Guys: I'm redoing a 1952 Willys stake bed truck, see attached, and I am having trouble with the temperature gauge. The truck starts and runs well, but after a few minutes the temp gauge pegs to hot. I have replaced the water pump, thermostat, 6 volt sending unit (it is still a 6 volt system), and the radiator. It still shows hot, but I have had two inferred temperature guns on it and it never gets above 190 degrees, even after running for an extended time at the stand still. My parts book shows what is called a voltage regulator that mounts on the back of the instrument cluster and the output side goes to both the gas gauge and the temperature gauge. I put in 5 gallon of gas after cleaning the lines and replacing the fuel tank, and the gas gauge showed about 1/2 full. I think this is also high for a 15 gallon tank. I tested the voltage regulator on the gauge cluster and I get the same reading in as out, all above 8 volts. I'm thinking this device is not working properly, any thoughts? Thanks.
LarrBeard is our resident electrical genius. He has done some research and has documented what he found out on his '48 truck. The following link is what he found on his;
GMWillys is blowing smoke at you – I’m not a genius, I’ve just made enough mistakes to know where to look for the correct answer (well, at least sometimes).
The short answer – Yep, the regulator is toast. 8-volts in and 8-volts out says it isn’t doing any regulating.
Here is a good place for instrument cluster information:
His description concerns me since he calls it out for “12-volt 1946 to 1956 use”. You should call him and get more information before you drop $65 + shipping for a unit that might not work.
Many car manufacturers by 1952 had incorporated instrument cluster regulators in their dashes. These regulators brought the nominal 6-volt system (really closer to 7-volts) down to a lower voltage to keep gauges from wandering around as the battery voltage changed. The regulator was a thermal device, with a bi-metal strip that controlled a set of contacts. With the contacts closed, the full battery voltage was applied, when the contacts were open, zero volts were applied. The gauges had a slow response time so they would respond to the average of the voltage applied. If you applied 7 volts about 70% of the time and 0-volts 30% of the time the average voltage is about 5-volts which is where most gauges actually ran. This sounds pretty crude, but it worked. If the battery voltage went up, the contacts heated up quicker and the “on-time” went down – reducing the average voltage. And – if battery voltage went down, the contacts stayed closed longer – bringing up the average.
Here is another option that would probably be a close replacement:
This is a “relay type” regulator like the original thermal regulator. Many of the “new solid state” regulators are just series resistors that don’t do as good a job of regulating; they just reduce the voltage and don’t really regulate – so beware.
But, I have another concern. You mentioned that the regulator had about 8-volts in and out. If 8-volts is where the electrical system is running, that’s pretty high if the battery has topped off its charge. A constant 8-volts on a 6-volt system will give a lot shorter battery life as well as cause issues with lamps and lights. I’d check the voltage at the battery terminals with a pretty good voltmeter and if it really is 8-volts, I’d look for charging system issues (most likely a defective voltage regulator – easy fix).
Let us know what you find – we’re always curious. Oh, by the way – Nice Truck. That's a pretty fancy front bumper for a farm truck. Those were more common on the fancier wagons. Is there a family history for it or did it just show up looking for a home?
What a complicated setup for a gauge. You have to wonder why they didn't stick with mechanical. I remember all you have gone through with that gauge cluster Larry, you definitely have them figured out!
Thanks for the information. I have a used instrument cluster with the attached voltage regulator, I will install that device and hope for the best. The voltage to the battery may be high because this vehicle has not been run much and started many times. I did not want to run it too much because of the hot gauge issue. I got it from a woman in upstate New York who had it in a barn for 30 years. She purchased it from a small town in New York where it was used by the road maintenance manager. It was missing the rear three metal stakes, so I had some fabricated by a local welder. It also had some rust, but the body was pretty straight. The rest is all original, it was originally a green, but the guy I am brining this one back to life for wanted it flat black.
"I have a used instrument cluster with the attached voltage regulator, I will install that device... "
Hey, give it a shot. Some varieties of regulator used the tab on the case for a ground, so don't just hook up two leads. If the little bi-metal strip is going open and closed, it may give you a funny reading on a meter. On a digital,the numbers will jump around a lot. On a good old fashioned analog meter, the needle may quiver and jump. That is a good reading. Of course, an oscilloscope would give you a picture of exactly what is happening - but that is overkill even for me.
It was interesting to see the interior. By '52, the pushbutton doors had given way to the conventional handles.
Guys: After thinking more about the comments on this page, I did a test. If I am getting about 8 volts to the temp gauge when the truck is running, and with a 6 volt battery, I should only get a little over 6 volts with the key to on, but not running. I started the truck and ran it until the temp gauge pegged to hot and then turned the truck off, just long enough for the temp gauge to return to the cold position. Then I turned the key on, but did not start the engine. The temp gauge rose to just above the 1/2 way mark. So with 8 volts to the gauge the gauge shows hot, and with 6 volts to the gauge it shows about 1/2. This confirms to me that the voltage regulator on the back of the instrument cluster is not working. Now, I only need to replace that regulator with a good. Thanks again for all your help.
I found a discussion online about this instrument cluster voltage regulator. The discussion included a test procedure. It said the ign to case should read 42 ohms, and 0 ohms ign to output. The regulator I have to be used as a replacement regulator to the one not working reads 42.7 ohms ign to case, and 7 ohms ign to output. I think this should work for my application. Thanks.
[I]"The regulator I have to be used as a replacement regulator to the one not working reads 42.7 ohms ign to case, and 7 ohms ign to output."[/I
This is probably more than you want to know:
The attached picture is a diagram of what is probably inside your voltage reducer. (The IGN to output probably should be drawn as a normally closed set of contacts, but ...). There is a bi-metal strip wound with a heater wire. There are two sets of contacts on the bi-metal strip. One set of contacts controls power to the heater. When the strip is cold, the heater turns on, warms up the strip and as the strip bends, it opens the contacts. Once the strip bends and the switch contacts open, the heater cools off, the strip returns to its original position and the process repeats. This heater circuit is the 40-ohm circuit you see from IGN to CASE.
The bi-metal strip has a second set of switch contacts that connect the IGN terminal to the other contact on the regulator. These contacts are the contacts that open and close to produce the “average” voltage to the instrument cluster.
The procedure you found to test the regulator calls out zero-ohms from IGN to the regulated output – a closed set of switch contacts. If you are reading 7-ohms across those contacts, they are damaged. That resistance will add 7-ohms to the resistance of the gauges that are sensing temperature, fuel level and oil pressure. The problem isn’t so much that the readings will be off a bit – but the points will eventually overheat and fail. They will probably weld themselves together.
If you can open up the bad unit – open it up and look at how the contact points are arranged. I suspect that the bad unit has welded points. If you can see how to get to the points, open up the good unit and give the points a good cleaning.
Or – just try the old regulator and see how it goes …..
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