Headlight relays

timjuhl · Posted: Thu Jul 12, 2012 5:43 am Post subject: Headlight relays

My Jeep was previously converted to 12 volts. The person who did it installed headlight relays controlled by the high / low beam switch to power the bulbs rather than run the wires directly through the light switch.

Personally, I don't think the current draw is such that relays are called for but I thought I'd put it out for discussion.

I am using the multi-position military light selector switch.

Thoughts?
Tim
_________________
Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft

wesk · Posted: Thu Jul 12, 2012 9:32 am Post subject:

The military light switch has a circuit breaker in it. The 12 volt relays should handle the current flow of the 24 volt system which is a lot less however their voltage sensitive coils in their control circuit will probably not.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

jimm · Posted: Thu Jul 12, 2012 3:03 pm Post subject:

Tim,
To clarify, are you keeping the 12V conversion, or converting it back to 24V?
_________________
Jim McKim
1952 M38 son-father project
Slowly turning rusty parts into OD parts

timjuhl · Posted: Thu Jul 12, 2012 5:33 pm Post subject: Headlight relay

At this time I plan to keep it at 12 volts. To do otherwise would be a major job and cost big bucks. It has an alternator and all of the waterproof wiring is long gone.

Tim
_________________
Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft

wesk · Posted: Thu Jul 12, 2012 9:55 pm Post subject:

That throws an entirely different aspect to the issue. The amp draw of the 12 volts lamps is almost twice that of the 24 V lamps. They probably used the relays to carry the higher amp loading from the battery thru the relays to the lamps so only the lower current needed for the control coils in the relays passed thru the military switch . The circuit breaker in the military switch has amp rating a bit lower than the 12 volt lamps.

So if you are leaving it 12 volt and insist on using the GI switch you may wish to leave the relays there. But I would suggest you provide the appropriate amp fuse/CB to protect the lamp high amp wiring for both hi and lo beams.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

timjuhl · Posted: Fri Jul 13, 2012 8:02 am Post subject: Good point

Wes,
Your response makes sense and I do have the relays.... that said, I may still do some testing and determine the actual current draw on the bulbs.

The fellow who installed the relays also put in a civvy headlight switch. I've removed that and installed the GI type - I drove it for awhile before disassembly and connected the light circuit with relays up to the GI switch.

Would you happen to know what current the GI switches were rated at?

Tim
_________________
Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft

Bretto · Member Joined: Nov 24, 2010 Posts: 1390 Location: Orem, UT

I have wired mine up just as yours is set up. I had asked the same question about the current rating of the switch and was told there was no info. I figured the switch would be fine but I do know what the relays are rated at so I added them. I then have a modern fuse panel for all my circuits mounted to the cowl battery box.
Brett
_________________
Brett
'51 M38
PHOTO DIARY OF MY BUILD

wesk · Posted: Fri Jul 13, 2012 8:59 am Post subject:

Tim,

I have never seen a published number even in TM 9-1825E for the Bendix switch. It's safe to assume the number is very close to 15 amps since that is the size circuit breaker used in all early M series that used the original style Bendix/Scintilla light switch.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

timjuhl · Posted: Fri Jul 13, 2012 6:02 pm Post subject: Headlight relays

Good to know. I assume the circuit breaker you refer to is inside the switch and of an auto-reset type. I never knew it was there.

Tim
_________________
Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft

wesk · Posted: Fri Jul 13, 2012 8:30 pm Post subject:

When the Army went from the Bendix rebuildable light switch to the many later vendor throw away switches they also dropped the separate circuit breaker under the dash for the old Bendix light switch. The new switches, throwaways, all have a built in circuit breaker.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

FIFTY2 · Member Joined: Apr 29, 2012 Posts: 1

check out this website, it has all the specs on the switch:

http://pdf.directindustry.com/pdf/esterline-interface-technologies/military-vehicle-light-switch/54730-172551-_2.html

wesk · Posted: Fri Jul 27, 2012 8:21 am Post subject:

That's the specs on the modern push button replacement switch that was developed in the late 1980's and is found in today's Army vehicles.

_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php


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