ammeter going crazy

[EB Passed down]

I just installed Wild Horses 1in. body lift, which went very slick compared to the horror stories i've heard. Now after hooking my battery back up, my ammeter ticks from 1 max to the other even with the key off. I can already guess I pulled or stretched something but I have no idea what. I've gone through and installed new grounds to the block, to the body to the frame and to the alternator. I'm curious if there is a likely culprit others have run across before. Thanks

 

[DirtDonk]

Well that's a new one... Normally like you say you run into all sorts of trouble taking the old body mounts off, but in this case I guess your Bronco just wanted you to know it wasn't going to take it lying down that you got past that drama.

I'm thinking we can't rule out that it could just be a coincidence that it happened at the same time. But I hate assuming coincidences.
Of course, it could be both! Just coincidentally messed up your alternator when you did the body lift? The fact that it's doing it with the key off means it's something that is actively flailing around without a spinning alternator. But it could still be a bad diode in the alternator.

What alternator and regulator are you running? Can you feel anything going on with the regulator? If it's an old style, is it clicking? Any style is it warm or hot just sitting there?
Is there power to the Green w/red wire in the regulator's connector with the key off?

Won't hurt to pull a few fuses, just to see if it goes away, but if not then maybe disconnect the battery, then the alternator, then reconnect the battery to see what happens.

Good luck. Definitely report what you've done and found. This isn't the normal body lift discussion that's for sure!

Paul

 

[DirtDonk]

Oh, and until you find the culprit, I'd keep a close eye on your battery's charge. If it looks like it's discharging, you should disconnect it at night or when you're not driving it for awhile.

Until you fix the issue.

Paul

 

[Joker11]

depending on how fast it is swinging from one extreme to the other might help finding it.
If it is a self resetting type of circuit breaker, it would be slower, I imagine.

I like the idea of the bad diode in the alternator rectification. But I would imagine that it would peg one way. Usually a diode will bias one way, not usually back and forth. But I suppose anything is possible.

An old turn signal flasher module is just a bimetal strip that heats and cools quickly enough to blink the lights. Could be blinking the ammeter.

Just throwing out some ideas. Nothing technical. Not well thought out. Just brainstorming here.

 

[EB Passed down]

Thanks, I loving being unique. I have disconnected the alt. from the bronco harness and it's still there. I disconnected coil, alt. and the tach, no change. When I disconnect the hot lead from the starter solenoid to the ignition it goes away. I'm thinking that disconnecting that lead eliminates too many things at once to really narrow it down. I'm wondering if it's a bad ground or a hot lead getting grounded? What else would make that ammeter jump?

 

[EB Passed down]

It swings fast. I can't be sure but I'd swear it snaps down or negative and rebounds all the way to max positive.

 

[DirtDonk]

Problem with some old gauges too, is that the needles lose most of their dampening, so even if it's only a couple of amps being pulled, the needle could swing wide like it's pulling 40 amps or more!

By pulling the main lead at the starter relay, it's not just that you're eliminating a lot of circuits, but you're eliminating the source of the power too. No battery power at all, means no swinging needle.
But at least it's a start! Keep pulling things.
Maybe reconnect the battery and disconnect the voltage regulator.

Any relays hooked up independently? Headlights maybe? Stereo? Something we're not thinking of?

Paul

 

[Joker11]

I am not familiar with the function of these ammeters. But the ammeters I am familiar with are called shunts.

Basically, all the current has to go through the shunt and then out to everything. This is usually why people don't like them. All the current has to go through the dash and back. This can cause unwanted voltage drop as well as a fire hazard from all that current either heating up old worn out wires or by shorting out directly.

The shunt is basically a bar that looks like brass and solder (it's actually a manganin alloy). It is a known value resistor that is connected in series, not parallel to the load. Then the voltage across the shunt is measured. Since we know the value of the resistor, we can calculate the amperage. It's Ohms law. The bar is rectangular and they use a file to file down a notch until they get exactly the amount of resistance in it. Kind of like kinking a water hose until you get the flow of water you want. Ours at work are rated at 50mV at 600 amps. So if we measured 50mV, we should be seeing a amperage load of 600amps. It should be linear, so at 300amps, you would see 25mV. and such. does that make sense?

If the ammeter in the bronco is made that way, you might really have an issue if it is pegging on the extreme high side. Because that would mean you are dropping full amperage somewhere. But where?

I say, plug it all back in. start pulling fuses. narrow it down. You already eliminated the alternator if you completely disconnected it. It's going to be something simple when you find it. smack your forhead and laugh type of thing, I am sure.

