Rear lights, speakers, and locks not working after rain & brake job

[cr0nis]

Hi folks,
I’m hoping someone can help me troubleshoot an issue with my 1991 Previa.
I recently had the front brakes changed, and on the drive back home, I noticed that the rear lights, some interior lights, front speakers, and a few other electrical components suddenly stopped working.
I heard this could be related to a shared fuse, so I checked the TAIL fuse—it looked fine, but I swapped it out just in case. Unfortunately, that didn’t fix the problem. Headlights are still working, but the power door locks and other affected systems aren’t responding.
Digging deeper, I removed one of the rear brake light assemblies and found water on the wiring—likely from last night’s rain. Coincidentally, it also rained the night I drove it home after the brake job. That side also happens to have significant rust in the wheel well, so I’m wondering if there’s some kind of short or corrosion-related issue.
Could this water exposure be the culprit? Or is there something else I should be checking before I go too deep down the rabbit hole?
Appreciate any insight—thanks in advance!
Cheers,

[Previologist]

I don't remember the exact details because my 91 passed away 18 years ago, (I think it was my 91 but my memory passed away around then too) but I do recall having multiple inexplicable and seemingly unrelated electrical problems (that, like yours, did not include headlights) that I traced to a rear light problem of some sort (thanks to Grumpy Old Fred on the Yahoo list). Maybe Dan can even find it in his archive if he's inclined to look. Barring that I would just recommend checking every single lighting wire and socket and bulb in the back of the van. To start.

[John Kaufmann]

... 1991 Previa.
I recently had the front brakes changed, and on the drive back home, I noticed that the rear lights, some interior lights, front speakers, and a few other electrical components suddenly stopped working. ... Headlights are still working, but the power door locks and other affected systems aren’t responding.
Digging deeper, I removed one of the rear brake light assemblies and found water on the wiring—likely from last night’s rain. Coincidentally, it also rained the night I drove it home after the brake job. That side also happens to have significant rust in the wheel well, so I’m wondering if there’s some kind of short or corrosion-related issue.
Could this water exposure be the culprit? ...

It's likely that water and/or corrosion are at least part of the problem, so I'm attaching the power and ground pages from the 91 Previa EWD:

Pages-(Chapter) TOPIC	SHOWING
022027-( 9) Wire_Routing-Connectors_Grounds_Splices.pdf	Locations of Connectors, Grounds and Splices on the van
028037-(10) Power_source_flowchart.pdf	Power/fuse branching
040042-(11) Power_source.pdf	Fuses
150153-(44) Ground_points.pdf	Ground points branching

For example, ground point BF is over the Rear LH wheel well, BG over the Rear RH wheel well.
From what you say, affected components are: rear lights, power doors, front speakers and some interior lights.
You should be able to check exactly what is working/not-working against the power and ground branching diagrams.

[cr0nis]

These are amazing. thank you so much. I'm printing them up now and working through it.

On a side note, do you know where I would be able to but the EWD, Repair Manual and the Transmission Manual in PDF? I'm planning on keeping her around for a bit and am looking at hard copies which are fairly pricy these days.

Thanks

Leo

[man_btc]

do you know where I would be able to but the EWD, Repair Manual and the Transmission Manual in PDF?

If no one has that info and shares it with you, there's always https://techinfo.toyota.com, which -at least the last time I used it - you can subscribe to for even a couple of days at a reasonable price, at which point you poke around and download like there's no tomorrow before your couple-of-days subscription ends.

And as a side note, back on the original topic, and with apologies in advance because I don't know your level of electrical knowledge - if you don't find something obvious, things will go a lot better if you're measuring (voltage and resistance) wiring and connectors rather than just looking at them and unplugging/replacing/wiggling. Knowing some basics about voltage, current and resistance is hugely helpful. Any relatively inexpensive multimeter is OK for that; one that costs a bit more but automatically goes to the correct measurement settings, like the "Southwire 16030A Autoselecting CAT IV Multimeter" can be more convenient.

[John Kaufmann]

... do you know where I would be able to but the EWD, Repair Manual and the Transmission Manual in PDF? I'm planning on keeping her around for a bit and am looking at hard copies which are fairly pricy these days.

As Dan said, I got them from TIS, when we were keeping our Previa for 31 years and ~320K miles. (I also had the paper FSM.) During that time the Previa forum at Yahoo Groups was a great resource, and I uploaded the EWD and FSM to their library. (Someone else uploaded the 96 FSM, so we had both generations on file.)

When Yahoo Groups shut down, that library disappeared with it. No particular reason not to do the same again, but this forum does not have comparable resources, and I just have not thought about an alternative.

[cr0nis]

The files and link pointing me to TIS was enough for me to also find charm.li. Was able to find a decent resource there as well and took an offline version of it. I'll probably still get a hard copy since it just seems easier, but charm.li seems to have a vast amount of information as well.

I'll report back on my findings once i can get under the car this weekend.

Cheers

[John Kaufmann]

The files and link pointing me to TIS was enough for me to also find charm.li. ...

Very nice!