dimmer switch wiring

4x4M38 · Post by **4x4M38** » Tue Feb 24, 2015 1:42 pm

I have a question about dimmer switches and wiring on M38's and M38A1's.

I have seen two different versions of the dimmer switch supposedly for the M38/A1.

One I have seen and have in hand has Douglas connectors and has two wires with connectors to the switch, and the third wire is hard wired into the switch and is a ground.

The second switch I have seen has Packard connectors and does not have a ground wire but has instead three wires with connectors to the switch.

Looking at wiring diagrams I do not see how the first switch would work unless the low beam headlamp is lit all the time, and actuating the switch just turns on the high beam. The wiring diagrams do not support this however.

The second switch is easily explained looking at the wiring diagrams. Three wires. One power in, one low beam, and one split high beam/high beam dash light.

Any ideas as to what;s up with that first switch?

Thanks.

Kendall · Post by **Kendall** » Tue Feb 24, 2015 2:01 pm

Actually if you look at the wiring diagram you will note wires 16, 17, and 18 associated with the dimmer switch. According to Table IV under paragraph 163 of TM 9-8012, 16 is power from the light switch, 17 is to the high beam indicator light on the dash and headlight (it is the wire coming from the dimmer switch and should have a double Douglas connector on it), and 18 is dimmer switch to headlight. Note, none of these are ground wires.
Kendall

4x4M38 · Post by **4x4M38** » Tue Feb 24, 2015 3:09 pm

I agree. The wiring is pretty straightforward.

However, most of the takeoff or used units I've seen with Douglas connectors have one wire that is pretty much stripped of insulation, where the other two usually are fairly intact. I am looking at the one I took apart that was not working and it is labeled BAT, Hd L, and H.

So it looks like one of the wires seems to take more abuse than the other two and gets ripped of insulation. Wonder if it is in a worse location? The BAT and one leg of the H wire both go back up to the firewall, and the other two wires go to the headlights. Weird.

Maybe 17 gets shredded because of that larger, double connector.

Thanks for helping me clear that up.

Bretto · Post by **Bretto** » Tue Feb 24, 2015 3:31 pm

I can't say what that 1st switch would be, maybe an on/off? What do the terminals read with a VOM when you toggle it?

The floor headlight switch it not technically a dimmer, it just directs battery to either the high or low beam filaments. And to do this, it needs 3 leads like the 2nd one you have.

Kendall · Post by **Kendall** » Tue Feb 24, 2015 4:14 pm

Does your switch look like the one pictured in Ryan's book on page 94? Because the dimmer switches I have seen just have one wire plus two Douglas connectors afixed to the switch.
Kendall

chrisk · Post by **chrisk** » Wed Feb 25, 2015 5:27 am

Hi Brian,
The dimmer switch with 2 fixed Douglass connectors and 1 wire:
-Douglass connector Male is the wiring # 18, is the Low Beam.
-Douglass connector Female is the wiring #16, goes to the Light Switch # "'D".
-the wire have the #17 is the High Beam.
This switch is the ORDN.PART #7728788.

The other dimmer switch with the Packard connectors:
-Packard connector with "L" numbered in bakelite, is the Low Beam #18.
-Packard connector with "H" numbered in bakelite, is the High Beam #17
-and the third Packard is the #16, goes to the Light Switch # "D".
This switch is the ORDN.PART #8396186 resp. MS-5300-1, #4164.
Chris[/b][/i]

skyjeep50 · Post by **skyjeep50** » Wed Feb 25, 2015 8:42 am

Just replaced the dimmer switch in my M38 - had been a civvy switch modified to work in place of the original Douglas switch. I used a take-out switch that had been used but was still in fairly good shape. The loose wire on take-outs can be in bad condition - the rubber insulation drys out and flakes off. In fact, that was the condition of most of the wiring system in my M38 and why I replaced the whole wiring bundle. New (old) switch plugged right in and works great. In several other areas I have also used gauges and senders with Packard connectors. They work just fine as well.