Hardwire to dome light instead of fuse panel?

[DarkSky]

I'm booking my truck in to get my F770 hardwired so that parking mode works - would it be easier (or would it even work) to just use the wires that are already close to the dashcam which power the interior dome lights?

I've seen most people wire directly to their fuse panel, but I thought - if the dome light wiring is already right near the dashcam, why not use that circuit?

yes/no?

 

[jokiin]

depends if it gives you what you need, permanent and switched power

 

[Dee_82]

dome lights tend to be controlled by a car module which usually turns the lights off after a period time, the best solution is not always the easiest one.
to be honest, depending where you fuse box is, its pretty easy to go across the roof liner then don the A pillar (front one) the car trim usually comes off really easily as will the door seals its really not a big job

 

[cacherjoe]

Also the dome light's contant power wire wouldn't be in the roof where the light is, it would be at the switch that activates the light. The wires leading into the light would not be powered until the switch is closed.

 

[DarkSky]

Also the dome light's contant power wire wouldn't be in the roof where the light is, it would be at the switch that activates the light. The wires leading into the light would not be powered until the switch is closed.

Aaah ok. I thought constant power went to a switch at the light, and it was controlled from there. I guess the only way to tell is use a multimeter and read the volts on the fuse that controls the dome lights. 'Shut the doors and see if after the lights go off, if there's still 12V showing on that fuse.

 

[Rocketvapor]

Pop the little lens cover and measure voltage at the dome light bulb. From one contact to ground then the other.
Not across the bulb

The old way was to power the light and switch the ground. The door pin switches would just ground a wire. The 12 volt came from a body feed fuse that was likely live all the time.
See if the 12 volts is switched or the ground is switched. If you can turn the dome light on from a switch at the dome light it probably has 12 volts there.

Switched ground would allow door pin switches, a time delay module or a local switch at the dome light to supply a ground.

 

[Ralph2]

Also the dome light's contant power wire wouldn't be in the roof where the light is, it would be at the switch that activates the light. The wires leading into the light would not be powered until the switch is closed.

True.. but if there is a local switch to turn the light on (most reading lamps) then there is always on power available. What with wiring for the mirror, sun roof and reading / dome lights there likely is all the power sources you need up there.

 

[Rocketvapor]

The reason many dome lights, maybe not all but many, use ground switching it to reduce the chance of short circuits.
If the key lock/entry electronics can turn ON the dome light, a switch on the dash can turn ON the dome light, a Door open pin switch can turn ON a dome light, and a switch at the dome light itself can turn ON a dome light this can all be accomplished with a single HOT wire from a fused circuit. One hot wire up through the head liner.
Ground the dome light with a local switch, a dash switch, any door pin switch, an open collector electronic switch instead of a bunch of hot wires hidden in the overhead.
That same HOT wire could be used to power those cute little aircraft style reading lights and a DOME light.

 

[DarkSky]

I've decided to just run the cord along the headliner, down the side, and into the fuse box.

'Found the constant-on (battery) fuse no problem (tons of them). I just can't find an ignition-only-on fuse in the inside fuse box. I might have to run a cord from the fuse box under the hood... and probably drill through the dang firewall. Grr....

 

[Rocketvapor]

Radio fuse? Does your radio cut off with the key?

 

[Ralph2]

A good switched source is the radio. Your cigarette lighter will also.. likely, be on a switched circuit.

 

[Dee_82]

not always, most radios will work on both ignition on and direct. I good one is usually the IC, or mood lighting if you have it, turn car off, the with a multi meter check fuses until you find on without any voltage, turn ignition on, see if it registers on the metre. There will be ignition on circuits in the car. If you must use the main fuse box at the engine the just punch a tiny hole through the gromit , push cable through the silicone seal it on the outside

 

[Ralph2]

Unless you are driving some pre 1970 model avoid going through the firewall if at all possible. Short of taking the engine out it.. is really hard to find a space to safely do it..

 

[Dee_82]

Unless you are driving some pre 1970 model avoid going through the firewall if at all possible. Short of taking the engine out it.. is really hard to find a space to safely do it..

nonsense, I wouldn't recommend it simply because there will be a fuse in side that will do the job but its not hard at all, find the large gromit on the firewall where the main body control modual / powertrain harness passes through, itll be the size of a baseball and about 1cm thick rubbber

 

[Ralph2]

nonsense, I wouldn't recommend it simply because there will be a fuse in side that will do the job but its not hard at all, find the large gromit on the firewall where the main body control modual / powertrain harness passes through, itll be the size of a baseball and about 1cm thick rubbber

Yes.. there are grommets on the fire wall where the original wires go through the fire wall.. BUT.. unless you are a contortionist it is not easy. I.. wanted to run trailer wiring from the battery to foot well.. (2011 Toyota Highlander) and found the recommended way was to remove the driver side wheel.. remove the fender trim and then get access to to where the parking brake goes through the fire wall and use that grommet.
Certainly in the OP's case finding an interior fuse is the easiest way to go by far.

 

[Dee_82]

you may have a point, I did it on a focus mk2 a while back and it required me lying on my back with my feet in the air and my head in the footwell, wasn't pleasant, but certainly not as bad as removing the wheel, wheel liner and wing itself, with hind sight on that car I should have jut taken the seat out!