Need help finding new temperature gauge

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FrozenCaveman

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I need to replace the temperature gauge in my 71 Scamp. I've replaced the voltage limiter with a solid state equivalent, and both my gas gauge and temperature gauge are not functioning. I think the sending unit on the gas tank is bad, but I know the temperature sending unit is good.

For now, I'd like to replace the temperature gauge and looking at what Classic Industries has, I see a couple of possibilities:

http://www.classicindustries.com/mopar/a-body-scamp/parts/?q=MA1545

http://www.classicindustries.com/mopar/a-body-scamp/parts/?q=MA1547

MA1545 looks to have the same print pattern as my original gauge.

MA1547 is listed as the correct gauge for my year, and has a completely different footprint than MA1545.

Without taking apart my dash again (it's my driver), can anyone help identify which gauge will fit my 71? I'd like to keep the appearance original, which I why I'm looking at MA1545. A known-good working used gauge would be fine if someone has a line on one.

Thanks,

John
 
Before you do that, make some tests. I keep trying to get guys to think of the instruments as AN END TO END SYSTEM.

There are many many things that can go wrong besides the gauges themselves. You MUST pull the panel out and simply go through each possible "point."

1--For temp, fuel (and oil if equipped) bad senders

2--For temp, fuel (and oil if equipped) bad wire connections at the senders

3--For temp (and oil if equipped) bad connections in the bulkhead connector

Bad connections at the harness connector at the cluster

Broken or loose connector pins on the instrument panel. You can repair these. On my 67, it was so bad I abandoned the original connector, soldered pigtails to the board, and bought "Molex" style connectors from Radio Shack

Bad contact fingers at the instrument regulator. On my 67 I had to solder jumpers from the contact fingers to the PC board traces

Bad or out of cal instrument limiter. I bought an aftermarket RTE, but I heard something the other day someone was having troubles contacting them. Who knows.

Bad nut connections at the gauge studs. Replace the "fake" nuts with real ones

Bad or out of cal gauges. Read onwards

Out of the gauges, through the PC traces, back out the connector pins, through the harness, bulkhead connector (except fuel) to the senders which can also be out of calibration

You can check gauge calibration several ways. One is to use a 1.5V dry cell, but I've forgotten. I prefer to check using the IVR, gauge, and a "dummy" sender of a resistor, with 12V battery just as it would be operating, installed in the cluster.

You can go to Radio Shack and buy resistors to test. All the gauges are the same movement.

For example, 1/2 scale is 23--35 ohms, so if you buy a pack of four 100 ohm, 1/2 watt resistors and wire all 4 in parallel, this makes one 25 ohm resistor. With 12--14V power to the IVR, and the 25 ohm resistor from the sender terminal of the gauge to ground, "about a minute" should result in a 1/2 scale reading on the gauge

Sender resistances are

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)
 
OK, sure, I'll give it a go. I just got back from RadioShack with a 5-pack of 100 ohm 1/2 watt resistors.

I've never worked with these components, so you'll have to speak more slowly. What does it mean to wire them in parallel? It sounds like I should not run them end-to-end (serially?), but rather solder all 4 so that 4 ends of the resistors go to 1 wire and the other 4 ends to a 2nd wire?

Can I do this with everything out of the vehicle? Run a positive terminal battery wire to one end of the IVR, a wire from the other spade of the IVR (I think there's 2, having just recently replaced mine) to the instrument, and then run the ground terminal from the instrument through the "resistor I built" to the negative terminal on the battery? Would that work?

A garage told us that the fuel sending unit was bad, so that's why I was just making the assumption that I don't yet need to test the fuel guage. Specifically, I'm more interested in testing the temperature gauge. With the cluster out, I might as well check both.

Is there an easy way to test my IVR? Run the positive battery wire through it and back to the negative terminal on the battery? It should have 12 volts input and 5 output, right? I haven't worked with electronics much, so I apologize for the basic questions that make you cringe.


Thanks!
 
