Very soon I will be putting things together on my project car. been wondering about a safe way to test all the electrical accessories while I assemble the dash. Is there anything to be aware of or can I simply use a car battery through a bench fuse block?

As long as you supply power at the same place that it would be if hooked into the car, you will be OK. I test them with a 12v power supply. Do you know how to test the fuel & temp gauges?

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Chuck Rivers, Webmaster

Nope

You can test the with or without the sensors (if you are careful).

After you power it up, ground the lead that goes to the sensor. The gauge will slowly move to the right. Don't leave it connected for more that a few seconds.

If you have a temp sensor, you can hook it up to the sensor side of either gauge. You usually won't get much of a reading. I use a temp sensor and then heat it with a lighter to see if it moves.

You also need to check the output of the voltage regulator on the back of the instrument panel. It will "pulse" from about 0 to 4-5 volts if it is working correctly. If you get a lower reading, your gauges will read low.

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Chuck Rivers, Webmaster

Not sure how involved you want to get but the temp gauge and the fuel gauge should be able to be tested with a potentiometer that has roughly the same resistance as the sending unit. IIRC something like 10-70 ohms not sure for the temp gauge

I do a lot of testing for the Tidewater Mopar Club giveaway cars. For bench testing, I took my simple old 6/12V 10A battery charger and modified it for additional use.

This charger is basically just a metal box with lots of empty space inside and nothing sophisticated or tricky; it does have a 10A ammeter.

I added a ~6A fullwave rectifier & a large electrolytic capacitor to make an unregulated DC supply and connected that to a female banana plug to the outside. Another banana plug provides ground. Then I used the unregulated DC to feed a series 12V regulator chip with its ground biased with 2 Si diodes to provide regulated ~13.4VDC @ ~1A and put that to another banana plug.

Next I added a switch to disconnect the stock battery cables and a dual-color LED with one side connected to the (+)cable and the other to the stock (+)rectifier. With the switch off, green means the AC is on, and red that the battery is connected, so orange means I've ready to charge. Also, being able to disable the battery cables means I don't have to worry about them shorting out.

It was was a very cheap mod, the charger still works as well as ever, and there's still lots of space left for more stuff inside.

Nice mod on the charger, but probably too much for most of our users.

The readings that I got on temp sensors was about 270 ohms cold. I seem to recall that the fuel sender was 0-300, but I don't have one to test with at the moment.

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Chuck Rivers, Webmaster

Thanks Chuck; the mods really were quite easy and I had all the stuff just sitting around...

For the 60s-70s sensors, usually ~80ohms was cold/low/empty and ~10ohms was hot/high/full. These numbers are not precise, just approximate; the factory didn't really intend them to be all that accurate. I put a 10ohm and a 80ohm power resistor into a box and now have a little handy tester.

Note that many aftermarket replacement oil pressure senders are really not direct replacements and are very nonlinear and go open (infinite ohms) at 0psi; I assume that did that so they could use them with idiot lights too. I spent considerable time at NAPA looking for one that behaved just like stock w/o success; but the one I ended up with (that goes open at 0psi) seems to work fine anyway.

Interesting readings on the temp sensors. I just tested 7 sensors, four of the large type and three of the small ones. The readings I got were:

Large: 245, 284, 290, 304

Small: 198, 637, 20k !!!

The last 3 of the larger ones were about what I expected, with the first one reading low.

The small ones were all over the map! I'm sure the 20k unit is shot. I'm wondering if the 637 ohm unit is from another car but looks the same. The only reading that was in the range I have seen before was the 198, and that seems low.

I didn't see anything in the range that you got.

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Chuck Rivers, Webmaster

Thermistors are quite nonlinear. If the temp sender reads anything reasonable over the range 160-240F, that's all you need; the guage isn't going to show anything at 70F anyway. LO ~ 120F ~80 ohms or so, I'd imagine, and HI ~ 240F ~ 10 ohms. Boiling water makes a pretty good temperature reference if you want to calibrate things, and I've found an inexpensive candy thermometer worked well for testing thermostats.

BTW, I'm seeing my cheap Chinese-made DMMs read off +/- 5% on voltage; I imagine resistance is no better.

How do the pros do it? I've wondered about testing a guage cluster befor installation to avoid the whole in and out thing. You would think that with a proper power source and grounding that it would be easy to check things befor installing them.

I would also like to do the 1 time dash in/out senerio. It would be nice if I could set up and do all 4 dashes at one time even though they range from 66 to 85. Would this be possible?
Thanks
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
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It should not be that hard. Power could be supplied with a car, motorcycle or lantern battery, or with a power supply. I don't usually hook up sensors when I do it. I short the temp & fuel gauge sensor lines to ground long enough to see if the gauge rises. If they do, I call it good. If that test works, the unit has always worked in the car.

You could hook up sensors, but then you would probably have to boil some water and insert the temp sensor to test that gauge, and have a fuel tank sensor and move it up and down to test the fuel gauge. I have never had to go to that much trouble to test the panel.

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Chuck Rivers, Webmaster