 

[EB Passed down]

The voltage regulator is part of the alt harness I disconnected, so that's already ruled out. This weekend I think I will hook the battery back up and start pulling fuses. There aren't too many in a Bronco. I don't know about any funny independent wiring issues. I have it a long time but my dad did who knows what back in the day to keep it going.

 

[DirtDonk]

The EB ammeters are fairly clever in design I think. If Ford had simply sprung for some larger gauge wire in the charge loop, we'd be sitting pretty even for upgraded alternators and fairly safe.

Unlike a shunted version, ours are somewhat "direct reading" as the wire does run through the firewall and to the gauge and then back out to the battery (in an over-simplified version that is) but instead of a gauge that splits the wire in two and reads what passes through, it's inductive instead.
There's a small loop on the back of the ammeter and the charge/power wire simply passes through it without break. Much safer than a direct connection type, but less efficient probably than a shunted type. Like you said, all that extra 10ga wire leads to potential voltage drop and more potential for problems. Amazing that they have worked so well for so long, but they have.

I shouldn't say they don't have a break in the wire, as not far from the gauge there is a large push-connector splitting the two halves of the circuit. It's pretty robust and reliable, but still can be subject to corrosion and more voltage loss and heat. Definitely worth inspecting every few years to make sure it's clean and tight.

Paul

 

[DirtDonk]

The voltage regulator is part of the alt harness I disconnected, so that's already ruled out...

How's that? Did you disconnect the alternator's main charge wire from the backside of the alt? Or did you pull the 3-wire plug down by the battery? Or did you pull the 4-position plug off of the regulator?
Reason I ask is that, if you didn't pull the main charge wire off of the alternator or unplug it's connector, it's still connected. Regarding the regulator, the Yellow wire is directly spliced into the last wire you pulled off of the starter relay. So even with the alternator disconnected, your battery is still feeding power to the voltage regulator.

Sorry if I'm missing something. The '72 might have a slightly different layout with regard to the main plugs, but the fact that the regulator is powered by the battery directly off of the Black w/red wire on the battery side of the starter relay, that component may still have had power to it until the end.

Paul

 

[Joker11]

I see. So the coil, when powered, induces a magnetic force that then moves the needle.

 

[DirtDonk]

Yep. Just like your clamp-on inductive timing light on a spark plug wire.

Man, that brings back memories. I was so glad when I got my first inductive light and didn't have to unplug a spark plug wire and connect the timing light's interface between the plug and wire. No more fiddly connections and much faster. Viva la technological advances!

Paul

 

[EB Passed down]

I'll have to double check in the daylight, but I believe the 3 wire plug by the battery disconnects the alt. and the regulator. I did also pull the 4 wire plug from the regulator. I can't remember if it makes a difference, but I'm running the 89 Crown vic starter solenoid. I'll also check that plug. Is that the plug that you need to undo to remove the ammeter?

 

[DirtDonk]

Yes. The one under the dash is right near one of the major junctions and has that one wire come outside of the main harness tape and is free and clear to play with right next to the back of the ammeter.

Usually that is... One guy went looking for his a year or so ago, and found it way outside of the normal range. But so far that's the only one I know of that was not easy to get to.
A quick peek under the dash will usually find it.

Paul

 

[EB Passed down]

I checked the ammeter plug in before work today, it was connected and tight. I guess I'll start pulling fuses to narrow it down.

 

[EB Passed down]

Pulled every fuse and it still ticks. I just left the battery on and started touching and feeling everything under the dash. The power lead to the headlight switch was hot. I unplugged the switch and it was really hot and the tick went away. First question, Should there be more than 1 spot hot on the back of that switch when the lights are off and key is off? Do you think the switch could go bad inside passing current getting hot and be my only problem? or is the problem down the line somewhere? No lights are on.

 

[Joker11]

the headlight switch is dual function.
It is on and off for the headlights.

It also has a resistor in there that dims the dashlights. I would twist the dimmer and see if anything changes. But then replace the switch anyways.

 

[EB Passed down]

I think I'll pick 1 up from Napa tomorrow and see.

 

[DirtDonk]

Sounds like a short-circuit was causing the internal breaker to open and close. Every time it would close, the short would show as a drain on the ammeter. Every time it would overload and open, it would swing back to zero, but perhaps past zero towards the positive because of needle flutter.
Or if the engine was running it would certainly show an alternating charge and drain too.

Sounds like you certainly found a culprit. But you still have to find the actual short. If it's in the switch, bingo, you're done. If it was one of the wires though, you're still on the hunt.

And remember, the light switch, along with it's "normal" and expected duties (the lights) also powers the brake light switch and the horn.
The switch gets it's main power directly from a splice into the main Black w/yellow ammeter wire, and dispenses it out directly to those other components without a fuse. All protection for the horn and brake lights then, is also using that thermal circuit-breaker inside the switch.

Paul