Please check my understanding about power back flowing via grounds (floating grounds?) and testing it (1 Viewer)

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caladin

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So in my 82 fj60, after a led Cluster upgrade, when I stand on the brake pedal, both turn signals on dash light up at about 15% brightness.(have not checked outside)

I assumed it was a bad ground on the brake light circuit feeding back through the turn signal circuit seeking a ground.

I cleaned up the a pillar grounds, no change.
So I performed a couple tests.

I found that when I press the brake the GY and GB wires into the plug behind the dash both get power.

With hazard on instead of brakes both GB and GY blink. with right turn on GY blinks, left GB blinks, verifying I have the right circuits at the plug.


Tested with brake pressed
GY on
PXL_20231001_013804565.jpg


GB on
PXL_20231001_013945158.jpg


Under the theory that this was due to a bad ground, I went to the tail lights and added a known good ground to both stop lamps.

Jump wire from the clip where the WB wire connects to back of brake light fixture. Connect to a nearby ground. Test. Both light up.

Then connect straight to the negative terminal on the battery and retest.

Both light up.

Here is my good ground setup.

Gator clip with black wire on tab with WB wire on outer stop lamp housing

Red wire to big clip is connecting straight to neg on battery
PXL_20231001_013720211.jpg


Other end of Black test lead also to same tab on right stop lamp. Theirby Connecting the grounds on both tail lights directly to neg on battery.

PXL_20231001_013614284.jpg


At this point, both are directly connected to neg on battery.

Diagram shows bo ground directly on stop switch, this is only ground in system... so connecting at lamp socket should bypass all grounds. In theory...

So if the issue is, a faulty ground, when I press the brake an neither should light up any more right?

When pressing the brake pedal, both the GY and GB still lit up.

That means I have a short somewhere right? Not a faulty ground? Did I perform the test correctly?

Since both the GB and GY wires have power when brakes pedal pressed, the short is probably on the common GW wire somewhere after the flasher relay(because it's not blinking) ?

Or it's to both the GB and GY wires?

Here are my references. If you care enough to check my work.

Closeups of parts of diagram I think are relevant, to make process easy as I can.



Wiring & harness diagram(upside down, sorry)
PXL_20231001_020126508.jpg




Close up of Brake circuit(sideway, sorry)
PXL_20231001_020137961.jpg

Close up of turn circuit
PXL_20231001_021245972.jpg


Turn signal plug pin out diagram(how I know GY and GB at plug are turn signals hot.

PXL_20231001_021224610.jpg



Thanks, any help is appreciated, I know this is a big post.

PXL_20231001_020126508.jpg


PXL_20231001_020126508.jpg
 
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If the problem occurred after swapping in LED lights in the instrument panel — remove them all and replace with normal incandescent bulbs.

If the problem goes away — then swap ONE LED bulb in and test. If everything is still good, swap in another LED bulb. Eventually you should find the culprit.
I put a LED bulb in the tachometer light and everything worked fine. That’s the only one I did.
 
Did you put in LED headlights (I did not read through everything)

If so did you use a polarity reverser in line?

I had all kinds of crazy issues on a truck that I used LED headlights, once the reverser went in all was normal.
 
Did you put in LED headlights (I did not read through everything)

If so did you use a polarity reverser in line?

I had all kinds of crazy issues on a truck that I used LED headlights, once the reverser went in all was normal.


OSS:

So the theory is a bad ground in the console circuit board? Test them one at a time to id it.

Wouldn't the fact that I can reproduce the issue at the Plug with a test light eliminate that as a possibility?

I do need to check voltage drop at the plug though, that will be useful info.

I've been researching floating grounds and the "known ground" test can be misleading, especially if you use thin gauge wire (which i did).
They said to use Voltage Drop and search all the exposed locations till you isolate the drop.

NCFJ:
I have led headlights, but they are running on their own harness that was supposed to be "Toyota ground switched friendly" , the kind that uses the power at the passenger HL plug to run Relay-led Headlights. and one of the dongles made by a mud member (Can't remember the name) to get the hi-beam dash light to work. I'm not sure what a polarity reverser is for, is that to compensate for Toyota Headlight wiring being ground switched?
 
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Toyota wiring and electric behavior can often lead to head scratching — AKA WTF?
I don’t pretend to fully understand how everything electric on the FJ60 works. Sometimes I’m at a loss too.
The issue of floating grounds is kinda mysterious on the 60 because current that’s supposed be to flow one way, finds a different path through another accessory which powers it. Dash lights illuminating when they shouldn’t is a classic example.

Sometimes when I don’t fully understand how something works, I try to devise a simple plan that can rule out possibilities just by using process of elimination.

As for your weird dash light behavior, perhaps one circuit is bad that’s spoiling the party. We may not understand how that’s happening, but if we can pinpoint what’s causing it and create a workaround (use an incandescent bulb instead of LED) the problem can be “fixed” from a usability point of view even if we don’t really know how the hell it was.
 
Got it a fix/hack.

as a programmer I'm trying really hard to actually understand what's going on and it's still kind of mysterious. It annoys me that I don't understand it exactly. So I'm trying to pin it down.

I did figure out to do a continuity test on both sides of the stop lamp to the plug and the brake switch. If I have continuity on the hot with the brake off, it's definitely a short. On ground a ground fault... So I can cut the problem in half.

If down stream of brake switch, a short on that circuit. Cutting it in thirds.

Thanks, I'll try your test and see what it teaches me.
 
Just in case this helps someone else, it was not a ground issue.

I finally tracked it down to the hacky wiring for the 4 way trailer plug.
Replaced the crimp butt spliced with spade connectors, un plugged all 4, and it went away.

Plugged the back in one at a time and it comes back when plugging left stop wire to harness.

Going to replace the 4 wire harness with a new one as the problem is between wire and plug.

Thanks for all the help.
 
Just in case this helps someone else, it was not a ground issue.

I finally tracked it down to the hacky wiring for the 4 way trailer plug.
Replaced the crimp butt spliced with spade connectors, un plugged all 4, and it went away.

Plugged the back in one at a time and it comes back when plugging left stop wire to harness.

Going to replace the 4 wire harness with a new one as the problem is between wire and plug.

Thanks for all the help.

Same on my 40; previous owner janky trailer wiring. Tore it all out and went back to stock and the problems went away and stayed away.
 
... how do I adjust float height?

Same as most any carb; take out the float and (carefully) bend the brass hinge a tiny amount at a time. There will be a spec for how far off the the edge of the carb body (minus the float bowl) it should be when hung upside down, i.e. the float needle valve is fully closed.
 
The relevant page and float spec from my 1980 factory 2F Engine Repair Manual (PDF attached). As long as you still have your stock Aisin carb, it shouldn't be too different.
 

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Thanks!
 

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