# idiot lights.....68 lemans



## poncho power (Nov 28, 2012)

I hate to keep bothering you guys with all the little problems I'm finding with this car, but I figure who better to ask, then the guys that have been through it?

Idiot lights.......
My oil pressure light works perfect, turn key on, light is on. start the engine, in a couple seconds light goes off....

Generator light....
turn key on, and no light..... when I crank over engine it comes on, but as soon as engine starts and I let off the key, the light goes off.... Isn't the light suppose to be on when the key is in the ON position ? Well, it is not.

Temp light.....
This light I cannot get to come on at anytime. I changed the light bulb, and still nothing... I unhooked the wire at the temp sender, and nothing..... So then I grounded the wire at the sender to a good ground, and still nothing.... I did that with the key on, still no temp light... 

I'm really not sure what to try next.... any ideas would be great... thanks guys...


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## 05GTO (Oct 6, 2004)

Place the positive lead of your volt meter on the battery positive post, connect the negative lead of the meter to the dark green t-stat wire (unpluged from the temp sensor), turn on the switch. You should read 12-13 volts. If you don't check the grounding for the keyswitch.

The idiot lights receive their positive voltage thru the pink wires, check the splice points behind the dash.


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## poncho power (Nov 28, 2012)

05GTO said:


> Place the positive lead of your volt meter on the battery positive post, connect the negative lead of the meter to the dark green t-stat wire (unpluged from the temp sensor), turn on the switch. You should read 12-13 volts. If you don't check the grounding for the keyswitch.
> 
> The idiot lights receive their positive voltage thru the pink wires, check the splice points behind the dash.


Thanks, I will give that a try tomorrow... 

How about the Gen light, shouldn't that light be on in the ON position? Mine only comes on in the cranking position.


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## poncho power (Nov 28, 2012)

Ok, so I checked the temp wire today, and it was just the opposite of what it's suppose to do. I lad 12 volts with the key OFF, but when I turned the ON, the voltage went down to .500V. I wonder if I have a ground problem? The guy before me had painted the firewall, inner fenders, etc.... I'm wondering if he cleaned contact surfaces under ground straps? I might have to do some more digging.


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## BearGFR (Aug 25, 2008)

Check for blown fuses. On my 69 there's one in particular that supplies power to the gauges/indicator lights. Now, I know what you're thinking - "but the lights come on sometimes so it can't be a blown fuse". Yes it can. The way the alternator indicator light circuit works will feed power to the lights/gauges "in reverse" even if the fuse is blown (and it will also make your alternator light "act funny").

Bear


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## poncho power (Nov 28, 2012)

BearGFR said:


> Check for blown fuses. On my 69 there's one in particular that supplies power to the gauges/indicator lights. Now, I know what you're thinking - "but the lights come on sometimes so it can't be a blown fuse". Yes it can. The way the alternator indicator light circuit works will feed power to the lights/gauges "in reverse" even if the fuse is blown (and it will also make your alternator light "act funny").
> 
> Bear


But my oil pressure light works perfect, wouldn't that rule that out? And IT actually did check all the fuses before looking for anything else, so ???


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## 66 Gas Tires Oil (Oct 23, 2012)

i bet your bulb is burnt out. you should not see voltage at your sending unit. think of the sending unit as a switch. it is open (off) when cold. it closes (on) when overheated. it completes the circuit for the light buulb by giving the negative potential. with your key in the on position, placing the the sending unit wire to the negative battery post or engine block the light should go on. if the bulb is good, you may want to ohm out from the sending unit to the bulb socket. the wire goes through the bulkhead connector. i wired plenty of these cars. this past weekend the 66 i just got had the temperature bulb plugged into the brake light indicator.


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## poncho power (Nov 28, 2012)

Well, I did replace bulb right away, and that wasn't it... should the temp light come on with just the key on? Not running, but just key ON? If so, how does the sender ground the circuit then when the engine is cold?


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## 66 Gas Tires Oil (Oct 23, 2012)

the temp light comes on when you engine is overheating. it basically warns you to turn off your engine or you will do damage to it. it only gets a negative to the bulb at that time. oherwise the switch (sending unit) is off.

jim


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## gjones (Oct 8, 2012)

*idiot lights*

Like '66 tires, said-check that the bulbs are plugged into their proper holes behind the dash. That'll throw the whole ball of wax off in a New York minute. Also check dash grounds.


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## poncho power (Nov 28, 2012)

gjones said:


> Like '66 tires, said-check that the bulbs are plugged into their proper holes behind the dash. That'll throw the whole ball of wax off in a New York minute. Also check dash grounds.


My 68 dash has a circuit board on the backside, so you can't plug them in the wrong spot. I didn't get a chance to work on it today, but I will dive into it tomorrow... I'm wondering about the dash having a good ground also, I will have to see if I can find it...


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## 66 Gas Tires Oil (Oct 23, 2012)

your not understanding it. the negative comes from the temperature sending unit. dash is not in the equation it just supports the bulb in this type of circuit. there are two wires going to the socket. pos from the key and neg from the sender. read my posts untill it sinks in otherwise take it to a mechanic and have him show you how it works consider it paid training. for some folks, electrical devices are hard to undertand but that is ok you got to start from somewhere. good luck.

jim

:seeya


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## poncho power (Nov 28, 2012)

Yes, I do understand it, BUT, I already grounded the temp wire to the Bat ground, & the light does not come on. I will dig more into it today.


