Function testing factory Gauges.

[HotRodPC]

To accuratly test the gauge you would need a potentiometer that can read from 1600 ohms (100*) down to around 90 ohms (250*). But you can still test the sensor circuit with voltage drop tests all the way to the gauge.

Fuel gauge sending unit is 0-90 ohms
0 ohms and the gauge should read Empty
22.5 ohms and the gauge should read 1/4 tank
45 ohms and the gauge should read 1/2 tank
67.5 ohms and the gauge thould read 3/4 tank
90 ohms and the gauge should read Full

Temperature gauge is

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BTW, are we sure that Temp SENDERS for guages are the same resistance for Temp SENSORS???

IIRC, Temp SWITCHES, the ones used for Idiot light, called a SWITCH, because it only has 2 variables. Either ON or OFF, aka CLOSED or OPEN. When the Switch reaches the predetermined point, Usually 253 degrees for GM Vehicles in the 1960-1980's that I'm aware of anyway, the switch goes ON or CLOSED and makes the connection to ground turning on the light. But I'm wanting to say for some reason, the resistance is HIGH for On or Closed meaning HOT, where as the SENDER appears to be HIGH for Cold and gets lower the Hotter the temp gets. Do I have that right? I think that's why I got this **** backwards.

BTW, you can aslo get a switch in the 1/2 pipe thread for GM heads that will turn a light ON or CLOSE a circuit at 210 degrees, which is no biggie and what I use for a Caution light being that 210 isn't overheated. My 454 hits 210 in the summer all the time.

 

[oneluckypops]

Fugger !!! I just downloaded that and was coming to edit your post and put it up.

That's good info there.

BTW, are we sure that Temp SENDERS for guages are the same resistance for Temp SENSORS???

IIRC, Temp SWITCHES, the ones used for Idiot light, called a SWITCH, because it only has 2 variables. Either ON or OFF, aka CLOSED or OPEN. When the Switch reaches the predetermined point, Usually 253 degrees for GM Vehicles in the 1960-1980's that I'm aware of anyway, the switch goes ON or CLOSED and makes the connection to ground turning on the light. But I'm wanting to say for some reason, the resistance is HIGH for On or Closed meaning HOT, where as the SENDER appears to be HIGH for Cold and gets lower the Hotter the temp gets. Do I have that right? I think that's why I got this **** backwards.



BTW, you can aslo get a switch in the 1/2 pipe thread for GM heads that will turn a light ON or CLOSE a circuit at 210 degrees, which is no biggie and what I use for a Caution light being that 210 isn't overheated. My 454 hits 210 in the summer all the time.

Well the warning light is not controlled from high or low resistance. It is just a Normally Open switch that just happens to be temperature controlled. To know what the ohms of the Switch is you need to think about "ohms law" which is.
V = I x R (Voltage = Current multiplied by Resistance)
R = V / I (Resistance = Voltage divided by Current)
I = V / R (Current = Voltage Divided by Resistance)
You have to know 2 of the parts to the equasion before you can find the 3rd part of the equasion.

In order to find out what the Ohms of the Switch is when CLOSED, you would need to know what the voltage is at the warning light, as well as the current.

For example: If your circuit is drawing 3 amps of current, and your battery is fully charged (12.6V) your resistance in ohms would be 12.6(v)/3(I)=4.2(R) ohms BUT if your switch is OPENED you are not drawing any current so so ohms of the switch would then be 0.
Make sence?

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[HotRodPC]

GEEEEEZUS !!! I'm starting feel quite inadequate. First the heater box was kicking my ass. Now this muthafuggin gauge is. I did find a section of wire that was cracked and taped. Even cutting it shorter It was still able to reach the sender and all is well with a new end on it. I figured for sure that was it. NOPE. Rather than pull the whole cluster out I was able to pull the gauge and reaplaced with another, (untested but assumed it was a good one) and helllllllllllll NO still don't work and it acts identical the original gauge. Obviously the issue is probably going to be in the printed circuit I think. Again, I ground the gauge wire and it goes infinite hot on the gauge. So it's obvious, the continuity is there from the sender plug all the way to the gauge. Now WTF???

