66 cluster/gauges questions before reinstalling

[msg]

The cluster that I pulled from my 66 years back has been sitting around, and I thought before I just take it apart and do the sprucing I would ask if there is a way to check each gauge to see it if works properly before I put it all together. The speedometer from memory worked fine, but I dont remember how great each of the others were. I do recall the fuel gauge not behaving so good but that might have been the sending unit or wiring which will both be replaced with new.

So is there a way to test them?

Also, I plan to rig up that ebrake light I saw on this site a while back that replaces the tandem lock light. The over speed light though, I dont even know what thats for if I need to worry about it.

I wish I could afford the vacuum and tach replacement but those will have to wait.

[PGSigns]

For the speedometer I use a small chunk of old speedo cable in a cordless drill. Run it to see if it is smooth and test the odometer. on the gauges the first test is an ohm meter. if they are not open most the time they will work. There are threads on redoing them and getting them looking good.
Jimmy

[ray_mcavoy]

The temperature and fuel gauges can be tested by hooking them up to +12V power and ground (cluster case) and using resistors to simulate the sending units. Connecting the fuel gauge sending unit terminal directly to ground (0Ω) should make it read empty. Connecting it to ground through a 15Ω resistor should make it read half, and through a 30Ω should make it read full. Connecting the temp gauge sending unit terminal to ground through a 500Ω (or higher) resistor should make it read on the cold end of the scale. And something around 80Ω should bring it up to the hot side.

The battery gauge (ammeter) can be tested with a 1.5V battery (such as a AA or AAA). Connect it directly across the two terminals and the needle should swing in one direction. Reverse the polarity and the needle should swing in the other direction.

The oil pressure gauge can be tested by hooking it up to a compressed air source with an adjustable pressure regulator (preferably one with it's own gauge so you can see if the pressure readings match).

[msg]

Thanks Jimmy and Ray, I do have a multimeter and the 12 v source to use. Ill need to study up on how to adjust the multimeter for the readings I will need. Im electrically challenged trying not to get electrically charged.

On the resistors, Ill need to shop for the 4 different ranges you mentioned Ray and wire up some jumpers for testing.

[ray_mcavoy]

You're welcome! When shopping for resistors to use for testing, you won't have to be too concerned about wattage or tolerance ratings for this application. Also be aware that you can combine multiple resistors if needed to obtain the desired resistance.

When resistors are connected in series, the resistance simply adds up: Rtotal = R1 + R2 + R3 + ...

So for example, you could buy two 15Ω resistors, use just one of them to test the fuel gauge at 1/2 tank, and then connect both of them in series (to give 30Ω) for the full tank test. Similarly, you could connect a 15Ω and a 68Ω resistor in series (to give 83Ω) for the temp gauge hot test. And since you don't already have some, I wouldn't even worry about buying any additional resistors to test the temp gauge near the cold end of the scale ... simply leaving the sending unit terminal disconnected (infinite resistance to ground) should make the gauge peg to the cold side.

[msg]

Ray had messaged some more info on what I would need and detailed setup instructions so I am including that in here in case it might benefit someone else in this situation.

Testing shopping list

12v battery,

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

test leads,

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1


and 15 ohm resistors.

https://www.ebay.com/itm/1-2w-Watt-1...72.m2749.l2649

Originally Posted by ray_mcavoy

Yeah, one of those A23 12V batteries should work okay for testing. And those aren't capable of producing anywhere near the amount of current as a car battery so you'd probably be okay to skip the fuse.

To make the test connections, clip one of the test leads to the +12v terminal on the back of the gauge (I usually use a red lead for this). Clip another of the test leads to the sender terminal on the back of the gauge (I usually use a green lead for this). And clip a couple of test leads to a convenient spot on the metal cluster housing (I use black leads for this). Now clip the other end of the green (sender) lead to one side of a resistor, and one of the black (ground) leads to the other side of the resistor. Finally, connect the other black (ground) lead to the negative battery terminal and the red (+12v) lead to the positive battery terminal.

