LJ78 Prado EX - electrical gremlins (1 Viewer)

[btbaker22]

Hey all. I'm a proud owner of a JDM 1991 Prado EX with the 2LTE engine. Before anyone gets on their soapbox about how the engine sucks, stop. That's not what this thread is about, and I actually like the s***ty engine in the truck. With that said...

I've been chasing an odd electrical gremlin who is causing havoc to my peacefully slow drives. The problem occurs on hot-ish days after about 15-20 minutes of driving. My peacefully slow drive is suddenly taken over by blinking dash lights (timing belt, battery, emergency, and filter), and a high pitch beep that pierces the inner depths of my soul. It is sporadic, but will continue until finally resting at it's destination. (see video)

Truck electrical upgrades: It's 12v and has aftermarket front driving lights, Kenwood touch screen head-unit with backup camera and car play. Other than that the electrical system is stock.

Things I've done to troubleshoot:
1) make a new ground for the battery (did everything your supposed to do, so I know it's good)
2) tested the battery and alternator, everything tested good even under load
3) cleaned, prodded and lubed the alternator connector with dielectric grease
4) messed with every electrical connection I could find from the top of the engine bay while the truck was running to see if I could find one that would set off the issue.

I'm beside myself with what approach I should take next. Any suggestions???

 

[Nas90tdi]

I am going to guess you are getting a charging spike of some sort. I have actually seen a similar issue. I got my alternator really wet and it was overcharging pretty dramatically for a bit. Same results less the buzzer because all of mine are unplugged.
I would start at voltage regulator. It could be failing and as it gets hot, it less effective.

 

[btbaker22]

I am going to guess you are getting a charging spike of some sort. I have actually seen a similar issue. I got my alternator really wet and it was overcharging pretty dramatically for a bit. Same results less the buzzer because all of mine are unplugged.
I would start at voltage regulator. It could be failing and as it gets hot, it less effective.

Thanks. I didn't see any spike on the battery gauge when the issue occurred. Do you think it would show there if there was a charging spike of some sort?

 

[GTSSportCoupe]

Check that your fuses are tight and making good connection. Sometimes it makes a difference just to pull them out and re-seat them. Also, you could remove your gauge cluster and re-seat the connectors in the back. It's possible someone had them apart at some point and they're loose now.

Although I think Nas90tdi is right on that there is something intermittent going on with your alternator.

And not sure if you've seen this, but here are the electrical diagrams for our trucks (translated to english by one of the members here): '90-'92 70-Series Wiring Manual.pdf

 

[btbaker22]

Check that your fuses are tight and making good connection. Sometimes it makes a difference just to pull them out and re-seat them. Also, you could remove your gauge cluster and re-seat the connectors in the back. It's possible someone had them apart at some point and they're loose now.

Although I think Nas90tdi is right on that there is something intermittent going on with your alternator.

And not sure if you've seen this, but here are the electrical diagrams for our trucks (translated to english by one of the members here): '90-'92 70-Series Wiring Manual.pdf

Thanks. Having the wiring diagram is great. Is it possible to check for intermittent charging issues if I take the alternator out, and have it fully tested? Never done that before.

 

[GTSSportCoupe]

Thanks. Having the wiring diagram is great. Is it possible to check for intermittent charging issues if I take the alternator out, and have it fully tested? Never done that before.

I would think that a competent auto electric shop could do that yet. This alternator is basically the same as other Toyota alternators of the same vintage - with the addition of the vacuum pump on the front of course (don't take that apart BTW).

If you go to the work of pulling the alternator (it's a real PITA job), just get it rebuilt and you'll have peace of mind there after.

 

[clintnz]

I have had exactly those symptoms with a loose main alternator connection. It sounds like you have checked most of that circuit now, but triple check you've covered every connection & wire between the alt & battery. Looking for voltage drop can help. Then as suggested above a faulty regulator or something else inside the unit would be the next thing that would cause it.

Rebuilding an alternator with a new regulator, brushes & bearings is not rocket science if you are mechanically minded, & you can look up how to check windings & the rectifier with a multimeter - but often an auto electrician will do it for not much more than the price of parts. With an intermittent, heat related issue they will likely replace the regulator 1st off if there is nothing else obviously wrong.

Cheers
Clint

 

[btbaker22]

Ok. I've done a big more digging, and I think the problem might be at the fusible links. Has anyone had issues with these partially failing over time? I'm thinking about removing them, and putting in an automotive breaker. Any suggestions on the size of the breaker? I believe the charge from the alternator is a separate wire that does not go through the fusible links, so I only need to consider the amperage draw from the truck and accessories I'm running.

 

[Waikato Willy]

so my fusible links just completely stopped working one day in a carpark, no power or anything with the key, if i jiggled them i could get sporadic power here and there so you might be on to something
I replaced them with a fuse box out of a nissan skyline R34

this works a treat, its got big fuses and lots of extra fuses to wire to, I just bolted it through the positive terminal clamp on the battery

Ive got a wrecked R34 skyline sitting on my property so it was easy to hack up and get this part
ignore the green arrow in the pic (not my pic) its the red circled fuses box I used

 

[manaraja]

Have you resolved this issue? the same thing is happening with my LJ78