 

[oneluckypops]

GEEEEEZUS !!! I'm starting feel quite inadequate. First the heater box was kicking my ass. Now this muthafuggin gauge is. I did find a section of wire that was cracked and taped. Even cutting it shorter It was still able to reach the sender and all is well with a new end on it. I figured for sure that was it. NOPE. Rather than pull the whole cluster out I was able to pull the gauge and reaplaced with another, (untested but assumed it was a good one) and helllllllllllll NO still don't work and it acts identical the original gauge. Obviously the issue is probably going to be in the printed circuit I think. Again, I ground the gauge wire and it goes infinite hot on the gauge. So it's obvious, the continuity is there from the sender plug all the way to the gauge. Now WTF???

You are correct grounding the sensor wire does tell if you hasve continuity on the circuit, BUT it does not tell if there is exsive restinace.

Connect the terminal to ground, just like you did to spike the gauge. Then go to the cluster pigtail. Find the sensor wire, then connect the negative lead of the multimeter to the terminal. Connect the positive lead to the POS POST of the battery. Observe voltage, then take negative lead of the tester and connect it to the NEG POST of the Battery. Compare this voltage reading versus the previouse reading. If the reading is more then .03 volts difference you have to much restitance for the sensor wire.

You still have my number dont you? Have questions call me and I will try to walk you thru some more testing.... Dont have time to type it all out right now.

 

[HotRodPC]

You are correct grounding the sensor wire does tell if you hasve continuity on the circuit, BUT it does not tell if there is exsive restinace.

Connect the terminal to ground, just like you did to spike the gauge. Then go to the cluster pigtail. Find the sensor wire, then connect the negative lead of the multimeter to the terminal. Connect the positive lead to the POS POST of the battery. Observe voltage, then take negative lead of the tester and connect it to the NEG POST of the Battery. Compare this voltage reading versus the previouse reading. If the reading is more then .03 volts difference you have to much restitance for the sensor wire.

You still have my number dont you? Have questions call me and I will try to walk you thru some more testing.... Dont have time to type it all out right now.

I'll do that test when I feel like fuggin with it again. I was hoping shortening the wire by a foot to cut out a bad section, that too would also decrease resistance. Now I have to wonder if it did and will make the gauge inaccurate when I do get it working.

Yeah, I stil have it. BTW, I noticed a missed call from you I think it was last week or the week before.My phone was misplaced and had so many missed calls it was down at the bottom.

For now I probably going to hook up my Cold/Hot Idiot lights, although I hate that. Once you're 253 degrees, there's not much you can do but shut it down at that point, but at least it's something. I'd much rather be able to watch it and KNOW where it's at. I've spent to much time on this fuggin heater box and gauge now.

 

[HotRodPC]

For some reason, just has a freakin brain fart about another possible on this Temp gauge not working. When I did that volt drop test Pops spoke of, the difference between actually battery voltage and voltage drop grounding to the block. I was putting the lead on the cast iron passenger side head. Seemed hard to get continuity to get a reading. I moved the probe around a bit gave up and went to the alternator bracket where I got a reading instantly. Now that I think about it, where does the negative battery cable go??? Alternator bracket !!! Duh !!! I'm starting to wonder if my block isn't fuggin grounded good enough. I might just look into doing the Big 3, and my damn Temp gauge just might start working.

I've also been looking for steps to test a Temp Gauge and I guess there isn't a test to determine if the gauge is good or bad. Meaning, I want to directly test the gauge itself outside of the vehicle, like you can test a coil or ign module. Seems all the tests I find, are process of elimination tests. I wanted to ohms test a gauge at PAP before I bought it. Well, 2 went home with me anyway, untested but being they FELL into the tool box...

 

[HotRodPC]

This info is for a fuggin Jip. But this is the kind of info I'd like to find for Squares. Notice the Internal Gauge Resistance Charts. This is the info we need to be able to test our own gauges if they are defective or not. And also test senders too.

http://home.sprynet.com/~dale02/specs.htm

 

[oneluckypops]

ou know Hotrod there is another possability that is not even electrical that may be causing your issue.

