Wiring question- Unused pigtails

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Ajax MD

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In my M813, there is an unused female pigtail dangling from the dash wiring harness.

The wire is #40, which according to the wiring diagram in the -20, is used for "panel lights." The sketch does seem to indicate a pigtail in the wiring harness at that point.
This would seem to indicate that the pigtail only has power when the panel lights are turned on, which suits my purposes.

I have a small, 24v - 12v converter from Those Military Guys. Rather than hack into the harness at the battery cutoff switch, I'd rather utilize this pigtail. The only thing this converter is ever going to power is my cell phone so the load will be minimal. Is there any reason not to do this?

According to the diagram, there is also an unused male pigtail on wire #27. This wire also seems to serve the Instrument Panel Circuit Breaker. I haven't actually laid eyes on this one. Is it also accessible under the dash? Would this be a better choice?

I appreciate your input.
 

Bill Nutting

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I installed mine behind a switch. This switch allows me to have all of my accessories disconnected while I’m starting the truck. I fused the 24 volt primary of the converter and connected the 12 volt secondary to a fuse block. All of my 12 volt accessories are separately fused. I don’t want to lose all of my accessories to a single fuse blow. You are doing the right thing using a converter instead of half tapping the batteries.
 

Ajax MD

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@Bill Nutting Are you saying that you installed a separate switch or that you tapped into an existing switch?

I'll fuse the converter for sure, but the only thing hanging off the converter will be a USB plug to charge my phone. If my phone isn't plugged in, it's not drawing any power.
 

Bill Nutting

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I connected an in-line 30 amp fuse to the 24 volt battery connection. From the fuse I connected to a high current switch. I then came out of the switch and fed a 24 volt “accessories fuse block. From one of the new 24 volt fuses I fed a 24 to 12 volt converter. I connected the output of the converter to a second fuse block for my 12 volt accessories. By turning off one switch, I kill all of the stuff I have added to the truck. My application would be overkill for one 12 volt cigarette lighter outlet to charge a cell phone. I converted my M934 into a “motor home”. So I have a bunch of 12 volt stuff I’m using. I also have a 24 to 13.8 volt converter that I use to charge a 12 volt battery that runs all the RV stuff ( led lights, water pump, electric breaks for the trailer, 12 volt outlets scattered around for charging stuff etc.) And it charges a battery in my covered trailer for interior lights and a power jack.
What I’m not sure about is the current draw of the converter even with nothing connected to the output. If the 24 volt wire you use to feed the converter goes dead when the trucks power switch is off, then I think you’re good. The problem I had before I installed the switch was leaving something on and draining the 24 volt batteries. I just wanted to make my truck monkey proof because I need that kind of self protection. :)
 

Fanjan

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Michigan
In my M813, there is an unused female pigtail dangling from the dash wiring harness.

The wire is #40, which according to the wiring diagram in the -20, is used for "panel lights." The sketch does seem to indicate a pigtail in the wiring harness at that point.
This would seem to indicate that the pigtail only has power when the panel lights are turned on, which suits my purposes.

I have a small, 24v - 12v converter from Those Military Guys. Rather than hack into the harness at the battery cutoff switch, I'd rather utilize this pigtail. The only thing this converter is ever going to power is my cell phone so the load will be minimal. Is there any reason not to do this?

According to the diagram, there is also an unused male pigtail on wire #27. This wire also seems to serve the Instrument Panel Circuit Breaker. I haven't actually laid eyes on this one. Is it also accessible under the dash? Would this be a better choice?

I appreciate your input.
I also have a pigtail marked J , can’t find where it goes
 

Ajax MD

Well-known member
962
340
63
Location
Mayo, MD
@Fanjan Hmmm... on the wiring diagram, there are some wiring harness sockets/plugs with a "J" but the "J" wire always translates into a numbered wire further down the line. I cannot find an unused pigtail labeled "J."

On an M816, I'm finding some unused "W" pigtails. What kind of truck do you have?
 

Fanjan

New member
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1
Location
Michigan
@Fanjan Hmmm... on the wiring diagram, there are some wiring harness sockets/plugs with a "J" but the "J" wire always translates into a numbered wire further down the line. I cannot find an unused pigtail labeled "J."

On an M816, I'm finding some unused "W" pigtails. What kind of truck do you have?
I have a 1953 M38a1,, it’s a fairly new harness and everything on Hubble connector checks out except J and I also have a L not being used ,, thanks for your help
 

Ajax MD

Well-known member
962
340
63
Location
Mayo, MD
I have a 1953 M38a1,, it’s a fairly new harness and everything on Hubble connector checks out except J and I also have a L not being used ,, thanks for your help
Ah well, that explains it. I'm looking at the diagram for an M809. I'm sure there are several differences.
 

US6x4

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Wenatchee, WA
...According to the diagram, there is also an unused male pigtail on wire #27. This wire also seems to serve the Instrument Panel Circuit Breaker. I haven't actually laid eyes on this one. Is it also accessible under the dash?
I've been looking into wiring details to power a future pyrometer and I found more details on this wire 27. It looks like it's an unused branch of the 5 wire harness connector that can be found on the back of the gauges.
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