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Old 10-28-2005, 08:23 PM   #1
Longhorn Man
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Question Guage testing

I am about to assemble a nice inst panel that I plan on selling. I have quite a few parts laying around, but I have no clue as to what works, and what does not work.
What can I do to test them...remember, I can't just plug it into my truck becouse I have deleted all the stock acc guages, and assosiated wires on my rig so i could do the aftermarket guages.
Anyone have OHMS readings or anything?
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Old 10-28-2005, 09:50 PM   #2
VetteVet
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Re: Guage testing

According to the Haynes wiring diagram all the gauges are fed 12 volts by a pink wire and the other terminal is connected to a variable resister to ground.
The variable resister being the temp sender, oil sender (electrical) and the fuel float sender. It seems to me that if you apply 12 volts to the plus side of the guage and ground the - side you should get full movement of the needle to the left and if you add in resistance you should get a reading of some sort on the gauge. I have a couple of instrument clusters from a 68 and a 70 that I can test this theory on and let you know. I think I remember that the temp sender was 75 ohms. I'll measure one tomorrow now that you have my curiousity aroused.
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Old 10-29-2005, 11:06 AM   #3
clay68c10
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Re: Guage testing

The fuel sender is a 0-90 ohms type. If you can find a resistance substitution box that would make things easier. Just put it in series between the 12v source and the gage and dial up wheatever ohm setting you want.
The full voltage/no voltage trick also works just so you know if the needle will make a full sweep. The only problem with that test is that you have no idea if the midrange of the gauge is accurate or if it has any dead spots.

Here's a link to the resistance box, also called a decade box.
http://mcm.newark.com/NewarkWebComme...KU=72-7270&N=0
I use one like this at work fairly often. They can come in handy if you have to troubleshoot sensors a lot. I work on Benzes, and they have an a$$load of sensors that like to break.
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Old 10-29-2005, 08:17 PM   #4
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Re: Guage testing

Quote:
Originally Posted by Longhorn Man
vet...that'd be sweet. it would give a way to verify the chart above...which looks pretty cool too.
thanks guys
Here's what I got on a 68 gmc and a 70 chevy panel.

ammeter-less than 1 ohm I didn't check it with my digital meter

fuel gauge--32ohms post to post on both
left to ground 65 ohms right to ground 63 ohms

temp guage--42 ohms post to post on both panels
temp resister 55 ohms

I first measured with my analog meter then I used my digital cause I'm anal like that.I like to double check.

fuel gauge was 37ohms and the temp gage measured 48.7ohms and there was about a 10ohm difference in that the 70 panel was higher on both gauges. That could easily be age or conductivityon the terminals.

I see that is pretty close to the chart readings.

I applied 12 volts to the terminals on the temp gauge and it went to less than zero
the fuel gauge went to full plus so I guess they work. I couldn't find a potentiometer that was in the 90 ohm range so I could check the fuel gauge but I figure it will work.
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Last edited by VetteVet; 10-29-2005 at 08:27 PM.
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