c-3826 tester for gauges and sensors

[kenmdale]

After trying to find a C-3826 electrical tester, I decided to make my own. What I used was a 0-100 ohm variable pot resistor ( about $12 Canadian ) and a solar powered deck light I had kicking around ( I didn't feel like making an extra trip out for a box).After installing the pot resistor into the case ,I used a good ohm meter to set calibration index marks around the face of the case. The paint I used was the same paint I used for the needle pointers on the gauges ( bought from a local dollar store ). I also ran the wiring long enough to sit on the dash while viewing the car gauges
Full =10 ohms
Med =23 ohms
Empty=74 ohms

I apologize if someone has covered this already


Ken

 

[commando1]

This is a Guage calibrater, yes?

 

[kenmdale]

That's what I was using it for

Ken

 

[BJS racing]

I've used an old headlight switch for that as well.

 

[commando1]

I've used an old headlight switch for that as well.

Brilliant. Thank you. I got one sitting around. I'll move it from inventory to test equptment. Lol.

Now I need a 0-100 variable resister for the fuel Guage.

 

[BJS racing]

Stan I have used the headlight switch to test fuel, temp and oil pressure gauges. If you hook the B2 terminal on the headlight switch to ground and the I terminal to the sending unit terminal of the gauge or the wire to the sending unit, pull the switch to the park light position and rotate the knob the gauge should go up and down accordingly.

 

[commando1]

Stan I have used the headlight switch to test fuel, temp and oil pressure gauges. If you hook the B2 terminal on the headlight switch to ground and the I terminal to the sending unit terminal of the gauge or the wire to the sending unit, pull the switch to the park light position and rotate the knob the gauge should go up and down accordingly.

A zillion semesters of Electronics and I still can't get it right.
But that was 45 years ago. Around Tesla's time. .. LOL

 

[kenmdale]

I've used mine for temp and fuel, i still need to test my oil pressure light. I don't feel like working in an unheated garage when it's 10 degrees F outside

 

[cantflip]

Stan I have used the headlight switch to test fuel, temp and oil pressure gauges. If you hook the B2 terminal on the headlight switch to ground and the I terminal to the sending unit terminal of the gauge or the wire to the sending unit, pull the switch to the park light position and rotate the knob the gauge should go up and down accordingly.

That is a brilliant substitution... Wish I thought of that, but will definately "steal" it should the need arise. I usually assume gauges are inaccurate and just ground the signal to get a full sweep... but in conjunction with an ohmmeter, you could calibrate with this.

After trying to find a C-3826 electrical tester, I decided to make my own.
Full =10 ohms
Med =23 ohms
Empty=74 ohms

Ken

Ken, I doubt the factory tool would have the calibrated accuracy of your homemade tool. Very nice, cheap and simple... just as I like it.

These resistance tools were dealer tools so I did not need to purchase one. They were expensive for what they are, so I just kept a small collection of resistors in my electronics drawer and would put one into the circuit to test when the need arose. You can get a nice variety of resistors for a buck or two vs. a couple hundred for a "decade box" or "gauge tester". I learned pretty early that all you usually need is a good meter and understanding. Not before I bought that dumb OTC ignition module tester though. It has a place of honor in the box as the dumbest thing I ever bought.

 

[65sporty]

A couple of great idea's for testing, love it. I never thought of using the headlamp switch rheostat for that

 

[HWYCRZR]

Thanks all for the thread. Was out googling C-3826 tester for gauges and it took me right back here. So I ordered the parts two variable resistors and knobs delivered for $18. Not sure what I will do with the second set yet but sometimes you can never have enough spares. I happened to have an Bakelite electrical box that was looking for something to do. I calibrated to a couple of posts above and seems to work great. One thing I noticed is that if you used a power supply the gauges fluxuate quite a bit. A battery is much more stable.

 

[Big_John]

I bought a decade box like this for $25 on eBay. Just dial in the resistance.

 

[commando1]

25 bucks? Seriously???

 

[HWYCRZR]

That’s some good shopping.
I did notice mine could only do one gauge at a time. I could find a bigger box and use my spare to have a dual system. But then again my gauges are tested and would probably have limited need to test two at once. But if I stumble across a box or object that would accommodate two potentiometers and am board it might happen.

 

[Big_John]

25 bucks? Seriously???

View attachment 163683

That's probably a pretty decent price for that one, but you don't need that accuracy to check your gas gauge.

Here's one like mine that sold for $15 plus shipping.

Vintage EICO Model 1171 Resistance Decade Box | eBay

The Eico decade boxes were often sold as "solder it yourself" kits, similar to Heathkit, but possibly better quality. They aren't anywhere near as accurate as even a cheap Yokogawa or similar, but if they haven't been abused, they work quite well for this use. You can check them with a good DMM. In fact, the proper way to use it is with a DMM in parallel with the decade box.

Here's another. Probably will hammer at less than $20.

Eico Resistance Decade Box Model 1171 | eBay

Something like this will work too. You are really only using the 1 and 10 ohm dials. I like to see that they at least checked it with a DMM before listing it, so I might shy away from it. It's also not as old as you might think.

Vintage Welch SCIENTIFIC 3-DIAL RESISTANCE DECADE Box | eBay

 

[Fury440]

Stan, that fancy box is way more precise that you'd ever need. Check the specs, very nice, very pricey.

The $25 boxes are much more useful, the first decade uses 1 ohm steps, the second 10 ohm steps, the third 100 ohm steps, etc. Generally all resistors will be 1% but some are %5 or more. If you need a reasonably accurate setting, use an ohmmeter to adjust for the value wanted.

Back in the day, I made a decade box using adjustable linear wire wound potentiometers with 10:1 vernier dials. For example the first decade used a 10 ohm so the 10:1 vernier could be set in 0.1 ohm steps. The second, a 100 ohm pot with 1 ohm steps, etc. Again, an accurate ohmmeter was required to get the exact value.

For those thinking of getting a decade box, be very aware of the wattage of resistors used and how much current each decade will handle. Exceed the current and you cook resistors rendering the box useless. Because of this, beware of "experienced" units on ebay or Craig's list. On the box I made, I put fuses on each decade.

 

[Big_John]

For those thinking of getting a decade box, be very aware of the wattage of resistors used and how much current each decade will handle. Exceed the current and you cook resistors rendering the box useless. Because of this, beware of "experienced" units on ebay or Craig's list.

I should have mentioned this, but that's exactly why I don't like buying one that hasn't been tested for operation.

Used electronic stuff is always a bit of a gamble, especially when the seller specializes in something like Looney Tunes glasses and just happened to find some old test equipment in someone's garage next to the box of Snuffy Smith Pez dispensers.