Bench Testing

[390xlt]

I there a good way to bench test the gauges? I figured out the hard way that just sending positive though the voltage stabilizer then to one side of the gauge and grounding the other is not the way to go about it

[1972hiboy]

Good question, anything can be done, first you would have to get the whole thing lit up by suppling power to the IPVR so it can pulse out its 5volts to the gauges. then you would have to input each gauge / circuit individually to test according to their respective ohm sweep. If you knew all the values for each each gauge and it was practical for you to spend the time to set it up for bench testing then sure. If you are a guy working in a shop you prob wouldn't bother,

[390xlt]

Getting power to the ipvr isn’t a problem (assuming it gets 12v) and I don’t think determining the correct ohm rating for each gauge should be too hard. (Of course, I’m assuming that information is fairly readily available online; I haven’t checked.) I think it should be okay even if I don’t have the exact right figures, as I’m just trying to make sure the gauges move, not determine their accuracy. My main problems are 1) how to create a jumper wire (or whatever) with something close to the correct resistance, and 2) how to determine which jumper to hook up to which post on the gauge. I’ve made a lot of assumptions up to this point, and even a few just in this question, so please don’t hesitate to let me know if I’m missing something, obvious or otherwise

[zgerbic]

I described a tester for gauges just some time back at this link:
http://www.fordification.com/forum/view ... =8&t=96729
It has all the right resistance values.

If you are testing out of the truck, you need a 5.4V power supply to connect to the positive side of the gauge to supply power instead of the truck dash voltage regulator. Otherwise it is the same as described in the link. You may be able to find a 5V to 5.2V power supply by using a USB charger with at least a 1A rating. Measure it with a voltmeter to see how close to 5V it is. A little off and the gauge will read just a little high/low.

So the loop of wiring will look like this.
1. Power supply + to the gauge terminal that the truck would supply power to from the dash voltage regulator (might be marked +).
2. Gauge sensor pickup terminal to the test switch.
3. Test switch back to the power supply negative terminal.

That is all there is to it. Just flip the switch through its positions and the gauge needle should roughly line up with the gauge markings if the gauge is ok. If it doesn't line up then the gauge is a bit out of calibration. If the gauge reads ok with this test, then the problem is elsewhere in the truck. Usually it is wiring/grounding or the sensor is bad/wrong part (common with replacement temp senders). It could, but less likely, be the dash voltage regulator. You can tell if the gauges test out ok and all gauges read high or all read low.

Regards

[zgerbic]

Keep in mind, you cannot test the dash voltage regulator with a voltmeter.

It is a primitive design that just switches the voltage to the gauges on and off at a rate that on average, due to the slow movement of the meter needles, averages about 5.4VDC. A voltmeter will have a reading that jumps around. If an analog meter the needle should swing back and forth. If a digital meter, it is harder to tell but the voltage readings should go up and down.

Regardless, the only way to test a dash voltage regulator is to make sure you have a reasonably calibrated gauge and a test resistance that matches the "full" or "hot" mark at full scale. If the gauge does not read on the mark with a good gauge and correct resistance (10 ohms), then the dash regulator is likely bad.

Regards

[390xlt]

Since I don't have a 5.4v power supply, is there any reason I can't run 12v to the regulator and then run jumpers from there?

[zgerbic]

No reason you can't, just a bit inconvenient. If you are fine with the gauges reading a little low you could just use a USB power supply which is about 5V to 5.1V. The gauges will read about 5% low which is a needle width or so to the left, assuming the gauges are actually ok.

With a known 5.4V source and the resistor values, you can be sure the gauges are working and are still close to calibrated.

Using a dash voltage regulator and the resistor values, if the gauges read right then the gauges and regulator are both ok. If the gauges all read high or all read low then the regulator is probably a bit off any may need replacing. If one gauge reads right and another reads wrong then the regulator is probably ok and just one gauge is out of calibration.

It sound like you just want to get a general idea if the gauges are ok so I would suggest either the dash regulator or a USB supply, and connect a 10 ohm resistor in place of the sensor. If the gauge reads close to the right-most mark, it is probably ok.

[390xlt]

This might be a stupid question, but how would I go about hooking up a USB charger to jumpers? As you surmised, I'm not concerned with the gauges being super accurate; I just want to make sure they needles move in approximate relation to what's happening under the hood (or behind the seat, as the case may be).

[zgerbic]

No such thing as a stupid question, just stupid for not asking and learning something new.

You are testing the gauges on a workbench. In order to get the voltage to some jumpers/connections you would have to cut a USB cable and get the wires exposed, and then find the + and - wires.

I thought of an alternative...
There are lots of ways to find other voltages and resistances to do the tests.

You can use a 12V battery as the power source if you change the resistors used for full and empty. This will give you the same result.
Just don' t try using a 12V battery with the existing sensors or you may end up with a "permanent empty" reading on the gauges from being burned out.

A 5V source with a 10 ohm resistor will give you a full reading. With 73 ohms you will get an empty reading.

A 12V source with a 43 ohm, 2W, resistor will give you a full reading. With a 182 ohms, 1W, resistor you will get an empty reading.

Since you are just looking for an approximate test to assure the gauges are good you can get by with a 47 ohm resistor (a standard size) for full, and four 47 ohm resistors in series (4 X 47 ohms = 188 ohms) for empty. You will need to buy five 47 ohms resistors, one at 2W and the rest at 1/4 W each.

Let me know if you need other suggestions to get suitable resistor combinations, there are dozens of options.

Regards

[390xlt]

That is great information. I'm pretty sure I've got a few USB cables sitting around that I can cut up. Seems like a much better option than the car battery I've been using
Thanks!

[zgerbic]

If you are going the USB cable route here are a couple of pieces of info:

1. Once you have cut a cable and found the four wires and plugged it into a USB charger, two will not be connected to anything because they are the data wires. One will be ground and the other hot/+5V. Should be easy to find the right two to use.

2. The gauges draw as much as 1/4A (250ma) to swing the needle over to the full/hot position on the right. Use an older USB charger that can provide up to an amp to be sure you have plenty of power to power the gauge.

Regards