Yep. Parallel means make them sort of like a ladder. Just lay all 4 side by side, and twist all four wires at one end, then twist all 4 wires at the other, and solder

Testing the IVR is a little tough. You would really have to check the gauges first. "Somewhere" I've got what it takes (for voltage) to directly operate a gauge. I believe it's 2 dry cells should give you full scale on a gauge movement with nothing else tied to it, but not sure

You can also check them "against each other" If they are in the cluster, pull the IVR out, and hook a battery to the two sender connections on the two gauges (temp and fuel) Polarity does not matter. The two gauges should both come up to the same reading.

The problem with trying to test IVR is that the old ones "pulse" like a flasher. The reason you don't see this on the gauges is that the gauges react slowly. The replacement solid state ones may not regulator properly without some load, so trying to test them gets tricky as well

Be careful what you hook up. Running full 12V to the gauges will likely burn them up

Edit. Here we go. These are to show that two gauges agree, meaning that either they are both wrong---and off aby the same amount, or else the fact that they agree tends to show they are still accurate

Check out these two threads

http://www.forabodiesonly.com/mopar/showthread.php?t=207604&highlight=gauges

http://www.forabodiesonly.com/mopar/showthread.php?t=205270&highlight=gauges


The top photo is with both gauges wired in parallel. They are being supplied 3V from a power supply, and you can see they both read close to full scale

The bottom photo is in series, and you can see both show between empty/ cold and the first mark on the scale
 

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I finally had time today to get under the car, and I'm not having much luck with the wiring. The one thing I've verified is that the fuel sending unit is good (putting out about 80-ish ohms on a somewhat full tank). Beyond that, I'm not getting any continuity between the sending unit wire and the harness connector behind the driver kick panel. I also don't get any jump in the gas gauge if I ground the gauge-side harness connection. I can't see any reason for the lack of continuity between the sending unit wire and the front of the rear harness. Not sure of how better to test the wires - I've been had my ohmmeter connected to the sending unit wire and a wire from the harness connector long enough that i could connect both it and the sending unit wire together - nothing. I guess I could be having 2 problems, a bad wire and a bad gauge. At this point, I can't tell anything else.

How do I test the dash ground? It lights up with the headlights on, although the left turn signal indicator is dimly lit, and the turn signal indicators otherwise function normally. However, I can't seem to get either of the brake or oil idiot lights to come on. The moparfins article doesn't go into testing the dash ground, just says I might have a problem with it based on what I'm seeing.

Ideas?
 
Well, 80'''ish ohms is not correct. The less resistance (lower the ohmic number) the higher the gauge reads. It should read 73--75 at empty, 23--25 for 1/2 and about 13 for full tank

The sending unit wire only goes one place.............connector at the sender.............up front in the rear harness to the kick panel..........from the kick panel to the dash connector

So if you have no continuity, check each point, IE from the sender to the kick panel connector. Make sure you have the correct wire. It is VERY possible that the sender connector itself is bad, corroded internally

You have the cluster out? Can you post a big clear photo of the back of the cluster?
 
I'm sorry, the reading I got from the sending unit was in the mid-teens. I was reading the document from moparfins and just remembered it was 10 off a full reading, then had a brain fart and typed the wrong value in the reply. I'm confident the sending unit is good.

I'll check the connector again tomorrow. I wish I could poke a test light into the blue sending unit wire and check it that way, but it's just a ground. :/

I will take the cluster out tomorrow and get a picture. Thanks!

-John
 
You CAN use a test lamp, you just need a battery. I quite often "jerry rig" stuff.

You have some RadShack clip leads? Just take a length of wire long enough to reach the sender, Hook one end of your light to that wire, then hook the other end of the light, and a probe going to the kick panel connector to a battery.

Just use your head..........."How can I hook this up?"
 
Woah ! back up a bit a take a wider view. Only 3 parts of the inst panel should get power at switch on... Inst' voltage regulator, park brake indicator lamp, and oil warning lamp.
So if none of those 3 are working you have to guess maybe the 12 volts from ignition switch isn't happening at switch on.
Many times the only thing needed is logic and common sense. A lot of high tech skill and knowledge isn't required.
 
