Early OBS 12V Accessory Power

[WindsorShatzkin]

Hi,

This is a two part question.

1. Does anyone know how to (or has already) add 12V power outlets that turn off when the key is off, but are on when the key is in ACC or RUN positions?

I would assume you could just tap into the interior fuse box for accessory power...


2. Does anyone know how to make the cigarette lighter socket behave in the same fashion?

I had read on another board that you would need to add a relay (activated by accessory power) and possibly a diode (to eliminate discharge from the relay during power-off) to make the cigarette lighter socket work.


Thanks.

 

[BoxerPitMix]

What year is your truck? I'm not really familiar with the wiring of pre '95ish trucks, so if it's older than that someone else may have to chime in on where to tap into for your relay.

Ok so I THINK this is right, I just took another diagram I found from Google and edited it in MSpaint.

86 Needs to run to an accessory that is on with the key. You can grab this from a few places - the back of the radio I believe is a Yellow wire for keyed power, or from the ignition harness below the steering column from a thicker Pink/White or White (Been a long time since I worked on this stuff, test it first). Don't touch anything with a yellow plug or yellow cover over the wires - that's the airbag!
Or the quickest way would probably just to tap into the fuse box onto something like the radio fuse.

30 I would run either to the battery or the post on the fuse box beneath the hood with a fuse.

85 of course is ground... You could probably use the existing ground from the old lighter (black) but you could also run it to the battery, frame, wherever you felt comfortable. Same goes for the ground to your power outlet.

87 is the + side to your power outlet. I dunno if you'd need to worry about discharge when the key is off... But you could diode isolate it if you like. Just put it in line with the + to the outlet I'm guessing?

If I'm wrong on any of this stuff I'm sure someone else will jump in.

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[WindsorShatzkin]

My truck is an 89. Although I think the 88-94 trucks are the same.

This actually helps a lot. Thanks! Luckily, I won't have to watch out for the airbag wire. My truck doesn't have one.

Someone on another board mentioned the possibility of just changing the + wire on the cigarette lighter from constant hot to accessory, with an in-line fuse. Same for any additional outlets added. This would remove the need for the relay. Do you think that would work? Or would you use the relay anyway?

 

[BoxerPitMix]

You could probably do that, but you'd be drawing power off the accessory circuit where other things are already running. I'd probably just use a relay regardless. You could actually just run the existing wire that goes to your lighter through the relay so that it only sends power to the plug whenever the key is on.

 

[someotherguy]

On 88-94, if you operate a relay using power from one of the terminals marked BLU in the under dash convenience center, it will only operate while the key is in the RUN position. Example; see the yellow wire with the crimp-on terminal (this is used for power to my transmission temperature gauge):

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I don't recall right off hand but I think that the WHT terminals are powered in both ACC/RUN. Easy enough to find out with a test light.

Be sure to use a relay.

Richard

 

[WindsorShatzkin]

Richard, thank you so much!

Do you mind if I ask you what relay you used? And if you used a diode in your circuit?

I'm primarily using this for power to a bluetooth AUX-In (after I do the AUX-In radio conversion) and one to two phone chargers. I was going to change the factory cigarette lighter socket to a 12v power socket, and then add one additional 12v power socket.

 

[BoxerPitMix]

I always had horrible luck with car chargers for my phone - seemed like they always ended up dying and are expensive. Most everything I have these days I have a USB cord to. This is what I ended up replacing my lighter with.

 

[WindsorShatzkin]

Honestly, that's what I should do with my second (the future add-on) power outlet. I was only going to put my double USB port charger into it anyway.

Where did you buy your USB power outlet?

 

[someotherguy]

Richard, thank you so much!

Do you mind if I ask you what relay you used? And if you used a diode in your circuit?

I'm primarily using this for power to a bluetooth AUX-In (after I do the AUX-In radio conversion) and one to two phone chargers. I was going to change the factory cigarette lighter socket to a 12v power socket, and then add one additional 12v power socket.

My application didn't need a relay as I'm just powering a simple analog gauge. It sounds like you're looking to power higher-load items through the cig lighter, so that's why I'm suggesting you operate a relay with the circuit instead of putting the load on the circuit.

Boxer - nice mod! I've had pretty good luck with car chargers but I try to stick to brand names, especially since the BlackBerry branded "premium" car charger is 1.8A and charges my phone up really fast. If 88-94 had multiple sockets I'd probably set one up like that in the black '94...may still do something similar one of these days, just for other purposes.

Richard

 

[dmr22]

Boxer, that is awesome! Where did you get the USB port?