M35-M38 Wiring harness interchangeable

Stiknruddr · Post by **Stiknruddr** » Wed Aug 09, 2017 6:55 am

I need a new wiring harness in my M38 have read some previous posts about using a nos M35 or M37 harness and modify. I've studied the early M35/37 wiring diagrams. I see they are similar. Couple of questions...my M38 is a early one with the 2 plug light switch the M35/37 harnesses appear to be single plug thus a need to change the light switch? There are items (especially on the M35 harness) that are not needed, just not use those circuits? Obviously lengths will need to be adjusted which will entail splicing. Are multiple harnesses required i.e. Main, rear, headlight, instrument....I see main and rear ones for sale in the $225 range. Anyone actually done this retrofit? Is the M37 harness easier to work with? My M38 is a runner to carry my M1917 on the pedestal mount not a full restoration. I'm considering using either 12v single wire alternator or 24v....looking at bypassing the mil voltage regulator and splice into the harness. Any advice appreciated!

Post by **wesk** » Wed Aug 09, 2017 8:39 am

You already said that accuracy was not on your agenda. Therefore the two plug light switch is a simple convert to one plug use. On an original 2 plug harness you just move the wires and pins from the small plug to their correct positions on the large plug. In your case you would simply plug and play the single plug onto your two plug switch's large receptacle. It will function just fine. The large light switch plug is the same in all the military harness up to present day Hummers.

If the jeep is already 24 volt you can either use a Delco one wire 24 V alternator or the military one wire 24 volt 60 A alternator, bypass the regulator and enjoy the jeep.

My M35 tractor harness on my M38 only cost me $40 NOS.

I would suggest you first decide on a direction: 12V vs 24V, with or without turn signals, any other accessories you are planning on.

Then shop harnesses. When you see a reasonably priced harness then google the wiring diagram for that vehicle's system and compare it to your needs.

The benchmark for your shopping is that New Repo M38 harness which is over $700.

Stiknruddr · Post by **Stiknruddr** » Wed Aug 09, 2017 4:22 pm

Thanks much. I can handle the differences move the pins etc. any source for a harness at that price? I can make up the headlight taillight harness....ordered some wire and connectors. I found a schematic Wes Knettle drew up showing installation of a alternator, pin jumps, etc. I'm going with 12v for now using a Delco 10si single wire 63 amp double pulley alternator ($57) on eBay. I'll eventually get around to a full restoration and put 24v back on it. It already has a 12v starter, distributor and coil. I see instrument harnesses at Saturn Surplus. I'll post with update....now about that $50 source!

Stiknruddr · Post by **Stiknruddr** » Fri Aug 11, 2017 9:32 pm

Well no solid options so I bought several harnesses off EBay will build my own. Talked to vintage wiring in Maine $760. No go. $125 of harness build one for my needs.

dpcd67 · Post by **dpcd67** » Fri Aug 11, 2017 10:25 pm

I am doing that exact thing right now for my 6-51 M38; it has the two hole firewall panel, but I am using a one socket light switch. I am in the process of taking apart the M35 harness and will use only the wires needed; the extra ones can be used for headlights, etc. I will buy the regulator harness; it is hard to make. Packard connectors for most of it. Total price will be less than 200; 24 volt, generator and regulator.

4x4M38 · Post by **4x4M38** » Sat Aug 12, 2017 6:44 am

Brent Mullins is selling the two plug switches NOS as I recall.

Stiknruddr · Post by **Stiknruddr** » Sat Aug 12, 2017 11:56 am

The M744 harness is real close. Milsurplus on eBay has 2 harnesses for sale. Enough material to work with. One is a M38 headlight harness. The other is a trailer harness with multiple 50 ft 14 guage wire, packard connectors and trailer plug.

dpcd67 · Post by **dpcd67** » Sun Aug 13, 2017 8:51 am

Yes he is selling the two plug light switch but I have no cannon plug to fit it so I am going to one plug.
I un wrapped my M35 harness last night; took an hour to cut off all the tape. Now I will remove all the extraneous wiring like turn signals and others that the M38 doesn't use. Then plan from there. There is enough extra wire to make the headlight harness and others.