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Can someone identify this item on an M151?

Posted: Wed Jan 16, 2019 12:06 pm
by steveperryman
Saw this from another jeep... I have no idea what it is. Any thoughts?

-Steve

Re: Can someone identify this item on an M151?

Posted: Wed Jan 16, 2019 12:17 pm
by markrdje
That's for jump starting the mutt

Re: Can someone identify this item on an M151?

Posted: Wed Jan 16, 2019 12:53 pm
by hambone
That is the slave connection, as Mark stated, it's for jump starting, common on MV's.

Re: Can someone identify this item on an M151?

Posted: Wed Jan 16, 2019 1:58 pm
by W. Winget
An elaboration:
There is a large heavy two wire cable that has a special plug (either one prong or two, with small metal adapters for either end usually carried in the vehicles tool bag) the earlier standard was two prongs (+/-) and NATO came along with a single center (hot +24V) prong, you turned power off on your dead vehicle, and your running vehicle, connected your cable, then started your good vehicle, and finally your dead vehicle.
It was (and is) called a "Slave Cable", and that part you photo'd was called a "Slave Cable Receptacle". You will find them on almost all "M" series vehicles, generators and some earlier 12V variants were made for WWII Cold weather applications (from memory) They are now generally only 24Volts, avoiding the jumper cable sparks around a potentially off-gassing battery that could blow up.
It's my understanding the Telsa models use a similar (but smart) cable for charging now.
Don't stick anything in it!


I have seen museum and large group collectors carry two 12V Gel batteries in an ammo can (24V) with slave cable pigtail plugged into their MUTTs to basically eliminate the need for constantly working on vehicle batteries in their collection, but just don't disconnect it while the vehicle is running, it may damage the generator/altenator if there are no batteries in the system.

Slave Cables tend to be around 20 feet in length, longer in Armor units because they reach inside the vehicles, but they are ALL heavy and cumbersome.
V/R W Winget
PS: the star should not have been painted under it, even if added to a vehicle the motorpool would have touched up the paint.

Re: Can someone identify this item on an M151?

Posted: Fri Jan 18, 2019 11:49 am
by Kurt Lesser
Tesla used the newer "Nato" style coaxial connector on some of their earlier vehicles but chose not to go with it because of the expense of the connector and there were some safety concerns about exposed contacts. I have one with a nice anodized red cover that says Tesla on it.

I wanted to comment on your jump start procedure. I have always told people to have both vehicles turned off when connecting them together and then try starting the dead vehicle with the slaving vehicle turned off. This is because if the slaving vehicle is running when the slaved vehicle starts drawing current attempting to start it can draw more than the generating system can output and it can damage the alternator/generator. Alternator diodes are usually the first thing to fail.

Re: Can someone identify this item on an M151?

Posted: Fri Jan 18, 2019 12:00 pm
by W. Winget
Kurt I have always had the vehicle running to protect the alternator, as it's energized producing current at the time of the heavy amperage draw, thereby helping to keep both your battery and charging system up.
Go figure, another topic of difference, now an electrical engineer will correct one or both of us :wink:
V/R W Winget

Step e below:
One example from TM 9-2320-280-10 (Just a the first crap I googled not saying It's right or wrong... :wink: )

2-23. SLAVE STARTING OPERATION
a. Position slaving vehicle and disabled vehicle close enough for cable hookup.
b. Stop slaving vehicle engine.
NOTE Vehicles with kits 5705623 and 5705624 and serial numbers 100,000 and above are equipped with screw-on covers.
c. Remove cover from slave receptacle of disabled vehicle and slaving vehicle.
WARNING Ensure all battery cables in disabled vehicle are properly connected before connecting slave cable. Damage to batteries,cables, or serious injury to personnel may result from improperly connected batteries.
CAUTION Use a twisting motion when installing slave cable to the receptacle.Forcefully pushing the cable onto the receptacle may cause damage to the receptacle mount.NOTE Ensure all electrical switches in both vehicles are turned off.
d. Connect slave cable to the slave receptacle of both vehicles.
e. Start slaving vehicle engine.
f. Start disabled vehicle engine.
CAUTION
Use a twisting motion when disconnecting slave cable from the
receptacle. Forcefully pulling the cable from the receptacle may cause damage to the receptacle mount.
g. After engine starts, disconnect slave cable from both vehicles.
NOTE• Screw-on type covers must be fully tightened to ensure a proper seal.
• For ease of removal, apply hand cleaner (Appendix D, Item 11)on the inside of the cover before installing receptacle covers.
h. Install receptacle covers on both vehicles.
i. Clean and stow slave cable.

Re: Can someone identify this item on an M151?

Posted: Thu Jan 31, 2019 1:57 pm
by steveperryman
Hi All, wanted to express my thanks for all the info that flows through this site. My passion for restoring these jeeps would have been snuffed out a while ago if not for the guidance and support of you guys. Thanks so much....

Re: Can someone identify this item on an M151?

Posted: Wed Feb 06, 2019 10:20 am
by mdainsd
The slaving vehicle should be running and at a high idle when attempting to start the disabled vehicle. Better yet, if time permits, allow the slaving vehicle to run at high idle for several minutes before attempting to start the disabled vehicle. This gets an initial charge in the dead batteries that greatly increases the success of jumping. Ive had success jumping an M60 with a M37 using this method more than once :wink:

Slaving from a vehicle that is off results in less voltage available to the disabled vehicle for starting and runs the risk of making two disabled vehicles if the slaving vehicles batteries get too discharged in the rescue attempt.

The alternator would only be harmed if somehow the slaving system got shorted. The alternator takes care of its self for over current conditions.

Re: Can someone identify this item on an M151?

Posted: Wed Feb 06, 2019 6:20 pm
by Rickf
Correct, The alternator will only put out it's maximum regulated current, no matter how much is being drawn from the batteries. And that is a key part of the equation, make sure to always jump from the batteries and never from the alternator terminal! I have seen that done several times and every time the results were bad.