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## poncho power (Nov 28, 2012)

SUCCESS! Found a connector under that dash that was not good anymore. Someone had cut and spliced a ground wire. I had the temp sender wire grounded to the battery, & then I went under the dash and started moving wires around, when all of a sudden saw the light flicker.... sure enough the wire was barely holding on to the butt connector. Repaired the connection, and now it works..... thanks for the help on that one.


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## gjones (Oct 8, 2012)

*ground*

Excellent news!!! Wiring mods. done by PO's will always get you in the end! Most times it usually IS a rusty/bad ground that is the source of consternation, though!


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## PontiacJim (Dec 29, 2012)

You say the last owner painted the firewall. He may have disturbed some wires or removed them to paint. I learned this one my self - make sure you have a grounding strap from the engine to the firewall. The factory one, as I recall, is a braided strap. You mentioned this, check to see that it is not broken, corroded, or the attachment bolt/screw stripped out on the firewall from over tightening. I was having a problem burning out voltage regulators. Finally figured that one out. I was the one who pulled the ground strap off when I rebuilt the engine. A Ground strap is very important. I also experienced on another GTO an Alt light problem. I found a broken wire inside the plastic casing in the engine compartment. It looked perfect on the outside. Used an Ohm meter to test the wires, one at a time, going from the engine side to the dash side. Tedious, but that's how it is done sometimes.


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## poncho power (Nov 28, 2012)

PontiacJim said:


> You say the last owner painted the firewall. He may have disturbed some wires or removed them to paint. I learned this one my self - make sure you have a grounding strap from the engine to the firewall. The factory one, as I recall, is a braided strap. You mentioned this, check to see that it is not broken, corroded, or the attachment bolt/screw stripped out on the firewall from over tightening. I was having a problem burning out voltage regulators. Finally figured that one out. I was the one who pulled the ground strap off when I rebuilt the engine. A Ground strap is very important. I also experienced on another GTO an Alt light problem. I found a broken wire inside the plastic casing in the engine compartment. It looked perfect on the outside. Used an Ohm meter to test the wires, one at a time, going from the engine side to the dash side. Tedious, but that's how it is done sometimes.



Jim....
I got the temp wire repaired, so that light comes on now when I ground the wire at the sender.
I still have an issue with the BAT light not coming on all the way with the key in the ON position. It has a real faint glow, just enough that I can see the light on. When I start the engine, the light goes all the way off, and the engine is charging. I still wonder why that light only comes on faintly when I have the key in the ON position though...?


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## gjones (Oct 8, 2012)

*wiring*

That sounds like a grounding problem to me. On the '66, at the rear of the dash, there is a metal grounding bar that attaches to the steering column. I forgot to tighten that up securely and had very strange dash light operation. Was a really quick and easy fix. Not saying that's your problem, but it may be worth a look. Also, have you pulled the fuse box and inspected the terminal ends and connectors? Mine were RUSTY. Took FOREVER to clean and deoxidize, but well worth it, saved a bundle of cash, and after all said, was gratified to still retain the original wires (NICE) and fusebox, with fresh loom tape. I also installed 4 new engine to frame/firewall/body ground straps. All is swell in electric land. And as Pontiac Jim said, check those old wires laying on top of the engine going to the alternator which have heated and cooled 100,000 times. They get mighty brittle after 45 or so years. May the Pontiac gods smile upon you!


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## 1qwik99 (Mar 12, 2012)

*Temp light*

My temp light comes on when the car is running. I disconnected it a long time ago because I am now using a 2 wire alternator and no regulator and am using a AEM digital temp gauge. How do I turn the light off permanently. Same issue with the batt light. Do I just ground them?

Thanks

66 GTO


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## Stereolab42 (Apr 6, 2018)

Sort of a necro but this is a great thread and I have a similar problem with my temp idiot light (the only one I don't have working yet). If I ground the dark-green wire going to the temp sender when on IGN 1, the light goes on. But with it plugged into the sender on IGN 1, the light does not go on. On the back of the ignition switch there are two green wires going into a single prong... one green wire is from the sender, and the other green wire is from the idiot light on the gauge (and my voltmeter confirms this). Now if I understand the theory right, on IGN 1 the ignition switch should be internally grounding this prong in order to complete the circuit and light the light. So I think my ignition switch has some internal breakage that prevents this grounding, right?


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## Stereolab42 (Apr 6, 2018)

Stereolab42 said:


> Sort of a necro but this is a great thread and I have a similar problem with my temp idiot light (the only one I don't have working yet). If I ground the dark-green wire going to the temp sender when on IGN 1, the light goes on. But with it plugged into the sender on IGN 1, the light does not go on. On the back of the ignition switch there are two green wires going into a single prong... one green wire is from the sender, and the other green wire is from the idiot light on the gauge (and my voltmeter confirms this). Now if I understand the theory right, on IGN 1 the ignition switch should be internally grounding this prong in order to complete the circuit and light the light. So I think my ignition switch has some internal breakage that prevents this grounding, right?


Nope, the idiot light was in fact between my ears. Turns out TEMP only gets test-lit on IGN 2 (ground is established through the switch for the duration of you cranking the engine), whereas GEN and OIL get test lit only on IGN 1 (via some different mechanism) Not sure why I didn't notice this. Well at least I know all my dash lights are finally working.


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