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<--- Scott, oh...
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Discussion Starter #1
Cliff Notes:
1) Battery unplugged + No key in the ignition
2) Battery plugged in + No key = headlights pop up & turn on w/CEL

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My '86 MR2 developed the well documented issue with the interior blue junction box (#3?) - both turn signals were lit solid when turning on the headlights, the engine rpm would drop, the electrical meter would drop. So my dad and I set out to fix it this weekend. We were able to remove the box, remove the poorly soldered pin and replace it with our own wire.

We put everything back together, connected the battery and the lights popped up and came on... which was great, but the key in the ignition wasn't turned on and the headlight switch was in the "off" position. In addition to that, the check engine light was on... while the key wasn't in the ignition.

Continuity was checked on the headlight switch, the two relays in the frunk and the ignition. All looked good. Disconnected the battery, took everything apart, put it back together, same issue... Took it all apart again and started to test continuity on the junction box. I think our next step is looking at individual connections to make sure they are right. This thread is going to be helpful: http://www.mr2oc.com/showthread.php?t=455914

Anybody ever seen anything like this? I'm not very optimistic about tracing wires. Part of me wants to just buy a new interior harness. I have a spare headlight switch, but the behavior was the same without the switch plugged in. The only time the CEL turned off was when the headlight relay was removed.

I may at least find a second harness on the off chance that I end up "fixing" the car worse than it is already :p

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I would start with the CEL. Either the ECU is getting power without the ignition, or the CEL wire is shorted. Those are both relatively easy to trace, and the cause may lead you to the rest of the trouble.
 

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Wow that pin was really getting hot.
You say this is a well documented issue? Have others had problems in the past with that junction box?
Do you know what circuit was on the pin that was getting hot?
I would think that in order for it to get that hot something down stream would have to be drawing an excessive amount of current.
That or the connection was very poor.

I had an electrical scare of my own recently while rebuilding my DD FX16.
I turned my key to on at one point and nothing worked but the fuel pump would kick on for no reason, then my gauge cluster would no work unless I turned on the over head light OR the Ebrake. Then my coolant gauge started spiking when turning key to on, then it started smoking from the gauge cluster.
I was freaking out. All I did was try to charge the battery because it was acting as though it was dead. I charged it while connected to the car too. I guess it over charged it or shorted it out internally or something because after that is when ____ got crazy.
I measured 17+ volts with my meter at the battery terminals.
I removed my gauge cluster to check for "smoke damage" and found that the Ground trace on the cluster's plastic circuit mat had gotten very hot but not broken thankfully. After I got a new battery everything was fine, It was the strangest thing I have ever seen.

I know this is super long winded and has really nothing to do with your post but I do feel your pain.
 

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<--- Scott, oh...
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Discussion Starter #4
I would start with the CEL. Either the ECU is getting power without the ignition, or the CEL wire is shorted. Those are both relatively easy to trace, and the cause may lead you to the rest of the trouble.
Yeah, something has to be crossed. I'll give tracing the CEL specifically a shot. Right now we've been trying to verify the junction box is wired up properly. If it's not, we're planning on removing some of the connections from it and hooking them up outside the box.

Wow that pin was really getting hot.
You say this is a well documented issue? Have others had problems in the past with that junction box?
There are various threads regarding the blue box near the driver side kick panel. I followed the instructions to fix it from here:

http://www.mr2oc.com/showpost.php?p=4458424&postcount=8

It seems like the heat from the wire did enough damage to foul up another circuit.

Do you know what circuit was on the pin that was getting hot?
I would think that in order for it to get that hot something down stream would have to be drawing an excessive amount of current.
That or the connection was very poor.
So far my dad and I have cleaned up a lot of the grounds. It's amazing how much paint there is around them and how little "metal to metal" contact is going on.

We also tested the relays using the methods from the BGB. Everything looked ok... I even removed the headlight switch from the car, plugged in the battery and it the same thing happened, lights up and on immediately.

I'm considering replacing some relays anyway, but it's a longshot. Otherwise it's back to reading electrical diagrams and tickling connections with the multimeter.

I had an electrical scare of my own recently while rebuilding my DD FX16.
I turned my key to on at one point and nothing worked but the fuel pump would kick on for no reason, then my gauge cluster would no work unless I turned on the over head light OR the Ebrake. Then my coolant gauge started spiking when turning key to on, then it started smoking from the gauge cluster.
I was freaking out. All I did was try to charge the battery because it was acting as though it was dead. I charged it while connected to the car too. I guess it over charged it or shorted it out internally or something because after that is when ____ got crazy.
I measured 17+ volts with my meter at the battery terminals.
I removed my gauge cluster to check for "smoke damage" and found that the Ground trace on the cluster's plastic circuit mat had gotten very hot but broken thankfully. After I got a new battery everything was fine, It was the strangest thing I have ever seen.

