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I have been trying to aquire all of the guages I need for my M-38 with Douglas connectors... I finally got the voltmeter to complete my set. During this process I found a way to test to see if the guages work with out putting them in the jeep.

I take a pair of 12 volt jell cell batteries and hook them together in series (+ to -) then place the ground on the connector with the slots in it (-). Next carefully tap the positive lead to the connector with the tabs on it (+). This should cause the guage to go full scale...

I have tested fuel, oil pressure and of course volt meter this way... I tried to test the temprature guage the same way and it would not work. Upon further examination ( I opened the guage up carefully to clean the lenses and take the bezels off for painting); I found one of the coils had a broken wire. I do not feel as if I wil be able to repair this as it is too fine for my eyes to see.

I now have a question, has anyone taken a packard connector guage apart and tried to mount it in a douglas connector guage? I mean just swap the cases... If so please let me know.

With the temp guage being bad it means I now need to find another one to replace it with...

Comments, please...

That wasn't one of those earlier gages that needed a resistor between it and the 24 volts? If so then the staright 24 volt shot ate the wire in the temp gage and as Buzz said you were lucky on the other two. I would not apply 24 volts directly to any dash gages except the voltmeter.

Try these guys: http://www.gaugeguys.com/

I would like to re-open this topic.

On early gauges Wes you said there was a resistor in series with the voltage supply. Do you know what value of resisitance is used when checking a gauge.

I have new 0-120 psi gauge. Is an external resistor required in the circuit?
The wiring diagram doesn't show a resistor.

Ken,

The resistor is part of the gauge. It comes off the back in a black pipe looking tube with the douglass conector at the end.

See ORD 9 electrical section photo of the gauges and you will see it on the back side.

I have one that fell apart and it says on the side of the resistor :

RES 95

Ryan, The new gauge that I received doesn't have a resistor on it. The box it came in is dated 12/72

Today I was checking a take off 0-120psi sending unit applying air pressure and with ohm meter connected to the gauge terminals I watched ohm meter change when pressure was applied. I guess I can assume the sender is good.

Now checking sending unit and a new gauge together.

I connect negative 24V power to case of sending unit, connect a wire from sender terminal to negative terminal of gauge, connect the other gauge +terminal to positive power. Apply pressure to sending unit. The gauge does not register any pressure. Reverse polairty, still nothing.

Next with a ignition resistor, (a couple of ohms) I connected resistor to neg, power, connected other side of resistor to negative term. on gauge, and then breifly touched the positive term of gauge to positive of power supply. I observe no meter movement on gauge.

Next I put the ohm meter (x1 scale) to terminals of gauge and observe some ohm meter movement on high end of resistance scale. say 100 ohms. It isn't a precision meter but does work.
I don't know if I can determine here the the meter winding is good or not.

Ken,

Wes can better answer the technical side of the electrical gauges than I could.

Have you read thru and applied the 24 volt gauge trouble shooting article that Bob Westerman provided us?

It is on the yahoo storage site, but will be on the new file section (called downloads). The new website storage and photo gallery/homepage, etc. should be up in a few days and you will be able to download it there.

Bob also has it on his website at: http://www.cj3a.info/

Ryan, I see the object on the back of the gage in the photo. I did not know what that was before.

I looked at Bob's instructions on testing the sender and my sender passes test.

Bob's instruction clearly say that gage case must be grounded for it to function. something that I did not do.

I will make a note of that on my diagram.

I guess his instruction assume the resistor is on the gage. doesn't speak of any resistors in the circuit.

I will have to find some resistors. I'll go to radio shack and pick up some resistors to use temporarily on a bench test. maybe tomorrow. Hopefully the gauge is still good.

With the date you gave on the guage, 12/72 no resistor is needed... thiose resistors were needed on the early models... (Probably a holdover from the MB/GPW days?)

I just installed mine straight away and all is fine...

Hope this helps...

Ok Hal I'll try bench test again tomorrow with out the resistor, and make sure case is grounded.

Ken,

Hal is right. You shouldn't need an external resistor with the later gauges.

Good luck tomorrow and let us know how it went.

Ken,
The troubleshooting instructions do assume that the resisitor is in place on the gauge. I read somewhere that the early gauges were actually 6V units so they needed the resistor.

Back to the original positing in June, my M38 temp gauge did not operate. It also had a broken wire on the end of one of the coils. Looked like maybe they used acid core solder when it was made and it finally corroded through the wire. I did manage to unwind one turn from the coil and resolder the wire back on the terminal. It's still working, knock on wood.

I connected the gauge and sender to power, made sure gage and sender case were connected to negative supply. Needle on gauge comes active, Applied pressure to sender and observe that gage needle responds to pressure. I'm not sure if the gage on air supply regulator is correct or calibrated, but it tells me gage is good and responds to pressure.

Ken

I realize that this is an old thread, but I am going to switch my Amp gauage to a Volt gauge. I know that I will have to buy a 5 wire spider harness and connect the spare #27 wire to the Volt meter. The #8 and #9 wires for the Amp gauge will have to be taped off. Is that all I need to do - hook up the #27 wire to the Volt gauge? What is the other stud/nut on the back of the Volt gauge for?

I finally got all of my gauges working this week - my Fuel and Temp gauages weren't working. I used the troubleshooting guide to hunt down the problem. The Temp sending unit was bad, and I had a bad ground, causing the Fuel gauge to not work. I also went ahead and ran an extra ground wire (with crimped ring terminals on each end) from the speedometer to the firewall. I cleaned all of the paint off of the firewall to make a good ground point. I ran a 3/16" bolt through the firewall and secured it with a locknut. I can use this bolt for another ground point if necessary.