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1939 1.5 ton wiring question
#1416793 Tue Jul 13 2021 01:37 AM
Joined: Sep 2018
Posts: 21
I have been attempting to rewire a 1939 1.5 ton truck that was just recently given to me by my father. I have been using a kit I bought from Chevs of the 40's, it is for the original generator. The instructions are sort of vague and I am not sure where I am supposed to connect the big wire from the Ammeter to the generator, this was a fire truck for part of its life and it has what looks like a condenser for a radio on the generator. when I attached the wire to this, the ammeter read discharge even with the key off. There is what also looks like a voltage regulator on the firewall that the instructions do not mention. I have very little experience with wiring and the lack of color coordination or markings on gauges is really hampering my progress. Any help or tips are greatly appreciated.

Attached Files
Generator Picture.jpg (208.53 KB, 194 downloads)
Voltage regulator.jpg (245.26 KB, 193 downloads)

1939 Chevy 1 1/2 ton with 216
Re: 1939 1.5 ton wiring question
Libby007 #1416820 Tue Jul 13 2021 12:41 PM
Joined: Feb 2019
Posts: 2,099
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Here is a link for a wiring diagram from a 1941 Chevrolet Shop Manual that should be close to what you have.

Courtesy of Keith Harty and his fabulous website.

Last edited by Phak1; Tue Jul 13 2021 12:45 PM.


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Re: 1939 1.5 ton wiring question
Libby007 #1416838 Tue Jul 13 2021 02:59 PM
Joined: Apr 2007
Posts: 891
I have more questions than answers;
1. Is that a condenser on the generator or a cut out relay?
2. Is your new wiring harness designed for a later voltage regulator (with three contacts for voltage regulator, cut out relay and current regulator, like that shown in the wiring diagram linked above)? Or is it designed for just a cut out relay like you would have for a 1937 truck?
3. Is that a headlight relay in your second picture on the firewall (and not a voltage regulator)?
This time period was one of transition from having just a cut out relay (1937) to voltage regulator with cut out (1938) to addition of a current regulator (1941, I think). So, no telling what you truck might have in terms of modifications at this point. You need to figure out what you have on your truck, and what your new harness is designed for.

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix
Re: 1939 1.5 ton wiring question
Libby007 #1416843 Tue Jul 13 2021 03:41 PM
Joined: Mar 2010
Posts: 610
I hope I'm not butting-in on the discussion.

Normally, one wire on the field terminal and one wire on the armature.
With an add-on noise suppression capacitor, add wire to armature terminal.
The capacitor body is ground and is grounded through the clamp and body of the generator.

From the picture it looks like one terminal is grounded. Doesn't look right to me.

One way to check if the unknown device is a cut-out or capacitor, remove wires and measure resistance (ohms) with meter.
A cut-out will measure 0 resistance. If using a digital meter nearly 0 resistance.
A capacitor will measure low resistance (may need an analog voltmeter) as it begins charging (meter deflection or change) and measure high resistance when charged (if the capacitor is not dead).

Re: 1939 1.5 ton wiring question
Libby007 #1416856 Tue Jul 13 2021 05:08 PM
Joined: May 2005
Posts: 8,335
Sir Searchalot
Libby, by maintaining all those old electrical parts, you are in for your 19th nervous breakdown. As you can see, it's already getting way too complicated trying to figure out and use parts that are probably burnt out, or will be burnt out, and then not available. Their performance and reliability is lousy. You are going to get really confused, especially if wiring is not your thing.

I don't know your goal as far as originality. I hope it does not include wiring. I can help you and save you a whole lot of trouble if you are willing to go 12V. It's simple and gets rid of all those goofy components and wires. Old wiring techniques/electrical systems are nothing to hang onto. Bad idea.

Also: What is the part number of the harness you bought? What motor is in it now?

I see you are putting in a 1958 235 in your 1946. That is a 12V era motor with a 12V starter. So you must already know about 12V conversion?????????

The 1939 wiring diagram on the Hardy site shows two "components" on/near the generator. Labeled "Field resistance" and "circuit breaker". Also shown in 37 but not 40. Some diagrams show a "Polarity Reversing Switch". All a bunch of clap trap.

Watch out for careful drivers!!!
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Re: 1939 1.5 ton wiring question
Libby007 #1416874 Tue Jul 13 2021 07:34 PM
Joined: Mar 2010
Posts: 610
Well I stepped in and went right over my head on this topic.
Did a little reading on 1937-8-9 Delco generators.
1 post, 2 post and 3 post generators. Come back?
Early generators used a cut-out (poster's second picture).
Add to this GM rebuilt generators had another part number.
My head is starting to hurt.
1939 was a design transition year. 1941 all production goes for WW2.
Someone with historical knowledge and experience is needed.

I'm satisfied with the 6 volt system in my 55 1st truck.
I can still get the correct parts I need.
If you are not going 100% original and want to stay with 6 volts, I would definitely update the generator and regulator to the newer 50's design.

Re: 1939 1.5 ton wiring question
Libby007 #1416878 Tue Jul 13 2021 07:42 PM
Joined: Dec 2018
Posts: 781
Libby007 Unless your a purist a 1-wire alternator is a good way to go splice bat. and arm. wires at the regulator change bulbs if not done already,gas gauge resistor,heater motor resistors (takes2 )use your fused heater switch. Only trouble may be alternator kinda hard to prime because of low R.P.M. Use as small an alternator pulley as is practical, ammeter should show charge work good. Bartimos is right get it so you can drive it not work on it all the time !!! oop change coils !!

Re: 1939 1.5 ton wiring question
Libby007 #1416879 Tue Jul 13 2021 07:48 PM
Joined: Dec 2018
Posts: 781
Libby 007 get heater resistors at NAPA put after your heater switch

Re: 1939 1.5 ton wiring question
Libby007 #1416942 Wed Jul 14 2021 02:22 PM
Joined: Sep 2018
Posts: 21
Thanks for all the replies, I will respond to what I can right now.
The motor is the original 216 on a 6V system.
I am going to take that condenser off, it seems like it doesn't belong.
All of the gauges worked prior to this but the cloth sheathing was badly degraded
I am trying to work with what I have for right now to keep cost down, will probably upgrade to 12v in the future but thats aways off.
Here is the item number for my harness from chevs 1865315P 37^39.
Looks like the harness is for a cutout but could I put in a voltage regulater off a '46? I figure I would need to add a couple wires.
It mentions a field resistance coil on the generator, not sure where that is.
Also this harness has no fuses, i will have to splice in some, what size fuse for the ammeter and does it go on the post on the charging side of the gauge or the opposite? I have it on the posi side right now

I appreciate all the help, I don't have very much experience with wiring and this has been the best place to get answers from those who have done it before.

Attached Files
20210714_090224.jpg (125.21 KB, 111 downloads)

1939 Chevy 1 1/2 ton with 216
Re: 1939 1.5 ton wiring question
Libby007 #1417004 Wed Jul 14 2021 11:49 PM
Joined: Sep 2018
Posts: 21
quick update, that box on the firewall is not a voltage regulator, it is indeed the generator cut out, looks like it was moved there because of the condenser.

1939 Chevy 1 1/2 ton with 216
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