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My 66' Toronado has an ammeter that isn't working. I'm currently in the process of refurbishing my instrument panel due to the flaking wrinkle paint so I thought I'd take the opportunity to troubleshoot why my ammeter isn't functioning.
I double checked the car wiring. and, fortunately, verything is hooked up correctly. The ammeter is connected to two wires at the instrument cluster, one red and one black with them connected across a "shunt" wire as shown in the wiring diagram. Note that the wiring diagram depicts the inboard gauge cluster incorrectly. They show a Tan and Black wire. It is actually a Red and a Black. In this car, the ammeter acts almost like a millivolt meter rather than your standard ammeter where all the current runs through the gauge. Only a very small proportion of current runs though the gauge.
I rigged up a very cheap and basic adjustable power supply and used my cars radio light as a load. In the beginning, it didn't work but after fiddling around with it I noticed it came to life. I suspect a couple things. First, those pins on the circuit board may be slightly loose. Second, some oxidation may have started to affect the circuit. We're talking milliamps and millivolts here, it wouldn't take much to interfere.
So take a look at the picture attached. With the power supply cranked up to 11v, with 280 mA running through it and the lamp brightly lit, you can see the ammeter is showing a discharge. God only knows if the gauge is accurate or not but at least I know I have some movement. It would be very good to know what a known good gauge would show, or even some kind of spec.
I started it with 0.5 volts and slowly worked my way up to 11 volts.
Last edited by ourkid2000; November 21st, 2023 at 12:14 PM.
Where did you find the physical termination of the red and black wires from the ammeter? I'd like to troubleshoot mine as well but could not find the "tan"/red wire.
Where did you find the physical termination of the red and black wires from the ammeter? I'd like to troubleshoot mine as well but could not find the "tan"/red wire.
Great question, however, it's pretty impractical to try to track down that info on my car without tearing everything apart so I took the easier/simpler route. I just disconnected the connector on the back of the panel and checked the continuity to the horn relay junction block on each wire (the read and the black) individually. That will at least tell you that things are hooked up correctly. The last thing to try would be to ensure both wires can light an incandescent test light. If it meets those two conditions, I'm confident in that the system is up to the job. Both wires passed the test.
I guess the red wire would be connected to the legendary "shunt splice" that no one has successfully found, LOL. The black wire would be connected to the fusible link wire at the junction block. or maybe the other way around......who knows. Maybe I'll have a good look at the wires going to the fusible link splice and see which ones are there. It's all buried under the A/C plumbing so it's really hard to see what's going on.
Last edited by ourkid2000; November 22nd, 2023 at 08:15 AM.
Gchecked the continuity to the horn relay junction block on each wire (the read and the black) individually. That will at least tell you that things are hooked up correctly. The last thing to try would be to ensure both wires can light an incandescent test light. If it meets those two conditions, I'm confident in that the system is up to the job.
True. My curiosity about this comes from the obvious question "why did it stop working if all of the components and connections seem in order?"
Since we are dealing with millivolts and milliohms, anything other than perfect connections could affect the resultant sensitivity of the ammeter. I'd guess the component with the best conductivity is the continuous piece of wire to which each end of the ammeter is connected. At the horn relay it's in the same crimp (at least on my 66). Any resistance between the two wires in that crimp (again on the order of milliohms, which is not at all unusual to find in fresh connections!) could cause issues. Being accessible, some acid flux and soldering could improve that. At the other end, the shunt splice, I'd assume there's also a crimp that could be soldered if it could be seen. Since we can't visually inspect it, focusing on what we can is the next best thing. As you said, the connections at the ammeter itself need to be clean and as conductive as possible. Just my ponderings.
EDIT: What is the current (or voltage, either would be informative) required for full deflection of the ammeter by itself in each direction? We could reverse engineer the conditions/etc needed to make it work and consider where they might be wrong.
Last edited by mike 66 toro; November 22nd, 2023 at 09:04 AM.
EDIT: What is the current (or voltage, either would be informative) required for full deflection of the ammeter by itself in each direction? We could reverse engineer the conditions/etc needed to make it work and consider where they might be wrong.
