Switched power-24/12v help??

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slmanella

New member
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Location
Long Island, NY
Hey guys,
working on a 24/12v conversion for some accessories and I'd like to have this circuit keyed to my ignition switch.
I have a simple 24/12v converter wired to a keyed ignition switch.
Converter is wired to the switch ground and acc legs. Switch off - 0v, Switch on - 24v
No problem there as i have stable 24v into the converter and 12v out. The 12v out goes to a Blue Sea fuse block and powers my 12v devices ... all good.
But, as soon as i shift into gear, whether forward or reverse, the 24v going to the converter drops to 0v. Shift back to neutral and goes back to 24v.
I know i can have constant 24v but the goal is to have a switched circuit.

any thoughts or suggestions are greatly appreciated,

thx
 

Coug

Active member
352
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28
Location
Olympia/WA
I'm not really up to speed on how the ignition is wired, but it sounds like the power you are connected to is wired through the neutral safety switch.
 

papakb

Well-known member
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48
Location
San Jose, Ca
What "switch ground"? Did you mean battery negative? I have to agree with coug, it sounds like you've connected the +24v power to the converter to the neutral start line. You want to pick up power from the 27A lead. This will be hot whenever the truck is running.

Ign switch.jpg
 

slmanella

New member
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1
Location
Long Island, NY
Yes, battery negative on the switch is what i'm currently using. Thanks for the drawing! Since i'm new to the wiring layout could you steer me to the location for 27A?
Your assistance is greatly appreciated,
Steve
 

papakb

Well-known member
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Location
San Jose, Ca
If you haven't already downloaded the free manuals for the HMMWV I'd suggest you do it as soon as possible. 98% of the problems your going to have with the truck are covered there along with simplified flow charts that help you diagnose issues. The wiring diagrams for the vehicles are located in the back of the TM 9 2320-280-20-3 manual. There are a bunch of them so you need to pay attention to the title block for the one your looking at to make sure it's the correct one for your truck. Almost all of them are fairly similar so for generic things like the STE/ICE connector you can use any one of them but be aware that specifics can be different. For example, you won't find an A2 manual much help diagnosing a trans problem in a basic M998.

You'll also see why the 400th copy of the original drawing has become unreadable as Greg pointed out with my 27A - 29A wire number screwup! LOL
:tank:
 
Last edited:

slmanella

New member
19
0
1
Location
Long Island, NY
Follow up post from yesterday:

After reading papakb’s post about 29A i went right back to the master switch and changed a couple things; most importantly where -24v to the converter was going to.
Once i made that change i was good to go.

thx for the help!!
 
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