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Thread: Dome lights

  1. #11
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    Probably because they could just use a simple one wire self-grounding switch, instead of a 2 wire switch like the glass bodied Vette which still needed 2 wires to the light too. Plus unlike newer cars you didn't need a computer just to simply light a bulb. It was too easy the old way, which I miss now. How many relays/switches/electronics/connections/wiring etc. do you want to troubleshoot when something doesn't work, and you have to rip the car apart to fix it? It would be my worst nightmare troubleshooting a newer
    Chevy like my 13 Tahoe, or 97 C5 that can have many random issues. The simpler the better IMO, which is the beauty of a stock trifive.
    Last edited by 55 Rescue Dog; 01-07-2019 at 03:10 PM.

  2. #12
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    Probably because they could just use a simple one wire self-grounding switch, instead of a 2 wire switch like the glass bodied Vette which still needed 2 wires to the light too.
    Like a 2 wire switch is that complicated? LOL. They already had them tooled for the Corvettes, and they NEEDED to run two wires to the light on those cars to ground the dome light even if they switched power. They didn't need to on the steel bodied cars and it goes against electrical design conventions for everything else.....where power is switched.

    How many relays/switches/electronics/connections/wiring etc. do you want to troubleshoot when something doesn't work, and you have to rip the car apart to fix it?
    As many "relays/switches/electronics/connections/wiring etc." as I need to get the functions I want. My Nomad will have automatic on headlights, retained accessory power, and dome light soft dimming because I want those things. New cars have them and I like the features. And it's pretty simple to do with the DD module and the wiring isn't that complex. Plus I'll have a lot more "complicated" electrical things like EFI, keyless entry, fan control, electronic A/C control, power windows, power vent windows, power door locks, electric hood release, digital self-dimming mirror, and more. If you don't want those things stick to the simple stock stuff that you have the ability to wire and troubleshoot.

    You keep drifting off-topic, which is WHY GM and others used switched ground to turn on dome lights. On a tri5 you save ONE connection by doing that. On a stock tri5 car you have one connection to each door switch, two connections to the dome light, and one to the headlight switch. That's a total of 5 connections. If you switched power you'd have one connection to the headlight switch ( if the switch was designed that way), two connections to each door, and one connection to the dome light for a total of 6. Getting one less connection while using more wire is hardly justification, imo, for changing the way the circuitry works for this one application. But maybe those push-on connectors were big bucks back then.
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  3. #13
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    Quote Originally Posted by chevynut View Post
    Like a 2 wire switch is that complicated? LOL. They already had them tooled for the Corvettes, and they NEEDED to run two wires to the light on those cars to ground the dome light even if they switched power. They didn't need to on the steel bodied cars and it goes against electrical design conventions for everything else.....where power is switched.



    As many "relays/switches/electronics/connections/wiring etc." as I need to get the functions I want. My Nomad will have automatic on headlights, retained accessory power, and dome light soft dimming because I want those things. New cars have them and I like the features. And it's pretty simple to do with the DD module and the wiring isn't that complex. Plus I'll have a lot more "complicated" electrical things like EFI, keyless entry, fan control, electronic A/C control, power windows, power vent windows, power door locks, electric hood release, digital self-dimming mirror, and more. If you don't want those things stick to the simple stock stuff that you have the ability to wire and troubleshoot.

    You keep drifting off-topic, which is WHY GM and others used switched ground to turn on dome lights. On a tri5 you save ONE connection by doing that. On a stock tri5 car you have one connection to each door switch, two connections to the dome light, and one to the headlight switch. That's a total of 5 connections. If you switched power you'd have one connection to the headlight switch ( if the switch was designed that way), two connections to each door, and one connection to the dome light for a total of 6. Getting one less connection while using more wire is hardly justification, imo, for changing the way the circuitry works for this one application. But maybe those push-on connectors were big bucks back then.
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  4. #14
    Registered Member WagonCrazy's Avatar
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    I did 15 minutes of google searching "why did General motors use switched ground to turn on dome lights" without anything conclusive coming up.

    I suspect its because they had a supplier (partner company owned by the GM parent) that made these 1 pole door switches from way back, and with the tooling cost...just consistently designed all their cars with this switched ground wiring plan. It was probably low hanging fruit to try and redesign it for a dual pole switch.

    Just wire it the way you want to (with switched 12v power) and move on to funner things Laszlo.
    1957 Nomad- LS1/T56 on C4 chassis
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