I wouldn't want to run too much through it but based on what I saw I'd bet an amp would probably get full deflection, roughly.
The last time I had the instrument panel out of the car, I swapped in a spare gauge that I had on hand because my original ammeter wasn't working. I actually have a full spare instrument panel that we got from a scrapped Toro years ago. The ammeter still didn't work, unfortunately, so I thought I definitely had a wiring issue.
When I removed the panel from the car a couple days ago, I removed that spare ammeter to test it out on the bench. Anyway, that thing is completely dead. It passes current and the test lamp will light but the gauge doesn't deflect. That's when I tested my car's wiring, which tested fine. So, that's also when I realized I probably had a connection issue at the gauge itself.
When I tested the original gauge on the bench I initially had an open between the two pins for the ammeter. Then suddenly I had 80 ohms......and so on so I could tell the connections were wonky. After cleaning everything up I figured I'd give it a go with the power supply and a test light and sure enough, it came to life. It's too bad I can't verify it because I don't really have a known good gauge. I'm not sure but I don't think any of the other Olds from '66 had an ammeter, rather they used a dummy light, so there's not much out there to check against.
I can definitely play with the dead gauge a bit though and see what I can find out. Maybe I can find the failure point on these things
Last edited by ourkid2000; November 22nd, 2023 at 12:04 PM.
In the beginning, it didn't work but after fiddling around with it I noticed it came to life. I suspect a couple things. First, those pins on the circuit board may be slightly loose. Second, some oxidation may have started to affect the circuit.
Do you think you've fixed something? Percussive maintenance? Or did you mean fiddling with your connections? I'm anticipating you plugging it in temporarily and pulling on the power windows switches.
Do you think you've fixed something? Percussive maintenance? Or did you mean fiddling with your connections? I'm anticipating you plugging it in temporarily and pulling on the power windows switches.
I believe I had a bad connection from one of the pins up to the ammeter. Just disturbing the pin with my test harness contacts got it working again. That's what it looks like anyway. I'm going to reinforce all the pins using a great method I found here:
Do you think you've fixed something? Percussive maintenance? Or did you mean fiddling with your connections? I'm anticipating you plugging it in temporarily and pulling on the power windows switches.
Hooked up a spare headlight to my little test rig today. At around 2V the headlight is flowing roughly 1 amp and the ammeter was just about at full deflection. I guess I was pretty close with my prediction earlier. God only knows if this ammeter is working correctly so it's too bad my spare one is completely dead. I'll look into trying to get it working. I'll do up a little thing with pictures, etc over the coming days.
At least you know it will do something. I wonder how much has to be flowing through the shunt to get full deflection.
I managed to get the spare ammeter working last night. It's slightly different as it goes to full discharge deflection at 1.5 amps and you have to go quite a bit higher to get it to full deflection on the charge side. The needle doesn't return to center once you remove power though so there's definitely something messed up internally. Base on this I'm pretty confident that 1 amp, roughly, is full deflection.
I will temporarily slave in the ammeter and try the windows as I have measured mine to be pulling well over 10 amps when operating the drivers side power window. Just gotta be careful having the power on with the instrument panel removed.
Do you think you've fixed something? Percussive maintenance? Or did you mean fiddling with your connections? I'm anticipating you plugging it in temporarily and pulling on the power windows switches.
Tried this today. No deflection on the ammeter when I operated the windows. I'm a bit lost at this point really. Here's what I've done so far:
- I've bench tested the ammeter and it does operate although I'm testing it without any kind of specs. When about 1A flows through the meter, I get good deflection.
- I took the cluster connector, disconnected it from the ammeter, and tested the black and the red wires (the wires connected to the ammeter) for continuity to the 12V junction block under the hood. I have continuity on both.
- With the connector disconnected and power applied, both pins light an incandescent test light.
- I have a second ammeter, it behaves almost exactly the same. The only difference is that it doesn't center itself after power is removed. It's malfunctioning but still works on the bench.
Man o man, I could sure use some help on this one. I've put a lot of work into this and am getting nowhere! As far as I can tell, I have a completely intact system in my 1966 Toronado yet my ammeter simply doesn't function. If anyone could review what I've done here and maybe offer any suggestions, I sure would appreciate it.
