12V switched source (even while cranking)

[JeffSnAusTX]

Hey folks,

I'm in need of a 12V ignition switched source... that will provide a constant 12V even when the starter is engaged. My boost gauge needs a constant source to do accurate auto zero'ing.

The white/green wire that many use isn't constant - it is denied power when the starter is engaged.

Thanks in advance for your help.

 

[JeffSnAusTX]

Thought I'd share for anyone who does future searches (I've found lots of answers via searches).

The blue/yellow wire (on a 3 wire connector) behind the change compartment will provide a constant source for 12V, even while starting the motor. My boost gauge zero'd and reads exactly what was expected :top:

Cheers,

Jeff

 

[Spyder327]

Glad you got it taken care of :top:

 

[AFP520]

Not a bad idea for me to switch my radio switched power to that. The double din's take longer to start up.

 

[5H4D0WD347H]

One of the wires on the spare plugs you are speaking of by the change compartment is tied into the light switch on the column, so watch which one you use or everything will cycle on/off with the running lights.

Check out this link for some more ideas, the second page has a link to an entire common wiring break down.

 

[trd_sport]

where are you all with the TRD boost gauge wiring it to? Mine doesnt have instructions on what 12v source to use.

 

[AFP520]

One of the wires on the spare plugs you are speaking of by the change compartment is tied into the light switch on the column, so watch which one you use or everything will cycle on/off with the running lights.

Check out this link for some more ideas, the second page has a link to an entire common wiring break down.

Which link? :dontknow:

 

[5H4D0WD347H]

Which link? :dontknow:

:laugh: Excellent question!

http://www.xr-underground.com/vb3/showthread.php?t=7573&

 

[AFP520]

:laugh: Excellent question!

http://www.xr-underground.com/vb3/showthread.php?t=7573&

Was that one of the wires that provided constant power even when the starter is in use?

 

[5H4D0WD347H]

You should run a fused (fused near the battery) power lead from the battery into the truck to provide a common source for other accessories & gauges in need of a constant 12V source.

Your switched IGN lead is that wire under the dash.

You usually need both for gauges... The cycling of the IGN 12V is what triggers calibration of certain gauges/senders while the constant 12V is the source.

 

[AFP520]

You should run a fused (fused near the battery) power lead from the battery into the truck to provide a common source for other accessories & gauges in need of a constant 12V source.

I see what you're saying, but my head unit already receives a constant power. What I'm looking for is a constant "switched" source of power from the ignition.

Example: When you turn on your truck, your radio will begin to turn on. I have a double din, which takes about 10-15 seconds to start up and actually become usable. Every time I go to start the truck though, the radio will reset because the switched power was interrupted at some point.

I'm trying to make it that when I turn the key in the ignition, the radio continues to start without resetting from the starter.

 

[5H4D0WD347H]

You would then need to wire in a relayed 12V into that switched IGN lead... this may cause problems though if it backfeeds into other things connected to that lead; you need a circuit diagram.

I am pretty sure the radio would be the only thing affected though (and what ever else you have being powered off that circuit).

 

[AFP520]

You would then need to wire in a relayed 12V into that switched IGN lead... this may cause problems though if it backfeeds into other things connected to that lead; you need a circuit diagram.

I am pretty sure the radio would be the only thing affected though (and what ever else you have being powered off that circuit).

The only thing I'm thinking I could do would be a relay, but that wouldn't matter as the wire is still being cut off by the starter.

This sucks. :laugh:

 

[5H4D0WD347H]

It wont be cut off by the starter if the trigger source of the relay is not cut off.

 

[AFP520]

It wont be cut off by the starter if the trigger source of the relay is not cut off.

So I'd need to find a fuse under the hood that acts as switched power, right? I could use a test light.

 

[5H4D0WD347H]

So I'd need to find a fuse under the hood that acts as switched power, right? I could use a test light.

Yes or anything that comes on in the truck when you get in (or insert the key) that stays on.

Or just use a toggle switch... :laugh:

 

[JeffSnAusTX]

Sorry for resurrecting a dead thread... but more info....

Same connector many "tap" into for power.....

blue = constant 12VDC, feeds into ignition switch and results in the two below (both fed back to the fusebox):

blue/yellow = switched 12VDC, present while starting
white/green = swtiched 12VDC, not present when starting

I'm using an OEM "pigtail" (from the OEM security add on) and the Viper's "retained accessory output", along with a 60A SPST relay to keep my accessories powered until the doors are opened (the only one I'll be using is the head unit). The purpose of the pigtail is so I don't have to hack into the large ga wires in the ignition harness. I can unplug it and return everything to normal op.

**There is serious current moving through these wires (as high as 50A). If you decide to do anything in that area, do your homework or smoke will fly**

Huge thanks to DS for his help with what has become one he** of a project :top: