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1990 Grand Prix: Lights on all the time
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scottster
New User
Nov 6, 2006, 10:11 PM
Post #1 of 4
(1584 views)
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1990 Grand Prix: Lights on all the time
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Hi there,
I just purchased a 1990 Pontiac Grand Prix. It's a great car, but has a few kinks...
The lights go on automatically when the ignition is turned on, as though the switch were turned on. Not just daytime running lamps, but dash lights, parking lights and all.
The problem is I can't read the digital readouts during the day, because they are in dim "night time" mode. Fiddeling with the light switch has no effect either.
Any ideas? Thank You!
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steve01832
Veteran
Nov 7, 2006, 2:47 AM
Post #2 of 4
(1580 views)
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Re: 1990 Grand Prix: Lights on all the time
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Check the owner's manual and see if there is a way to override the automatic headlights. If there isn't you can call GM to see if they can turn it off through the Body Control Module. I wouldn't pull any fuses or relays until you get a repair manual for this car and can identify them. Also, if you pull a fuse or relay to eliminate some automatic devices, don't be surprised if it kicks the Check Engine Light.
Steve
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DanD
Veteran
/ Moderator
Nov 7, 2006, 5:58 AM
Post #3 of 4
(1578 views)
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Re: 1990 Grand Prix: Lights on all the time
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Looking at the different wiring diagrams showing the lighting circuits and different options that were available back then is like looking into a plate of spaghetti; man what a mess. LOL
The only thing I came up with; is if when you play with the headlight switch; can you make the display and other lights (ashtray, radio ect) even go dimmer or go completely out; using the variable switch? It’ll be a thumb-wheel or a slide bar type of switch.
If not I would suspect the headlight switch and that the internal dimming module has possibly fused itself at one intensity?
If the dimmer switch will adjust then I would be looking at, if this system has an ambient light sensor mounted in the top of the dash or possibly in the outlet of the defroster vent.
With the sensor’s that are mounted in the defroster vent; I’ve seen that either something has fallen in and is covering the sensor or the plastic making up the vent has become deformed and again is covering the sensor. These sensors for the lack of a better word are an electric eye (photocell) and need a clear view of the surrounding light. They are also common for burning out leaving it stuck in one mode or the other. They resemble an after market’s security system’s flashing red LED.
Like I said there are so many mismatched systems that they used back then I would need the car and all my wiring diagrams together to even figure out what system I was working on.
I won’t even begin talking about the driver’s information center module (computer) which is the very closed minded, unhelpful first few years’ design of today’s body control computers. It has no self-diagnostic capabilities, not any that I’ve been able to access with my scanner anyway.
Good luck with this I think you may need it.
Dan.
Canadian "EH"
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steve01832
Veteran
Nov 8, 2006, 3:42 AM
Post #4 of 4
(1572 views)
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Re: 1990 Grand Prix: Lights on all the time
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Ahh, the good old days. The GM Tech 2 scan tool was capable of doing bi-directional tests and turning on and off certain body control functions. But, this depended on vehicle application strictly. I use the OTC Monitor 4000 Enhanced and never stood a chance at accessing BCM functions back then. It was always a 50/50 shot. As for the plate of spaghetti, now I will always be checking the noodles to see if any have tracers on them.LOL
Steve
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