Here's a pic of the back of the cluster. I hope the resolution is OK.

A couple observations: I replaced the voltage limiter a few weeks ago with the cluster still installed, and I'm not 100% sure that the capacitor (is that what it is?) was connected when I removed the cluster. I _think_ it was, but just not sure. The area that wire runs over the circuitry looks a bit worn. The new VL is a solid state model from Napa.

The lamp for the brake indicator was missing - I think this is because the e-brake switch was severed previously and someone had the bright idea to just remove the lamp? I repaired the e-brake wire a while ago. I'll have to hit up Napa and get a new socket and bulb unless I can manage to find one in my assorted parts from other cars.

There is corrosion on 3 of the spades for the headlamp switch. The cowl was plugged up with leaves when I got the car and when it rained heavily, water collected in both air boxes.

From what I can see, the rest of the cluster looks pretty good.
 

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Some things to do.

1.....Look up the destructions for your multimeter, and see if there's a special setting for low resistance measurements. Or post the brand and model here

2......Take your meter and place one probe onto each of the harness connector pins, with the other probe stabbed into the copper trace on the board which hooks to it. Wiggle the pins and see if the resistance changes or that there's any physical movement. Best plan is to clean them and solder them from the pin to the copper.

3.....See the screw immediately to the left of the VR? That screw, and any other screw which screws into the cluster and which goes through copper on the board is a ground, but there's nothing to ground the cluster "for certain" to the car. Hook a pigtail wire to that screw long enough that you can bolt it to the column support before you finally insert the cluster.

4.....Pull the VR out. You'll see those brass contacts which act as the VR "socket." Those MAY NOT be making good contact with the board traces!!!! Solder them across. Check with your ohmeter

5....Notice the fake nuts on the studs of the gauges. These may not be making good contact. Loosen/ tighten them several times to scrub the connection clean. A better plan is to replace with real nuts. Do not overtighten.

If you look at the PC board, you can SEE where every circuit goes

For example, look at the trace coming off the lower right of the VR which goes to the right hand stud on one gauge, and the left hand stud of the other. This is the regulated output of the VR. The remaining studs of the two gauges go by PC trace up to the respective pins of the harness connectors and off to the temp and fuel senders

My poor edit shows the screw which is ground, and the circled area is power output of the VR going to the gauges
 

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My ohmmeter is an Equus 4340. I also have an old, non-digital model that is a C1000 mini multitester from Japan.
 
P.S. My pregnant wife is getting annoyed with me tinkering on the vehicle, I may need to "chill" for a bit.
 
Harness connector pins all tested fine - they don't budge at all. The gauge nuts were all a little loose, and I alternately loosened and tightened them some. My soldering skills are terrible, so for now I'm going to leave the VR connectors as they are. They seem pretty solid. The only one a tiny bit loose is the center one, and with the condensor and the VR pushed in, I think the contact is good. For kicks, I tested continuity on the 2 gauges and got a pretty good reading of .015 on the lowest setting for resistance. I don't know if that tells me anything other than the gauges aren't completely broken?

How is the cluster "supposed" to ground? I see 3 separate screws that would go to ground, but by what theory are they supposed to contact the chassis? Through the screws that attach the cluster to the dash? If I had bad ground, I think I'd have problems with my other lights, no?

Thanks!
 
That's the whole problem.............the cluster depends on the dash --- to cluster mounting bolts, which is not all that dependable. That's why I suggest a separate pigtail

You can easily test the cluster / gauges out of the dash now that you have some test resistors

Clip your 1/2 scale (23--25 ohm) resistor to the sender stud on one of the gauges, and clip the other end of that resistor to ground.

Hook the cluster ground to battery neg.

Hook the proper pin of the harness connector to the battery hot, and watch the gauge.
 
I don't want to fry my gauges if they're still good - can I ground my set of resistors to the battery negative terminal as well? That little contraption is working quite well - I was proud of myself, even as bad as the soldering was - I got exactly 25 ohms.