If the chassis service manual wiring diagram is at least half right, it should operate like the way I've redrawn it below. Note that my car has a fusible link, even though the '66 CSM doesn't depict it. The wire colors in the CSM are incorrect. It says I should have a blk/wht wire and a black wire coming from my ammeter. This is incorrect, I have a blk/wht and a red. I had previously thought that the blk/wht wire was a solid black until I flipped the connector over and found the white stripe......blk/wht it is.
Note the colors. This is the inboard instrument cluster connector that attaches to the ammeter.
So I disconnected the harness from the junction block to see what I would find in the harness (wire color that is):
At the fusible link, in the above picture, I have a thick red wire and a blk/wht wire. The thick red wire should be the shunt, if the wiring diagram is correct. The ammeter, in the Toronado's case, would be reading the voltage drop across the shunt as long as the red wire from the ammeter is connected to the "shunt splice" and displaying it as either charging or discharging. Well, with the fusible link removed from the junction block, both the red pin and the blk/wht pin on the back of the ammeter have good continuity to the fusible link ring terminal. I tested them before with an incandescent test light, which lit brightly, as well so the connections are solid.
As I mentioned before, I bench tested the ammeter and it seems to respond to about ~1.5A for full deflection but who knows if that is even the right spec? I have a second ammeter from a parts car that behaves very similar so that's decent data at least. Note that I believe it is impossible to measure the shunt resistance directly with my equipment as the resistances that you're measuring are too small for the typical meters we all have. Unless someone has a workaround figured out to measure it?
Anyway, if anyone has any other ideas I'd love to hear 'em. I was thinking about slotting in my DMM in ammeter mode to the cluster connector ammeter connections to see if it does anything, when I operate the windows or headlights but I have to give that a little thought before I try it.
I literally never have seen a GM vehicle with a working ammeter, so I remain unconvinced that there ever existed such a thing. With the ammeter disconnected and some heavy loads operating (blower, windows etc), do you read any voltage between the two wires? It'll be millivolts likely. I have a few ideas how to make it work.
Last edited by mike 66 toro; January 14th, 2024 at 04:46 PM.
When I say I have some ideas how to make it work: If we look at the voltage present across the ammeter leads with the meter itself disconnected, we can determine what it will take to tweek the ammeter to respond to that. Let me know what you find.
When I say I have some ideas how to make it work: If we look at the voltage present across the ammeter leads with the meter itself disconnected, we can determine what it will take to tweek the ammeter to respond to that. Let me know what you find.
Not a bad idea. My Fluke can read mV pretty accurately, I'll rig it up today and post what I find.
When I say I have some ideas how to make it work: If we look at the voltage present across the ammeter leads with the meter itself disconnected, we can determine what it will take to tweek the ammeter to respond to that. Let me know what you find.
With power disconnected:
Leads connected to ammeter pins, ammeter cluster connector disconnected, car battery disconnected. *edit* this voltage reading was the same when the battery was connected and no courtesy lights were running (door closed)
Battery connected:
Leads connected to ammeter pins, cluster connector disconnected, car battery connected. Note, courtesy lights are running because the door is open.
I noticed that the voltage changed from 0.1 mV to 26 mV when the courtesy lights came on as I opened the door. Watched it change as I closed and opened the door.
Battery on, key on:
Leads connected to ammeter pins, cluster connector disconnected, battery on, key set to "on" and windows operating. The mV were the exact same numbers when window is operating or not. No change under load. A little strange when you consider that the courtesy lights seemed to affect the voltage on the meter and that's a relatively light load.
Last edited by ourkid2000; January 15th, 2024 at 08:08 AM.
I had a working ammeter the whole time (well at least after I had repaired it on the bench), it was my testing methods that were incorrect! The clue that turned me on to the problem was where I wrote above that the courtesy lights affected the voltage at the ammeter but the power windows had no effect. That got me thinking......
If you look at the wiring diagram, you can see that only the power window relay would have an effect on the current shunt. The actual electrical draw for the power window motor is outside of the shunt! It uses the circuit breaker right off the junction block for power and circuit protection. The actual current flow when the windows are operating never goes through the shunt. I used the headlights as a load instead......working ammeter!