Like this:

[+12v terminal on gauge]-----(red test lead)-----[positive battery terminal]

[sender terminal on gauge]------(green test lead)-----<15 ohm resistor>-----(black test lead)------[metal cluster case]

[metal cluster case]-----(another black test lead)------[negative battery terminal]


To put two resistors in series you can just twist their leads together and treat it like a single resistor. Just be sure nothing else makes contact with the intermediate connection between the two. Or as an alternative, you can use an additional test lead to join the two together.

Like this:

[sender terminal on gauge]-----(green test lead)-----<15 ohm resistor>----(another green test lead)----<another 15 ohm resistor>-----(black test lead)-----[metal cluster case]

So with that I tested things out. Starting with trouble figuring out which post is the +12v terminal and which is the sender terminal. First try was on the fuel gauge. I thought the tab to the left was the +12v terminal so thats how I set it up and it ended up pegging out at full.

Looked like this

[msg]

So I tried switching the red/green tab connections and this got a reaction as Ray described. I have the 15 ohm resistor in place to test to see if the gauge reads to half full and it did!

[msg]

Then connecting another 15ohm resistor in line to test for full

[msg]

Then I tested the temp gauge with the 15 ohm resistor in place for hot temp and it worked

[msg]

Then I had a resistor of a higher value that I cant remember exactly the range but it was high enough to discharge a camera battery capacitor years ago. I replaced the 15 ohm resistor with it and the gauge went to cold.

[msg]

The battery gauge (ammeter) I tested next and I may have a dud or Im not following instructions properly. I did a direct connect to the tabs of the gauge and tested with both polarities and nothing happened. I did actually make contact with the leads to the battery off camera, couldn't get the pic and do both. I also tried the 12 volt battery and it did move the needle some with each polarity switch. It didnt peg out it only moved almost a notch in each direction.

[ray_mcavoy]

Cool! Looks like your fuel & temp gauges are okay.

Sounds like the batt gauge (ammeter) might have some issues though. There are three 1/4" hex head shetmetal screws that hold the temp & batt gauge assembly into the cluster. If you remove those, you can pull the backing plate that holds both gauges out through the back.

Then take a close look at the wire coil on the back of the batt gauge. Sometimes they get overheated due to connection problems in the truck's wiring that allow too much current to flow through the gauge. That usually results in a darkened / burnt / discolored look of the coil itself and sometimes even the surrounding parts.

[msg]

Thanks Ray, the speedometer checked out too. Drill in reverse mode when triggered had the speedometer moving as it should. I took some pics of the ammeter and I guess its time to spend $65 or so for a replacement.

[msg]

For the oil pressure test I do have a regulator thats on my paint gun and the pressure coil with fittings I bought as a replacement. Is it best to buy some additional parts and not use the replacement line and fittings? I didnt know if I were to use the connectors and fittings on that line if it would mess up the line when I finally get things ready to install it.

[ray_mcavoy]

Yeah, that ammeter looks like it's well done

The truck's wiring connects the ammeter in parallel with the main feed / charge wire that runs from the positive battery terminal, across the radiator support, to the bus bar (2 screw terminals) on the horn relay. So that main feed / charge wire serves as a shunt for the ammeter. And the shunt wire normally caries nearly all of the current with only a small fraction taking the parallel path through the meter itself. But in the event of a bad connection at either end of the shunt wire, all of the current tries to go through the meter, causing damage like you're seeing there. Sometimes the black & black w/white stripe wires that connect the ammeter get damaged due to excessive current too. To prevent that from happening, I recommend adding a couple of 4 amp inline fuses to those wires like GM did in the 67+ trucks. Put one fuse in the black wire that connects to the "batt" terminal on the starter solenoid, and the other fuse in the black w/white stripe wire near the end that connects to the horn relay.

Edit: just saw your post on the oil gauge. Once you install the compression fittings onto the line, they can't be removed again without damage. But the line / fitting assembly can be connected, disconnected, and re-connected to the gauge a few times as long as you're careful not to over-tighten the fittings. You might also want to double check to make sure you have the correct fittings. The originals used special compression sleeve nuts (Weatherhead #6100x2 or equivalent) where the ends of the nuts have a built-in compression ferrule. The ones you have pictured appear to have separate ferrules ... they might still work, but it would probably be a good idea to make sure they thread into the back of the gauge okay before permanently installing them onto the line.

