I’ve read this 3 times and I have no idea what the power steering has to do with the alternator voltage other than they are connected by a belt.
Can you get a short belt and delete the power steering? Or is it serpentine mess?
On your electrical - voltage is good, but can you measure LOAD?
LED’s are diodes and all that old 1990’s wiring was never designed for it. You might be literally shorting something out when the load goes up?
Yes to all of the above!
They both run off the water pump. It’s belt slippage. It has to be. I’ve been thinking about this on and off since I landed.
I’m going to cut the PS belt and jump it in the parking lot. If steering inputs are affecting generator voltage, I don’t need power steering for a while.
See also, the belts aren’t even 2 years old yet. I installed all of them before the Grand Canyon trip in April 2022. The PS belt was at the deep end of the tensioner, suggesting the belt had stretched. 4 months without driving, maybe?
Ordered all new before takeoff.
Will be ordering one of these very soon, my friend. For sure. Also onboard with the LED theory. The FSM doesn’t expressly say it, but they don’t say it isn’t either.
“And at the same time”
LED bulb did not illuminate like this. I’m not very confident the incandescent does either. ONE TIME, I got it to light as I was sawing on the wheel and the volts dropped. The trans temp MIL came on at the same time. Otherwise, I’ve had no battery MIL, so I’ll be looking for it tonight when I get back to the truck.
V is meeting me at the truck. With tools. #keeper
Charge lights HAVE to be incandescent for them to work. LEDs do not have enough resistance to trigger the alt to charge. I’ve seen people try to use LEDs several times and end up with the same result, a vehicle that doesn’t charge.
@racedinanger dude! Sup!
Do you recall any of those people ever talking about how their LEDs damaged the alternator?
If I’m reading your wiring diagram correctly - Using ONLY an LED would provide the same voltage as the rest of the system, so it won’t charge - as there is no voltage differential between the ignition (load) and the alternator.
This makes sense as you arrived at your destination with a dead battery. The charging circuit never triggered.
If you smoked anything, I feel like your dash would be on fire before a coil in your alternator. 
You can check the coils by disconnecting and reading the Ohms across each. (The field coil, and the primary coil)
Back to incandescent on battery, low fuel, SRS, and AT MILs. Confirmed good.
Volts immediately came right up to 14+ and stayed there within 0.3v with high beams, full HVAC, stereo cranked, and wipers on full. Started the logger on the slow roll down the block. Lights, HVAC still on.
I’m going to have to re-cable the garage door before I can get Fezzik back inside to do more testing. Ugh.
Where is this logger connected?
Where is it grounded?
(Weird. I swear I replied to this from the email the other night.)
At this point, I’m thinking back to my electrical work while the dash was out. I don’t think I missed any grounds, because they were pretty obvious in the places I was working. See also, none of the new leads I ran for additional aux lighting are connected to anything yet.
I know my main charge cable should be replaced, but is corrosion really going to behave like this?
Drove the truck to the other side of town over the weekend to pick up a piece of used furniture. Voltmeter stayed in the green the whole time. Even with the radio going. It was slowly–slowly–dropping, but it’s like, when it’s working, it’s working fine, which means the issue is something related to signal.
In the meantime, I’ve got the garage door to an acceptable level of disrepair such that I can open and close it and pull the truck back in for work, but now there’s a piece of used furniture in there needing sanded and painted.
(Getting V into the garage > getting Fezzik on the road these days.) 
V’s got a thing up in Cedar Rapids tonight, so I’ll have a few hours to myself.
At this point, I’m thinking loose connection somewhere. I’ve driven the truck five times in the last week. Each time, it started on the first try and the volts came right up to 14 within a few seconds of the starter disengaging. The big voltage drops don’t correlate to any amount of accessory loading.
Voltage readings at the gauge (12V outlet) pretty much match what the PCM is seeing via the logger. When they’re low, they’re legit low, as evidenced by visibly slower wipers and audibly slower HVAC fan, but activating these accessories makes little to no impact on the gauges in these situations.
