Proper way to pull a 12 volt supply?

[glmoore001]

I do not have a lot of experience with automotive electrics. I can read a diagram, I can solder. I managed to rewire my Shovelhead without burning it down.
There are many things I do not know though.

I have to pull a hot wire, a ground and a dimmer wire for my ISS Pro FP Gauge install.
I will pull the dimmer wire from the dash light dimmer wheel most likely. But where do I pull the 12volts?

Ok, I realize I could just put on some ring terminals and come off the battery, I have military terminals, but there is too much junk there already.
I poked around in the fuse boxes with a DVOM yesterday hoping for a hot connection in an empty slot, but there were none.

My Fass pump is using a piggyback fuse plug in a 10 amp accessory hole in the interior fuse box, not wild about that. That connection is plugged into an accessory circuit and is a pita. I prefer to switch that location to make it ignition only, but unsure which to fuse slot to use. I would actually prefer if it was hardwired in somewhere.

So, what is the proper, non hack way to grab 12 volts from a system?

Thanks.. Gary

 

[TMyers]

Here is the "Cleanest" way to do that I've found. https://www.ebay.com/itm/4-Way-Fuse...513782?hash=item3d5cf436f6:g:F5AAAOSwAtlaqz9s

 

[mwilson]

For a situation such as yours I would recommend one of these. They are available for most styles of automotive fuses. They don’t put extra pressure on the fuse cavity like the taps do.

 

[glmoore001]

Here is the "Cleanest" way to do that I've found. https://www.ebay.com/itm/4-Way-Fuse...513782?hash=item3d5cf436f6:g:F5AAAOSwAtlaqz9s

That is pretty nice and would be a great solution.
If I wanted it "on" only with the ignition, any idea where I would splice it in?

 

[BoeingDiesel]

I've heard that some will use the oil pressure sensor to get power with key on. I used ( I think ) the black wire with grey stripe on the steering column but you can easily choose the correct wire with a continuity tester.

 

[TMyers]

That is pretty nice and would be a great solution.
If I wanted it "on" only with the ignition, any idea where I would splice it in?

I have two 12v accessory plugs inside the cab. One is switched, the other on all the time. Is your cigarette lighter switched?

 

[DavidC]

The proper way to do the fass if not already done. Pull 12vdc from the battery to a Fuse holder then to a normally open relay base common terminal. From the normally open contact to the pump. The original 2 wires that fed the pump (original) will go to the relay coil from the ECM. Be sure to have a diode across the relay coil to prevent spikes back to the ECM. As far as the pressure gauge I will have to look that one up, I have done it and requires removal of the knee bolster some peeling of wire insulation and soldering. If I ever wake up I will check it out.

Dave

 

[DavidC]

I am AWAKE.
This is the ignition switch and I believe I used the Dark Blue which powers during Start and Run. Black/White tracer during Run, Accessory ( No real need to power pressure in Acc. I don't think).

Dave

 

[BoeingDiesel]

Spot on Dave, my FP gauge activates in accessory position which is useless but I didn't want to go back and look for another. GLmoore, there is a video on youtube that gives fairly detailed info in pulling off power from the steering column cluster and I looked high and low today but cannot find it. It's a fairly straight forward process.

 

[DavidC]

Spot on Dave, my FP gauge activates in accessory position which is useless but I didn't want to go back and look for another. GLmoore, there is a video on youtube that gives fairly detailed info in pulling off power from the steering column cluster and I looked high and low today but cannot find it. It's a fairly straight forward process.

If you pull the knee bolster (Very easy) there is a wad of wires coming down the column. I just sifted thru them to find the dark blue, stripped off a little insulation, wrapped the wire around the existing, soldered then taped. For me it worked well as no contortioning and weird unorthodox positions needed. If the one you state is easier I am all for it.

Dave

 

[BoeingDiesel]

No easier way that I know of and that's exactly the way I did it. I pulled the knee bolster and the cover off the bottom of the steering wheel to expose the harness connector that attaches to the ignition switch.