I posted above at the start of the thread that the ammeter wasn't working originally, and it wasn't, so this really threw me for a loop. The connections were intermittent and I fixed it on the bench. When I put it in the car, it was actually working but I had inadvertently used a testing method that just happened to be completely flawed. Crazy, oh well. The needle deflects about a needle's width to the D side with the headlights on just running off the battery. Is it right? I don't know but at least it's something.
Last edited by ourkid2000; January 15th, 2024 at 09:39 AM.
Lol that's awesome. I guess we should have considered that the test methodology was flawed! Even if the scale is off, at least you know that deflection toward D means discharging.
When running with no loads, does it move toward C ?
Lol that's awesome. I guess we should have considered that the test methodology was flawed! Even if the scale is off, at least you know that deflection toward D means discharging.
When running with no loads, does it move toward C ?
I don't know if I want to start the car with the instrument panel sitting on the steering column. I think I'm gonna live dangerously and just reinstall the panel. There's movement on the gauge so I'm happy enough with that.
I don't know if I want to start the car with the instrument panel sitting on the steering column. I think I'm gonna live dangerously and just reinstall the panel. There's movement on the gauge so I'm happy enough with that.
Yeah it is quite precarious. I was going to do these tests on mine but I've had enough of the instrument panel for a while
I wish I could help and I'm sure glad I didn't buy a Deluxe model, I have a 66 base model and it's enough for me!
I'm marveling at the colored wireing diagram, where did you find it? can you direct me to it or post it in it's entirety?
It would help my old eyes track down a problem with the taillight issue.
Just my opinion, ammeters are dangerous fire hazards. If there is a way to install a replacement volt meter do that. Trying to repair the ammeter is a fools errand. There is a reason modern cars don't have an ammeter.
Just my opinion, ammeters are dangerous fire hazards. If there is a way to install a replacement volt meter do that. Trying to repair the ammeter is a fools errand. There is a reason modern cars don't have an ammeter.
The more modern type of ammeter scheme found in these cars has the "shunt" under the hood. So the high current isn't entering the passenger compartment like on earlier cars, think 50's and earlier. So in the toro, the ammeter is essentially measuring the small voltage dropped in the wire under the hood. The old (and yes, pretty hazardous) systems had full amperage running to the dash gauge and were a terrible idea! On the toros there is only a tiny current, maybe 1 amp, going though the ammeter. In any vehicle, new or old, a Voltmeter is in my opinion much better.
Last edited by mike 66 toro; January 15th, 2024 at 09:25 PM.
The differences between Standard/Base model and Deluxe are cosmetic, mostly interior, so no effect on your taillight (or other functional) problem.
I believe the colored wiring diagram came from the Chassis Service Manual, but note the comments earlier as to inconsistencies of colors in the schematic drawings compared to what is seen in the actual cars.
I wish I could help and I'm sure glad I didn't buy a Deluxe model, I have a 66 base model and it's enough for me!
I'm marveling at the colored wireing diagram, where did you find it? can you direct me to it or post it in it's entirety?
It would help my old eyes track down a problem with the taillight issue.
The differences between Standard/Base model and Deluxe are cosmetic, mostly interior, so no effect on your taillight (or other functional) problem.
I believe the colored wiring diagram came from the Chassis Service Manual, but note the comments earlier as to inconsistencies of colors in the schematic drawings compared to what is seen in the actual cars.
Also, there are errors in the '66 wiring diagram particularly in the tail light system. Have a look at the wiring, post rear body connector going aft. You can figure it out once you look at it for a bit but at first it's a bit confusing.
Just an update to this. Installed the instrument panel today and started the car. The ammeter is working perfectly once again. I'll post some pictures of the restored instrument panel shortly.
Re-did the wrinkle paint finish on my instrument panel. I am really happy with the results. The picture doesn't really do it justice, hard to get the lighting right on my phone cam but I must say it looks spectacular. Very satisfying to finish this up finally.
Nice! I'm waiting for my radio to get back from repair - oh, and that whole top end motor rebuild to be completed lol - before I swap in my restored cluster. Yours looks terrific!
November 21st, 2023, 11:53 AM
