. Make sure you have scuffed up the metal using scotch bright or some sand papers and that your bolt/screw and connector was corrosion and paint free. I've never had a curcuit board dash (surprised to hear they were on as ealry as 1970 actually) but a trick you can use on curcuit boards is to take a pencil erasor and gently "erase" any tarnish/corrosion along the soldered curcuits.
Good luck//Mike


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## 70455goat (Nov 5, 2007)

I will give the eraser a try. Thanks


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## seamus2154 (Feb 17, 2008)

I just checked my resoration guide and it looks like that wire goes from the top of the ashtray to that light. So i guess it's a ground. It is'n t that specific but that's what the picture looks like and I think i remember that when I took my dash out. Good luck Jim


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## 70455goat (Nov 5, 2007)

From the top of the ashtray huh....Is it connected to a ground lug or a bolt or what? I am going to get my flashlight and check it out as soon as I get up from teh computer. I did actually try grounding the wire and didn't notice any difference, but there might have been some bulbs that still needed to be replaced.

Thanks for taking the time to check it out,
Dale


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## seamus2154 (Feb 17, 2008)

I also have my dash out of my LeMans in my garage and checked it today. It goes from that tab to the top of the ashtray sleeve. It has some sort of copper molded or capped on the end of both sides of the wire. The wire is about 12-14 inches w/ a crimped metal end on both sides and clips in to the tab and the top of the ashtray. I guess it'sa ground.


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## 70455goat (Nov 5, 2007)

seamus2154 said:


> I also have my dash out of my LeMans in my garage and checked it today. It goes from that tab to the top of the ashtray sleeve. It has some sort of copper molded or capped on the end of both sides of the wire. The wire is about 12-14 inches w/ a crimped metal end on both sides and clips in to the tab and the top of the ashtray. I guess it'sa ground.


Thanks for checking. I will look under my dash. I don't know why someone would cut it, but they did, about an inch from where it connects to the back of the gauges.


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## Old Indian (Jul 4, 2007)

The wire you describe from the bulb to the ash tray is fiber optic line to illuminate the ash tray. Clean up both ends of the fiber and shine a light through it. If it doesn't pass the light, the ends may need to be polished.


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## 70455goat (Nov 5, 2007)

Hey thanks for the info. I gotta wonder about something though.......

Fiber Optic.....in 1970? I had't even heard of fiber in 1970.


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## Old Indian (Jul 4, 2007)

My 1969 has the same configuration. Back then, they were using optic fibers on Christmas trees and toys. I guess a few found their way into cars. 

Bill


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## seamus2154 (Feb 17, 2008)

Wow, you really do learn something new every day!!! I've owned about 11 of these cars since high school, and taken apart quite a few of them, and never new that. Makes sense now. Yeah why would they have such an end just to ground something?!!


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## BobG (Dec 20, 2006)

Yep, it's fiber optic. And, yes, they had them in 1970. I think Cadillac was the first domestic make (in the mid or late 60's) with fiber optics.


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## Eric Animal (Oct 28, 2007)

I think the printed circuit dash in GTO started in 69...fibre optics have been around since way before that...usually in those little "cat eye" lights on the fenders that tell you if lights are on/off, blown out, signal lights blinking etc.....We can thank the Space program and defense contractors/engineers for cool stuff like this.......:cheers


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## Eric Animal (Oct 28, 2007)

Oh yeah....Early form of Fibre Optics: Sailing ships from the 1600's-17OO's used to have a large glass prism mounted in the deck floor....the pointy end down into the cabin or hold below. Sun light would shine on the flush, floor of the deck, and be refracted through the cabin,hold or passage ways below....Eric Even our ancestors had cool stuff !


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## Aqua GTO 1970 (Feb 18, 2012)

Dash lights are not working checked all bulbs.bulbs are good checked ground bracket to screws on circuit board they are connected. Replaced switch no change. Is the switch supose to be grounded. This is on 1970 gto thanks


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## Aqua GTO 1970 (Feb 18, 2012)

The gray wires seem to be connect to ground is this right. One of the gray wires is not connected it is in a bunndle with orange,white,yellow and another gray that is connected to lighter


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## Aqua GTO 1970 (Feb 18, 2012)

*Dashboard lights are dim*

When i turn dashboard lights on gas gauge goes down is this a ground problem thanks for your help


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