lights/power/voltage drops

[Previologist]

I'm still working through your previous post for now. I got my analog meter working (bad fuse) and it has a 10v option but I haven't used that range yet. From your previous post

So with that current being drawn, measure the voltage across that 100A link with a small range (couple o' volts) if you have it, 20V if that's the smallest available. Shouldn't be more than say 1/4 - 1/2 volt tops, and I would hope a lot less. Then, to double-check - and use a different meter range - set the meter to 20V, then with the black on ground, touch the red to one, then the other side of the 100A link (14ish volts presumably). Then, take the difference between those two values to get the voltage across the link. Should be around the same as across the link, but the meter may not be all that accurate at very low values. If you can have the idle up a bit, that's more realistic, but not entirely necessary.

So I'm still confused here because to my understanding the alternator SHOULD be throwing 14+ volts back at the battery through that 100 amp fuse. Am I wrong? (it may be the stuff underneath that is throwing a wrench in my understanding, so will study your blowup a bit more). I got a 15v reading across the 2 screws on that fuse with my digital (head and brakelights on), and just now I tested each side to ground with my analog and saw no detectable difference/loss, both sides showed near 15v. But unless I misunderstood, you are telling me there should only be a tiny voltage across it to begin with. So I want to get this possible misunderstanding cleared up so I'm less confusable.

I'm going to have to digest your last post a bit before moving on it, but I think I understand what you're getting at

[man_btc]

Yes, the alternator supplies voltage to the battery - higher than the battery's voltage on its own - in order to charge it. (The battery also "smooths out" variations in the voltage from the alternator in somewhat the same way that an air tank smooths out the pulses from an air compressor.)

I'm confused about the measurements. One of those fuse block screws bolts to the alternator wire's o-ring. The other screw bolts to metal that bolts to the battery positive clamp. The 100A fusible link has two tabs with holes that those screws bolt through, so they should be electrically connected through it, meaning there should be a near-zero resistance and near-zero voltage change across what is a short piece of metal. That's consistent with measuring the voltage on either side to ground being the same, because if one side is 15V and the other side is 15V, there can't be a 15V difference between them.

The larger investigation here is to find where the voltage across the headlights is being reduced - the voltage across the headlight terminals is too low because of one or more of these:

• Not enough voltage is being applied at the source (the alternator)
• Something between the alternator and headlight positive terminal (that the alternator/battery connection ultimately connects to) is "using up" too much voltage
• Something between the headlight's negative terminal and ground (which it ultimately connects to) is "using up" too much voltage.

An rough analogy might be two sprinklers being fed by a faucet and a "Y" connector. You run one (the headlights), then when you run the second (the brakes), they both lose pressure. Can you open the faucet to increase the water pressure? That's the alternator increasing it's output when it detects the voltage go below what it should be. On the other hand, what if you turn the faucet but nothing happens - maybe there's a problem with that "Y" connector, or the faucet knob is turning but it's not opening the valve (alternator electronics), there's a kink in an extender hose (wiring) that runs from it to the faucet, or a clogged screen somewhere restricting water flow to both sprinklers - that's kind of where we're at.

Maybe see if you can jam the positive (red?) multimeter probe into the back of the smaller connector under the fuse block - pin 1, which is probably the one closest to the front of the van with a white/blue-stripe wire. That's what's delivering the voltage out of the fuse block to the headlight relay. With the other probe (black?) on ground and the meter set to 20V DC you should see a voltage that's really close to the voltage at the battery. If you see that drop more than a small fraction of a volt when the lights+brakes are on vs just the lights, something in that fuse box is blocking the extra current needed for both. If it stays essentially the same as the battery voltage, it's time to look elsewhere.

[Previologist]

Yes, the alternator supplies voltage to the battery - higher than the battery's voltage on its own - in order to charge it. (The battery also "smooths out" variations in the voltage from the alternator in somewhat the same way that an air tank smooths out the pulses from an air compressor.)

I'm confused about the measurements. One of those fuse block screws bolts to the alternator wire's o-ring. The other screw bolts to metal that bolts to the battery positive clamp. The 100A fusible link has two tabs with holes that those screws bolt through, so they should be electrically connected through it, meaning there should be a near-zero resistance and near-zero voltage change across what is a short piece of metal. That's consistent with measuring the voltage on either side to ground being the same, because if one side is 15V and the other side is 15V, there can't be a 15V difference between them.