I know this is super long winded and has really nothing to do with your post but I do feel your pain.
That is really strange - glad you got it fixed. I may end up removing the cluster to test it out, inspect it and see which wires go to it.
 

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<--- Scott, oh...
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Discussion Starter #5 (Edited)
We just tested the Headlamp Retainer using the BGB prescribed method and it failed... would a bad one cause this issue?

Part # 89561-17010
Located Frunk, Driver Side

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http://www.mr2oc.com/showpost.php?p=2662281&postcount=16

Martin noticed this thread and suggested that I pass on some info about a feature that came with some of our MR2's called the Light Retainer Relay.

The Light Retainer Relay came stock with the 85 and 86 MR2's, but was "missing" in some of the 87 - 89 models. It is located in the frunk mounted on the "firewall" in the corner just above and to the right of the clutch and brake master cylinders. The part number of this relay is 85961-17010 and is not to be confused with the Retractor Control Relay that controls your headlight motors.



The Light Retainer Relay relay prevents you from ever running your battery dead by automatically turning off your headlights when you leave the car. An added benefit is that it saves wear and tear on your headlight switch for those evening runs to the 7-Eleven or the gas station.

I found out that some of the Gen 1 MR2's did not come with this relay. Instead tucked behind the brake master cylinder was the wire that should have plugged into the relay. For those models, Toyota installed a jumper connector at the end of the cable instead of the relay. The good news is, if you remove the jumper connector, you can install the relay "plug and play". The mounting hole is already provided for you and no wiring is required.

How the relay works: The relay gets a signal from the driver's side courtesy light switch (the switch that turns on your dome light when you open the door). If you leave your headlights on and shut off your engine, when you open the door, your headlights will turn off automatically. You can reset the relay (and turn your headlights back on) by either turning your headlight switch to the off position, then turn it back on, or by restarting the car.

After seeing so many people run their batteries low by leaving their aftermarket fog lamps on, I ran a second Light Retainer Relay to control the fog lamps. I highly recommend getting one if you don't have it.



http://www.mr2oc.com/showpost.php?p=4253440&postcount=7

Fuses are separate for left and right, so not the fuses. If the high beams work correctly in the flash mode, but not in the normal mode, I would guess that it is the main switch. The second guess is the headlight retainer relay that does the control logic for the lights and motors.
 

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<--- Scott, oh...
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Discussion Starter #7
Depends on how bad it is. Just try pulling it and see if things get better.
It failed at (c), there was voltage between 8 and 2 & between 1 and 3 after the ground was attached to terminal 6:





I'll put things back together this evening and see how removing that relay affects what's been happening.
 

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<--- Scott, oh...
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Discussion Starter #8 (Edited)
Without the retainer relay, the lights would still pop up as soon as the battery was plugged in and then go down when the key went beyond "lock". The CEL was no longer lit though...

Removing the retractor relay prevented the headlights from going up automatically and it did some funky stuff when we ran the continuity tests on it while connected to the battery(sparks).

Now with the retainer and retractor relays removed the lights stay down, there's no CEL... but the tach, oil and coolant gauges aren't working. Does this sound right?

Replacement relays en route - looking at wiring diagrams.

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Looking at the 7.5A fuse...
 

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Now with the retainer and retractor relays removed the lights stay down, there's no CEL... but the tach, oil and coolant gauges aren't working. Does this sound right?
Not right, but now you can trace power to the gauge cluster. That circuit is completely unrelated to the headlights.
 

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<--- Scott, oh...
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Discussion Starter #10
Not right, but now you can trace power to the gauge cluster. That circuit is completely unrelated to the headlights.
What's weird is that the coolant temp gauge worked before I soldered the wire to junction box #3:

I replaced the 7.5A "Turn Gag" fuse, still no tach.

  • Parking Brake Light works
  • Turn Signals & Hazards Lights work
  • Voltmeter Works
It does look like the signal from the igniter, oil pressure sender and water temp sender travel across the ribbon wire from JB #4 to JB #3... maybe my issue is still there.



I'll check the connection behind the driver seat:
http://www.mr2oc.com/showthread.php?t=401379

I'll try to trace more wires this weekend, but I'm getting the feeling that I may just need to replace juction box 3 & 4 or the entire harness :
http://www.mr2oc.com/showthread.php?t=258026
http://www.mr2oc.com/showthread.php?t=344203
 

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Can you identify the wire colors associated with the smaller burnt white connector in your first post? I'm good with the elect BGB and might help with causation?