The ECT Sensor is designed to be submerged in coolant when its threaded into the head. If there is an air pocket around the sensor It will NOT register. Doubt that is whats wrong with it but a possability that needs to be checked out.

You could also move the sensor from the head to the waterpump.

If somebody wants to send me a few different clusters, I would be willing to exsperment with building a test harness. or maybe when I get moved to Texas and get settled I might be able to find a PAP yard and get a few from different years. I am just not sure what years used which printed circuit board.

Edit: Just did some looking on LMC and come up with this info.
73-75 used the same printed board
76 was a year of its own, BUT there were 2 different options for indicator lights.
77 year of its own
78-80 Interchange
81-87 Interchange

If that is all true then If I had 1 of each of them I could work on getting the test harness built for each of the years. Ofcourse with pictures and a how to build them to that others could build them so they can test theres. Anybody up for it?

 

[HotRodPC]

Thinking more along the lines of Pops making Test Clusters.... I was going to do that with this 81 Cluster I have. I then realized, if we knew the pin out on the gauges, we can test each gauge manually with alligator clips under the hood. Positive to +, Negative to -, and the the sender wire to a good known sending unit. All my gauges work in the 84C20, so I know the senders are good. If I knew the pinout of what leads on the gauge to what, then I could test each one individually. Can't find my Electrical Shematic book for wire colors and BS to figure it out after looking at a printed circuit. So I could figure it out, thought maybe someone might KNOW the info already. ???

 

[RetroC10Sport]

 

[HotRodPC]

You're fuggin Awesome brah !!! I knew I could figure it out, but someone, and figured it would be you first, Pops second would have hooked me up pretty damn fast. Thanks,

 

[HotRodPC]

I haven't checked it out yet, but next ave, is to figure out what this black wire above the fuel gauge goes too. It wasn't hooked to anything. Kinda wonder if maybe it's not a cluster ground.

My cluster and behind my dash is very very filthy. I'm hoping to clean all that up today, make sure all bulbs ae good, found 2 bad already. Now I know why the 4x4 light didn't work. Make sure I know where every wire goes and it's hooked up, and looking over the printed circuit looking for any breaks. Everything worked in this cluster except 4x4 light and Temp gauge that I recall. So unless those other gauges get a ground from another source, I'd say that black wire probably isn't going to fix my temp gauge, but I at least want it hooked up where it goes.

 

[RetroC10Sport]

This one? If you look closely, it's not a wire at all. It's a fiberoptic cable that goes to the ashtray to give light when the dash lights are on. I'm thinking your temp gauge is bad or your sender is bad or not grounded right because the gauge uses the same ground as the dash lights and other gauges.

 

[HotRodPC]

This one? If you look closely, it's not a wire at all. It's a fiberoptic cable that goes to the ashtray to give light when the dash lights are on.

Awesome Again. I figured it had to do something like cuz it looked like a light not a plug.

I'll post pics, tested 3 guages. The one that came out of the truck OE, so it's going back in. Dead nuts match to the 84 C20. The one I got out of the 89 Burb at PAP, dead nuts read the same as the C20 too. The one that just says C and H out of a late 70's read about 1/2 way up from where the other 2 were at. Could be a different scale, but nonetheless, the orange was chipped off the needle in several places, so I'm **** canning it anyway. I've got pics I"ll post later. Taking full advantage of this awesome friggin weahter. In a Tshirt out there running around with a nice litle breeze and sweat on my forehead. AWESOME weather, and I only got about an hour and a half left of it.

 

[HotRodPC]

Sucks, I have a new gear selector mechanism for the K1500. I just noticed the ever so common broke part on the cluster housing, IS broke. Maybe I can transfer all my guts into the 81 clusterr housing. I'll be looking at that option. If I knew for positive this truck was going A833, I'd blow it off. But that might be going in another project and thinking of putting a well built 700r4 in the K1500 someday.

That does gimme ideas though. Next time you're at Budget Wrech Retro, get me a few of those Fibre Optic wires if you don't have a use for them.