There isn't. I get DC 15v reading when I place one probe on the battery side screw of the alt fuse and 1 probe on the alternator side screw of the alt fuse. I don't understand why you think I should only be getting a fraction of a volt.

So with that current being drawn, measure the voltage across that 100A link with a small range (couple o' volts) if you have it, 20V if that's the smallest available. Shouldn't be more than say 1/4 - 1/2 volt tops, and I would hope a lot less.

Did you mean a LOSS of 1/4 to 1/2v?

[man_btc]

There isn't. I get DC 15v reading when I place one probe on the battery side screw of the alt fuse and 1 probe on the alternator side screw of the alt fuse. I don't understand why you think I should only be getting a fraction of a volt.


Did you mean a LOSS of 1/4 to 1/2v?

Yes, the voltage "drop" or "loss" is the reduction in voltage across a good metal conductor, which should be tiny. You should only see large differences in voltage across things that are either supplying large amounts of energy (a battery) or absorbing large amounts of energy (lights, fans, wiring that's heating up).

[man_btc]

Looking back at your pics I see the difference between your fuse box and mine, primarily that your battery connection doesn't have an integral metal piece sticking out to the battery plus terminal and yours has an additional "ALT-S" fuse where mine has none. Meaning your alternator has a fuse to protect the circuitry inside it that increases the alternator power (when it sees the voltage start to decline over that "ALT-S" connection when more electricity is being used). Check that ALT-S fuse to see if it's got continuity.

It would make a lot more sense (no pun intended - that's what the "S" stands for) to find the alternator is supplying enough voltage and current initially but when additional loads come on line it's not increasing it's output enough to compensate. Although that wouldn't explain why with a lot of stuff drawing power, the voltage didn't drop at the battery when the initial tests were done.

[originalkwyjibo]

Hi Previologist. Your info lists the PNW as one of your locations. Are you currently there and what part of the PNW? Maybe I can assist in person. PM me if you prefer to maintain privacy.

[Previologist]

Hi Previologist. Your info lists the PNW as one of your locations. Are you currently there and what part of the PNW? Maybe I can assist in person. PM me if you prefer to maintain privacy.

Oh that. That was from my younger, wealthier days when I did a lot of roaming around and Previa camping. But thank you for the offer! I used to visit the PNW every year, and I still try every year, but I haven't been there since 2020. Of course the PNW is on my to-do list for this year as always...but will it happen?

As for my problem, my plans to head for the SW just firmed up and I don't think I'm going to have any more time to worry about this before I leave in a couple weeks. I'm just gonna cross my fingers and hope it goes well. I did replace the ALT fuse with a new one. I haven't driven it since then but garage testing suggested no change...

[Previologist]

I've driven the Previa for the first couple of times at night since doing all of the above, and it seems much better. When I brake, the headlight dimming is still there but its minimal. I no longer feel self-conscious coming to a stop behind other cars or with oncoming traffic. Maybe the new battery helped.

The blower dims the headlights a lot more, but braking with the blower on still doesn't cause much change.

Of course my infamous blower is jury-rigged and only works on high. I might be able to reduce the drain by shortening the wires a bit, or possibly using a lighter gauge (they seem pretty heavy), but that will have to wait for another time. I'm taking it on a road trip soon and we'll see how it does.

[Previologist]

Stopped for Chinese take out tonight and when I got back in the van had inadequate power to turn over, just a faint faint faint flicker of dash lights, then dead. I turned it off completely, 10 seconds later it fired up. Three days before I leave on a long road trip. On the way home with headlights on, flipped the blower on and the van damn near shut off at 60 mph. Obviously my work is not done. The Chinese food was good though-shrimp and scallops in garlic sauce.

As mentioned previously, I've considered redoing the direct wiring from the heater relay to the blower because it seems heavier than needed. I measured the direct wire at 4.1 mm and the 4-winds aftermarket blower wiring at 2.7 mm (that includes insulation, so I couldn't calculate the exact gauge but you get the idea). Would the resistance in the larger wire potentially be causing my near-shutoff problem? It's also probably 2 feet longer than the original harness wire would have been so it is definitely additional resistance.

[tbuyan]

Larger wire (heavier gauge) will reduce resistance. Longer wire will increase resistance.