The burnt section of the dreaded #3 Junction Box you showed in your first post (at the bottom) appears to be the 3E section specifically the #5 and #6 terminals. (Page 16 Electrical Service Manual)

Believe it or not this is the defroster switch circuit to ground. These defroster circuits carry large current loads to do their job BTW. This circuit is controlled by the 20A defog fuse which may or may not have blown prior to this scorching issue as the wires in this stupid assed #3 Junction Box are quite small and may have fried before tripping the fuse.
(Page 87 Elect Serv Manual)

Mister 2 Tim
26 year owner
SC ToyZ RacZing
 

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<--- Scott, oh...
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Discussion Starter #12 (Edited)
Can you identify the wire colors associated with the smaller burnt white connector in your first post? I'm good with the elect BGB and might help with causation?
White-Black | I'm pretty sure it's E6:



The burnt section of the dreaded #3 Junction Box you showed in your first post (at the bottom) appears to be the 3E section specifically the #5 and #6 terminals. (Page 16 Electrical Service Manual)

Believe it or not this is the defroster switch circuit to ground. These defroster circuits carry large current loads to do their job BTW. This circuit is controlled by the 20A defog fuse which may or may not have blown prior to this scorching issue as the wires in this stupid assed #3 Junction Box are quite small and may have fried before tripping the fuse.
(Page 87 Elect Serv Manual)

Mister 2 Tim
26 year owner
SC ToyZ RacZing
E5 looks like it may have some affect on the clock. That's working at the moment.

I'll admit that I'm an electrical wiring newbie, so any help is appreciated :thumbup

I'll double check the fuses.

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Replaced a few more fuses that looked somewhat related, no change.

Headlight Retainer and Retractor relays should arrive tomorrow, but I'm not expecting them to solve my instrument cluster issues.

I received some advice to check the rear trunk wiring connector beneath the ECU for burnt or corroded pins. Another guy told me to trace all the problems starting from the ECU... and I'll try to check if there's voltage at the instrument cluster for the oil pressure, coolant temp and tach gauges.
 

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<--- Scott, oh...
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Discussion Starter #13 (Edited)
Interior to engine harness connection:





^ The small wire was stuck to the bottom of the car. You can see the black line from the insulation.

So I'll be cleaning up my grounds this weekend.
 

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<--- Scott, oh...
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Discussion Starter #14
So I started inspecting the grounds in the engine bay, removing a lil' paint, sanding and applying dielectric grease. My negative battery cable looked like it had been roasting a lil' and the nearby connector wasn't keeping connections together:



I spent some quality time with my dad and a voltmeter testing connectivity between JB #3 and JB #4. Everything came across, but we were getting weird readings on the board. Single pins on JB3 connector F were all over the place and were connected to multiple pins on the ribbon cable...



so I'm thinking that JB #3 is where the problem lies. I'm trying to source a new one for my particular model/options. Supposedly the part number label on JB#3 helps:



This really sucks. My MR2 was running really well and I had just fixed the last minor oil leak it had *sigh*...

In the meantime I found a 1987 FX16 GTS to drive around. No electrical problems, but bad oil leaks.
 

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I have a full body harness from an 89 SC in my parts if it helps.
I did remove the circuits for the sc light and R/P switch from the dash harness to add on to my 86 when I put a gze in it.
I saved all the wiring from the doner car including that panel, let me know if there is anything you might want.
 

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<--- Scott, oh...
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Discussion Starter #16 (Edited)
I have a full body harness from an 89 SC in my parts if it helps.
I did remove the circuits for the sc light and R/P switch from the dash harness to add on to my 86 when I put a gze in it.
I saved all the wiring from the doner car including that panel, let me know if there is anything you might want.
Thanks! I think the junction boxes are different based on years(85-86 vs 87+) and options(Cruise Control, Auto/5spd), but I'll look into if it would be compatible.

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New(used) compatible harness en route.

I was also looking into if anyone locally could reproduce the board. Living in Silicon Valley should make it easy to find someone, right?
 

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<--- Scott, oh...
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Discussion Starter #17
Headlight relays - $20
Wiring harness - $80
Meantime beater car - $2000
Discovering that you connected the ribbon cable the wrong way after 4 weekends of tracing wires and taking apart the interior - Priceless
 

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I wish I would've seen this thread earlier, when my box did this I made the same mistake as you did.

When something is screwed up after you mess with something, I always use the logic of, what did I screw with last and start there. But at least you have an Fx16 from this encounter, those are still harder to find cars.
 
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