 

[glmoore001]

The proper way to do the fass if not already done. Pull 12vdc from the battery to a Fuse holder then to a normally open relay base common terminal. From the normally open contact to the pump. The original 2 wires that fed the pump (original) will go to the relay coil from the ECM. Be sure to have a diode across the relay coil to prevent spikes back to the ECM. As far as the pressure gauge I will have to look that one up, I have done it and requires removal of the knee bolster some peeling of wire insulation and soldering. If I ever wake up I will check it out.

Dave

My relay is hanging in back of the wheel well from a wire tie. It is very sloppily installed and open to the environment of the bottom of the truck. I bought a waterproof relay on Amazon to replace it and was going to install under the hood, but if I have the wiring diagram of the relay figured out correctly, I have bought one with no diode. The relay is wired direct to the battery, there is another wire coming from the same loom that goes to a fused wire tap in an accessory slot in the in cab fuse box. I just assumed this was part of the Fass also. Maybe not. I could always pull it and see if the pump stops I guess.. Anyway, no fuse in the system that I can see if that wire tap is not part of the system. My original block mounted lift pump is still wired up to the original harness so I do not believe I am pulling a signal from the ecm at all. Is that possible? The pump just runs all the time anytime the ignition or accessory is on.
Sorry to be so ill informed about what is going on with the truck. I have chased so many problems on it since I have gotten it, I have not made it to the Fass wiring yet. Gary

 

[glmoore001]

I have two 12v accessory plugs inside the cab. One is switched, the other on all the time. Is your cigarette lighter switched?

I believe it is. Actually right now I believe the fuse is blown, no power the last time I tried the gps in that one. I will take a closer look this weekend. Thanks

 

[glmoore001]

If you pull the knee bolster (Very easy) there is a wad of wires coming down the column. I just sifted thru them to find the dark blue, stripped off a little insulation, wrapped the wire around the existing, soldered then taped. For me it worked well as no contortioning and weird unorthodox positions needed. If the one you state is easier I am all for it.

Dave

I believe the one I was talking about was for the dimmer connection on the lighting. I hope there is a wire coming from the dimmer switch. I had no idea where to pull the 12 volt power.

 

[glmoore001]

I am AWAKE.
This is the ignition switch and I believe I used the Dark Blue which powers during Start and Run. Black/White tracer during Run, Accessory ( No real need to power pressure in Acc. I don't think).
View attachment 107501
Dave

Thanks Dave, I can get it from this drawing.

 

[DavidC]

I believe the one I was talking about was for the dimmer connection on the lighting. I hope there is a wire coming from the dimmer switch. I had no idea where to pull the 12 volt power.

Dave

 

[Road Dog]

Personally, the radio harness as everything you need +12 battery, +12 switched, dimmer and ground. Use an inline wire tap to connect.

 

[DavidC]

Personally, the radio harness as everything you need +12 battery, +12 switched, dimmer and ground. Use an inline wire tap to connect.

Ok you can/will do anything you want but here is the warning. I have been an Electrician for over 45 years now whether it be aircraft,commercial or industrial. When circuits are engineered they are for the requirements Voltage,amperage,wire size and fuse or circuit breaker. When you start tapping off of existing circuits the wire size and protection are thrown out the window. It is ALWAYS better to design a new system so you do not burn your truck to the ground.

Dave

 

[glmoore001]

Ok you can/will do anything you want but here is the warning. I have been an Electrician for over 45 years now whether it be aircraft,commercial or industrial. When circuits are engineered they are for the requirements Voltage,amperage,wire size and fuse or circuit breaker. When you start tapping off of existing circuits the wire size and protection are thrown out the window. It is ALWAYS better to design a new system so you do not burn your truck to the ground.

Dave

The next big project is a head unit, speaker upgrade, so there is no use attaching anything here.