I think the toughest thing will be to get 12v just to that one pin without hitting any of the other pins. I'll probably use a female spade connector and jam it over the pin so I don't risk a wayward alligator clip. :)
 
Use your ohmeter. The tab where the radio suppression cap hooks up should be the same electrical point as the pin for the harness connector to 12V. That might be an easier/ safer point to attach.
 
So here's how I connected things: I plugged the harness pin for 12v into my battery booster, plugged the ground for the VR into the negative terminal, plugged the gauge terminal (the one going to the harness, not the 5V) into the negative terminal as well.

The fuel gauge works - but goes to full. Not sure why that is.

The temperature gauge doesn't budge, so I imagine that it's kaput.

Any ideas why the fuel gauge would go to full? It's like there's no resistance. My resistors measured to 25 ohms, but am I somehow neutralizing it by connecting the 2 ground wires together at the negative terminal of the battery?


-John
 
I don't know what you did. You have to have each gauge separately hooked through a test resistor. So if you did not have a test resistor------to simulate the sender---hooked to the temp gauge, it won't move.

Do NOT use a booster / charger. Use a 12 V battery or a regulated 12-14V power supply.
 
I tried one gauge at a time since I was limited on my selection of wires/connectors. The 25 ohm resistor didn't budge the temperature gauge, but separately the fuel gauge went to full. I'll give it another try and use the multimeter to confirm the connections, but having tried twice already, I doubt it will change.

I'm using a portable battery pack jumper from Costco, not a charger. It pushes 12V (which I confirmed with the multimeter). I have an old battery that I tried at first, but it had under 11V and wasn't enough.
 
OK, so your power device is one of those things with a battery inside? That should be fine

Still not clear to me what's wrong..............

Be certain the battery neg is connected to the cluster ground

Be certain the battery pos is connected to the proper pin going to the VR

Start with no resistor anywhere

Neither gauge should move.

Now connect one end of the resistor to the cluster ground.

First connect the remaining end of the resistor to one gauge, and then the other.

Both gauges should do exactly the same thing................

No resistor...........remain on cold/ empty

Resistor in place.......eventually 1/2 scale exactly.

You might want to measure your resistor to be certain it's 25 ohms. They can be mis--packaged!!!

Below is how to wire it in case you messed up

12V is where you should connect battery, and should be the same point as where the condenser / capacitor wire is connected

GND is battery neg, and also where you hook one end of the resistor

R is where you hook the remaining end of the resistor, one at a time,
 

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LOL, you have good reason to second guess me. I was using a straight wire instead of my resistor setup. The wife was dogging me and I lost my focus, I guess. :p

With the proper wire, I got the temperature gauge to read near the bottom of the normal range, and the fuel gauge read steady about 1/4 tank after a couple minutes. Testing just my resistor wire on the 200 ohm setting, I got 25-26. With it hooked up to my fuel gauge, I was having trouble getting a solid reading, but it was anywhere from 35-52, so maybe a loose connection, and that range explains the low reading on the gauge. I was just pressing the bare wire to the gauge stud with a plastic clamp.

The important thing is that both gauges are giving off a reading, so you probably saved me the expense of new gauges. :D Since the cluster seems to be functional, I'll try reseating it.

It's just past midnight here, so I won't be putting the cluster back in until tomorrow night. I also need to make a quick run to get that brake lamp bulb and socket.

Thanks so much for your help, and I'll update again tomorrow night.
 
Great news! I put the cluster back in the dash and both gauges work! Woot!

E-brake lamp works, but the oil pressure lamp does not. I assume it's supposed to light up as I'm starting the car? Can I ground the oil pressure sending wire in order to get the bulb to light up, or no? I tried it and still nothing. The bulb and socket are in good order, but unfortunately I did not test the circuit board before replacing the dash. :(
 
It looks like the oil light has the same 12V power source as the brake lamp, so either the socket isn't making good contact with the circuit board or the ground is bad. What I'm reading tells me that if I ground the oil pressure sending wire, the light should go on.
 
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