[Previologist]

Larger wire (heavier gauge) will reduce resistance. Longer wire will increase resistance.

Well this is why I hate electrics.

I guess its impossible to say then whether the jury-rigged thicker-but-longer blower wiring has more or less resistance than it should.

[tbuyan]

You can measure the resistance with an ohmmeter is you can disconnect one end. I predict zero ohms (no resistance). It would have to be a hundred feet long to have measurable resistance.

[Previologist]

Well onward I march. I found this question and answer intriguing, although it isn't Previa related.

https://www.justanswer.com/toyota/4a...an-turned.html
What you're going to find is that the air conditioning compressor has ceased or locked up. The reason why the engine stalls is because it creates a heavy load on the engine when the magnetic clutch is engaged. Whenever you're in either of the defrost modes and you turn the blower motor switch on it automatically engages the air conditioning compressor to help dehumidifier or clear the Windows.

Doing some in-garage testing, this unfortunately doesn't seem to be my problem because the headlights dim whether its on a defrost setting or not.

[man_btc]

I've looked over the thread and am not sure you measured "AC" voltage across the battery terminals with the van running (i.e. the alternator running). AC shouldn't be more than say, 0.2 volts - something very close to zero. The parts stores may have measured that, but who knows. Here's the thing - when you measure a voltage on the DC setting the display shows an average, which is only truly accurate if it's really not rapidly bouncing above and below that value. The meter on the AC setting on the other hand will only display the amount of voltage variation, which should be close to zero volts if the alternator is working properly.

If there's significant AC voltage with probes on the + and - battery terminals, that could mean while the DC voltage is staying high frequently enough to read as OK on average, it isn't staying at that voltage constantly enough to push enough steady current to everything. An AC variation might also show up as a flicker on the lights, but it might be rapid enough that your eyes perceive it as a steady, but dimmed, light. The engine computer (and thus everything it controls) could also potentially be affected by an unsteady voltage.

Presumably that voltage variation would be greater (and a bigger potential problem) as the alternator tries to increase its voltage (remember that sensing wire from the battery through fuse to the alternator? The lower that battery voltage goes, the harder the alternator works to raise it back up by increasing its voltage output to the battery. And that's certainly going to happen with increased electrical demand from brake lights and blower motors).

As a backup I suggest you make room on your dash for some garlic, wolfsbane, a St. Christopher's medal, and perhaps a small tastefully framed photo of Kiichiro Toyoda. And no stopping for Chinese food.

[Previologist]

I measured the AC across the terminals several times just now, and even read the manual on my cheapie, misnamed Smart Electrician Digital multimeter to make sure I was doing it right. I was. It came up with about 30.x volts every time, whether accessories were running or not.

I have a plastic dinosaur and fake flowers on the dash, and will only be getting Mexican carry out (and maybe some Thai) on my trip!

[man_btc]

Well, unfortunately your multimeter can't do what you're asking of it. A lot of lower-cost multimeters aren't capable of just measuring the "ripple" (alternating) voltage that goes slightly up and down around the DC voltage level (like waves on the surface of the water). That's not from reading the instructions (which I did) but from the fact that 30V AC is a nonsensically high value - the result of some "fudging" calculations that inexpensive multimeters do internally that are thrown off because the meter can't really filter out the steady part of the voltage (DC) from the changing one (AC).

Any friends who have a 'spensive multimeter with "True RMS" AC measurements you could borrow? Yeah, me neither.
Call the parts store(s) you went to and ask if they'd be willing to swear on a stack of repair guides that they actually measured the "AC ripple" when they tested your charging system?
Find someone who can?
Remove the alternator and take it to a parts store or someone who can put it on a test fixture to spin it up and make measurements under different loads.

I know I'm fixated on the alternator. If it was me, I'd want to know for certain it was working properly before I considered more wire tracing.

Also curious: Are the fake flowers for the other dinosaur who was displaced by the sudden and inevitable betrayal of the other?

[Previologist]

I called the store and they said they test for ripple but their $600 meter only mentions it if its excessive, and they didn't know what the bar was for being "excessive." Then I went and had it done again, with everything testing satisfactory.

I then priced alternators thinking maybe i would take one along just in case, but i didn't like the answer.

[man_btc]

Well, hopefully your alternator is really not, as they say, boro-boro (nearly worn out).