[msg]

Thanks for the tip on the fuses to protect the ammeter purchase Ill be making. I have an American Autowire wiring harness kit that replaces the old stuff. I dont know if they have made any correction to the problem but I will look into it. I can give them a call.

As for the oil pressure line, I bought it from Classic Parts assuming it was what I needed

https://www.classicparts.com/1947-77...ctinfo/24-781/

Ill look around for the original I took off in the garage at least for a test hook up. I did take the fitting out of that plastic bag and it does thread into the gauge. If I can figure out what size thread fitting that is I can buy another fitting I guess that is a step down from the 1/4 inch air hose I have and connect it to the air hose and through the regulator for a test.

[msg]

I found the piece that connects to the gauge and extended just out of the firewall. I bet the other portion was tossed. I removed this so long ago I forgot it wasn't an all in one line like the replacement I bought.

[msg]

I was hoping to cobble together something to test the oil pressure gauge with and found my brake line fittings kit. The size of the fitting I would need for the existing oil line connector looks like a 3/8-24 and the air gun regulator is 1/2-20.

I have been looking online for a 3/8-24 male to 1/2-20 male adapter and cant find one. Is there another part or setup that might work?

The type of part I thought to look for would look something like this

https://www.summitracing.com/parts/w...saAsaSEALw_wcB

[msg]

here is a pic of the parts I was tinkering with to get the fitting and thread sizes figured out

[ray_mcavoy]

Originally Posted by msg

Thanks for the tip on the fuses to protect the ammeter purchase Ill be making. I have an American Autowire wiring harness kit that replaces the old stuff. I dont know if they have made any correction to the problem but I will look into it. I can give them a call.

AAW offers a few different harnesses. Their OEM restoration harnesses are direct copies of the originals and probably won't include the fuses. And I don't think their Classic Update kits even support the factory ammeter.

Originally Posted by msg

I found the piece that connects to the gauge and extended just out of the firewall. I bet the other portion was tossed. I removed this so long ago I forgot it wasn't an all in one line like the replacement I bought.

Yeah, that looks like it should work for testing purposes. Although the fitting on the far end of that line looks a bit different than the union that I've seen on most of the factory 2-piece oil lines so I'm not entirely sure what type of thread you'll need to adapt that over to your air regulator. The threads on the regulator are likely NPT (probably 1/4").

[msg]

The wiring harness kit I purchased is this one

https://www.summitracing.com/parts/AWW-500560

Ill call AAW tomorrow and see what the say about the factory ammeter, although in replacing the ammeter I am thinking to get this one. I dont know if its factory specs or updated I would think.

https://www.classicparts.com/1964-66...ctinfo/24-747/

I was able to make a 1/4" line with some fittings from the kit I had and test the oil pressure gauge and it was pretty close to the 0-60 as I tweaked the air regulator! So all seems good there.

[ray_mcavoy]

I'm glad to hear the oil pressure gauge checked out okay.

Yes, check with AAW to be sure, but I don't think their Classic Update wiring (like the one you purchased) support the factory ammeters.

The replacement ammeter from Classic Parts you linked to appears to use an updated style of meter movement / coil assembly. However, it would still function the same as the original and require the same wiring configuration. So I'd recommend holding off on buying that until you hear back from AAW. And if you do have to change over to a voltmeter, check with fellow member TBONE1964 ... I know he offers voltmeters to retrofit into the 67-72 gauge clusters and I believe he makes them for 64-66 too.

[msg]

I checked with AAW on the kit I bought and the ammeter cannot be used at all. I was told to get a voltmeter instead from Classic Instruments, LMC, and the like just to be sure its a voltmeter and not an ammeter.

[msg]

Hey Ray, I bought a voltmeter and wanted to test it. Is it as simple as a 12 volt battery like one for a fire detector hooked up to pos and neg? I bought this one here and plan to retrofit it into the cluster I have but to look more OEM.

https://www.ebay.com/itm/Automotive-...IAAOSw-11Zy9Ss

[ray_mcavoy]

Yes, you can test that voltmeter by hooking it up to any 12V battery.