So far, only the brake pedal seems to have any potential cause/effect on things. I doubt it’s my LED tail/brake lights (that have been there for over two years now). Combined with the gauge randomly dropping while I was just driving along a less-than-smooth county road yesterday and staying there, it feels like something is loose or not connected and said connection is affected by G-forces in motion.
Fucking physics. Back to the lab!
Thoughts/advice?
I just realized the scale on the logger for the first time. I thought that was dropping down to 8 - 9v. Now I see is was always more than 11. Yeah, the car won’t start, but the ECU etc will still compute. I assume the voltage AT the battery is the same?
I agree that something may be loose and randomly under braking it gets disconnected / shorted.
With the logger in hand / phone and truck running - grab the power charging harness and pull on it.
Check the grounds of that harness. What does the engine ground look like?
Do you have a spare connector for the alternator kicking around? Maybe we should build our own charging circuit and take it away from the hands of the PCM.
Good Luck!
Back to the drawing board, I guess.
Ran out of time last night, as V was supposed to be in Cedar Rapids assisting with a theater production until around 1030pm–but nobody told her the show was canceled, so she drove 45 minutes to a dark, empty building and back. We got to talking. Time flies.
Pulled the intake so I could inspect the full length of the charging harness between the firewall and alternator. It’s intact, but looks shitty enough that I’m just going to go ahead and run new leads, starting with a new, 4AWG OGF cable up and over the top of the engine to the battery.
Behold! My embarrassingly fugly physical layer!
I pull-tested the following:
Started right up like nothing was wrong after all this, but I haven’t driven it yet to see if I’m going to get away with pure, straight, dumb luck on this front. 
Appreciate not being left to my own devices on this one.
Long story short: Dirty IAC was sticking, and not compensating for loads. The other night while I was testing the harness, I noticed the revs dropping to 300rpm when I blipped the throttle.
This afternoon, I cleaned the TB and IAC out real good with carb cleaner. Used a rag on the IAC, as I read some stories about how spraying them kills them. Buttoned it back up and I’ll be damned if I can get it to drop below 14.1v now.
Didn’t have time for a test drive, but that will come soon.
I’m not saying you didn’t have a problem with the IAC.
I’m also not saying that you had just one problem here.
– but 300 RPM’s the difference between charging the battery and discharging it?? 
hmm.
– Kris
I know what you are saying. And I agree. It don’t quite add up.
– but what if it’s not that we’re seeing discharge so much as charging voltage on the meters?
As I understand it, alternator output (potential) correlates to RPM, and the “110A” Denso alternator on my truck likely needs to turn at minimum speed in order to deliver all those amps. Between loose belts and a sketchy IAC, I think it’s possible the issue was caused by the engine not being able to idle back up to where the alternator could meet those minimums.
Man. I sure hope that’s what it was.
Under braking, makes sense that the sticking IAC wasn’t recovering. Especially with the vacuum assist for braking. Revs dip below idle. Voltage drops on its head. Okay - well - let’s hope so.
Exactly.
See also: Next problem on my list is vanishing brake fluid. Already somewhat isolated to FR UCA location. Fluid level sensor wire is missing from master, too. But hey, I know the booster is still good.
New OEM Door Seals!
Crawled under Fez to look for signs of a leaking brake line. Only leak I found appeared to be tcase or transmission, so I decided to chase some easy wins for a while.
NIB, direct from the UAE.
Can’t wait to test drive later tonight!
E: Test drive success. Got my win. It’s still obviously a 26-year old, body-on-frame truck–but you can hear a whisper in the front seats now.
Somebody made it to DSM and back without any issues yesterday. 250ish miles round trip. Two hours each way, with lights and heater running, radio cranked. 13.9V all day.
Wo0t!
Haven’t seen any brake fluid leaks or loss, either. Which is weird. Something tells me I’m going to end up replacing the booster and master cylinder this summer on principle.
Both are OE and 28 years/260kmi old. The low fluid level sensor wire came out of the side of the master and doesn’t appear to go back, so it’s either that or pull the MIL bulb in the cluster.
If I’m pulling the master, might as well replace the booster too, right? Right?
