12V supply in cab 923A2

[todds112]

I just downloaded the P2P program for the 939 and spent hours just browsing all the components and diagrams, what a cool program!

Anyway, I noticed there appears to be a 12 volt supply that goes to the heater low setting circuit (569A). Correct me if I'm wrong, but it looks light the circuit breaker on the right is 12v and only services that low setting on the heater. Could I put one of those "Y" connectors coming off the breaker and attach a common 12v power plug there for a GPS, etc?

 

[dmetalmiki]

If in doubt just run a possitive and negative from the FIRST battery for 12 volts. All my 12V accessories are run thus.

 

[Alexsha]

I've got a 24V->12V converter. My plan is to mount it inside the battery compartment and put a few 12V plugs on the box wall as well as a couple 5V USB plugs. That way I'm not draining the batteries unevenly.

 

[1 Patriot-of-many]

Sounds like a good plan to me. Many have said attaching to one battery isn't a good idea.

 

[todds112]

It looks like on the diagram that's the way it is factory wired. That 569A circuit runs from one of the batteries, to the main power switch, then to the circuit breaker, fan switch and finally the fan. Seems odd they would run a special circuit just for the low fan setting, even has its own circuit breaker. I don't see anything else (on the diagram) it goes to, though. Seems overly complicated compared to the simple resistor in the M35a2. I would only be powering a GPS or phone charger, not worried about uneven draw on the batteries. I'll run it after the breaker and put a small inline fuse on the lead to the outlet.

 

[Alexsha]

I don't get why they run 12v for the fan either. I was thinking of running that 12v line through the converter as well.

 

[bchauvette]

This is exactly what I did to power the cell phone and GPS. The additional unbalance compared to a heater motor is negligible. My thinking is that even though we've seen some bonner engineering the engineers must know something and after over 25 years of in service I don't think there is a thread titled "12V blower motor circuit burnt out my battery".

 

[Suprman]

I believe the 12v fan feed was for the low speed setting. None of my trucks have had this hooked up though. I use power converters for 12v switched on with a relay after I start the truck. I have new 100 amp converters in the classifieds.

 

[Plugugly]

I bought this http://www.amazon.com/gp/product/B00HHT9FL2/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1 adapter to power my phone and other stuff, it says it's good for 24v in and 12v out. I haven't installed it yet, and am not sure I'm going to connect to 24v. Once I lop off the plug and set it up to hard wire to the battery, I may wire it to 24v and check the output just to see if it smokes, but I'm not really interested in trusting my smart phone to it.

 

[Alexsha]

I've got a samlex sdc-20 converter. Should be plenty. 100amps seems like over-overkill.

 

[Swamp Donkey]

I ran 24v power out the bottom of the battery box, under the cab and through the firewall to get dedicated power to the dash area. The fused 8 gauge cable then feeds 2 fuse blocks. The 24v block feeds directly off the cable. The 12v block feeds from a converter connected to a fused leg of the 24v block.

The converter is a solid state and waterproof unit rated for 20A, which is more than adequate for standard accessories. It was around $20 on eBay. I mounted it to the top of the dog house under the dash.

Getting dedicated power to the dash has made wiring in lights and such much simpler, instead of pulling power from the battery box. Adding future accessories will be much easier too. Everything is fused and neatly organized down by my right knee. You can see the little converter box on top of the dog house in the picture.

This picture was during installation. There's a few less spots now and everything has been wire loomed.

 

[todds112]

I ran 24v power out the bottom of the battery box, under the cab and through the firewall to get dedicated power to the dash area. The fused 8 gauge cable then feeds 2 fuse blocks. The 24v block feeds directly off the cable. The 12v block feeds from a converter connected to a fused leg of the 24v block.

The converter is a solid state and waterproof unit rated for 20A, which is more than adequate for standard accessories. It was around $20 on eBay. I mounted it to the top of the dog house under the dash.

Getting dedicated power to the dash has made wiring in lights and such much simpler, instead of pulling power from the battery box. Adding future accessories will be much easier too. Everything is fused and neatly organized down by my right knee. You can see the little converter box on top of the dog house in the picture.

This picture was during installation. There's a few less spots now and everything has been wire loomed.

View attachment 531104

That looks very nice. I did something similar to Jeep years ago to hook up all the extras I added to it. Of course it was just a straight 12V set up without the converter. Made adding accessories much easier.