As agitating as it is, it'd probably be a good idea to take a deep breath at some point and start checking things from the beginning again. A visual recheck to ensure there's no obvious looseness somewhere is always good of course.

If current draw from different devices is causing a problem, the issue has to be either the voltage source or resistance that shouldn't be there along the wiring shared by all those things - meaning the battery/alternator output through the fusible links and out to the loads, or the shared ground path back to the battery from those loads (chassis and ground strap). In any kind of wire or connector, any "bad" connection is going to cause a potential voltage drop. Examples include poor contact or corrosion between surfaces, broken strands of wire, and undersized wire). Larger wires than required are not a problem; the wiring harness could be redone with jumper cables and no more current would be used.

While circuits are powered, you measure DC voltage with the black probe on battery ground and the red where you're measuring. To avoid any potential measurement problem with having the meter's circuits in parallel with what you're measuring, it's preferable to measure the voltage to ground at either end and take the difference to get the voltage change. At all points on the path to the load's "plus" input, the voltage should stay close to the battery voltage; from the load's "negative" terminal to battery negative, the voltage should be close to zero (ground). The "load" being any one or combo of things that use up voltage, not wires and switches. You may even want to consider (carefully) using pins or unbent paper clips to get into places where a multimeter probe wouldn't normally fit.

If you're measuring resistance, it should be with everything off, the probes on either side of what you're measuring, and clearly nothing else connected between those points besides what you're measuring with the meter. If you aren't positive that's the case, disconnect one end of the thing you're measuring in order to know for certain there's not also another connection between the two points somewhere else. Without that disconnect, you'd be measuring a combined resistance across multiple paths, which would be inaccurate.

[Previologist]

I wonder if I'm overlooking the obvious. We know my blower was disconnected and rewired by the previous idiot because of some problem. The harness was cut, and the cut wires are dead, the assumption being there was a problem in the harness that caused him to disconnect it. I wonder if my current problem isn't also in that same harness somewhere, which i have thus far avoided because it is hidden deep in the deepest innards of the dash-firewall and probably all wrapped up with other harnesses. Plus there was no urgent need, since the blower does work on high.

Just a departing thought, as I likely will not do much on this until I return to my garage in a couple months, unless I'm forced to.

[Previologist]

Well, hopefully your alternator is really not, as they say, boro-boro (nearly worn out).

As agitating as it is, it'd probably be a good idea to take a deep breath at some point and start checking things from the beginning again. A visual recheck to ensure there's no obvious looseness somewhere is always good of course.

If current draw from different devices is causing a problem, the issue has to be either the voltage source or resistance that shouldn't be there along the wiring shared by all those things - meaning the battery/alternator output through the fusible links and out to the loads, or the shared ground path back to the battery from those loads (chassis and ground strap). In any kind of wire or connector, any "bad" connection is going to cause a potential voltage drop. Examples include poor contact or corrosion between surfaces, broken strands of wire, and undersized wire). Larger wires than required are not a problem; the wiring harness could be redone with jumper cables and no more current would be used.

While circuits are powered, you measure DC voltage with the black probe on battery ground and the red where you're measuring. To avoid any potential measurement problem with having the meter's circuits in parallel with what you're measuring, it's preferable to measure the voltage to ground at either end and take the difference to get the voltage change. At all points on the path to the load's "plus" input, the voltage should stay close to the battery voltage; from the load's "negative" terminal to battery negative, the voltage should be close to zero (ground). The "load" being any one or combo of things that use up voltage, not wires and switches. You may even want to consider (carefully) using pins or unbent paper clips to get into places where a multimeter probe wouldn't normally fit.

If you're measuring resistance, it should be with everything off, the probes on either side of what you're measuring, and clearly nothing else connected between those points besides what you're measuring with the meter. If you aren't positive that's the case, disconnect one end of the thing you're measuring in order to know for certain there's not also another connection between the two points somewhere else. Without that disconnect, you'd be measuring a combined resistance across multiple paths, which would be inaccurate.

One of these days/weeks before I do the return trip I will do some more testing. I made it cross country, some 1800 miles, but not without incident. It only died once (while parked), but new things happened (or maybe I just didn't have opportunity to notice them in my normal driving habits close to home). The turn signal caused the radio or cruise control to turn off a couple times. The brakes seem to be dimming the headlights more again. Something reset the clock once. Gremlins I guess.