Dodgy Wiring?

[Bored?]

Trying to figure out why my tail & reversing lights are not working (mz20 soarer).

The tail light fuse blows as soon as the lights are switched on, so I assume it is a short somewhere. So I pulled a lot of wiring out in the boot to have a closer look, and I found some things that seem odd, so I'm wondering if they are the result of an evil auto electrician, or if that's just the way toyota made things.

So, here is what I am talking about: Notice how lots of wires are spliced together at strange locations in the wiring harness, and covered with what looks like blue electrical tape. I can't imagine that's factory, but I can't imagine why anyone else would have done it either. It happens in a bunch of places...
Attachment 520
Attachment 521
Attachment 522
This last one shows what's under the blue electrical tape: copper crimp connectors.
Attachment 524
Is it factory? Some retarded previous owner? Some other explanation?

Also, can anyone identify this little black box which is at the right rear of the car? I think it is some kind of relay...
Attachment 523
If anyone has any wiring info on this end of a z20, that would be really, really helpful!

[ndgcpr]

hey mate i have tried to do work on these since no one else seems to know anything about them.

My guess of that black box is maybe the sensor that tells the dash to light your light blown warning lights at night, if it is it basically measures current to the rear lights and lights the warning if the current falls below a certain amount.

Now on the wiring note, 2 things could have caused the wiring like that (although i do remember blue tape on the last z20 i worked on...

1. there has been a serious electrical problem and someone has tried to rewire it (hence why the tape is all over the place as they are "jumping" the bad spots.

2. look for anything that can give the impression that a towbar was once fitted as the plug to the trailer is usually spliced into the rear light wiring. and if so and the tow bar has been removed there should be the wires running near the underneeth of the middle of the car, maybe they are shorting.

Failing that i would go out and by alot of fuses. remove EVERY bulb and see if it still blows. if it does then its a wiring issue. if not try adding blubs and see where you can get to.

From what i can see of the pic of the metal clips they are quite common so i wouldn't worry too much about it, or maybe someone has wired something to earth cause they are silly.

Finally if the fuse does blow with no lights in try tracing wires with a multimeter and see if you can't find a culprit wire, also it could just be something broken as it passes through a hole in the metal.

[Dale]

It looks like it could be factory, for the fact they've used copper crimp joins. Being in the boot normally only one wire comes through the car to power several bulbs, ie; the parking lamps have one wire going down the body, which runs several lamps.
The other thing which makes it look factory is the colouring of the wires, with the dots and all (and all being the same). Did you unwrap it from the loom?

Check the grounds are all good, then unplug some of the lights and try them one at a time to see if it's just one in particular that's blowing the fuse

The box isn't to do with a power antenna is it? I'm not sure where they're located on z20's, but I've seen a similar box in a crown

[Bored?]

With all bulbs removed I still blow the fuse.

If I have the current measurement box plugged in but no bulbs, I get continuity between positive and ground on the tail light sockets (with all bulbs connected), but if it isn't plugged in it is open circuit. This may or may not mean something. Does the box use a resistor for current measurement or is it a hall-effect/magnetoresistive current sensor?

There are no signs of a towbar being fitted that I could see, though there is a lot of wiring going under the car (much more than required for the reversing lights in the bumper), most of it seems to go somewhere over the fuel tank. This sucks, 'cause it was a good tip.

This car doesn't have an electric antenna, the antenna is screen printed onto the rear window from what I can tell.

[BradW]

Have you just had a radio installed?

[ndgcpr]

If I have the current measurement box plugged in but no bulbs, I get continuity between positive and ground on the tail light sockets (with all bulbs connected), but if it isn't plugged in it is open circuit.

Honestly i don't know how it works but if it works much like a ammeter then the box needs to be inline for anything to, work lets see if i can't draw a pic

GND-----O-----/---------[]--------12V
GND Blub Short Box thing 12V

So remove the box and it prevents 12V going to the lights at all. I hope it made sense, let me know if it doesn't and i will draw a better (hopefully) pic in paint or something

How good are your electronic skills????

If it was me i think i would bite the bullet and rewire the thing (as in buy even more fuses and cut a wire, test if the fuse still blows, if it does, join the wire back together, then move onto the next one (heat shrink it to look pretty).

one interesting thing is that if you remove the box and the fuse doesn't blow then at least the wiring is ok to the boot.

My guess is that those wires that seem to dissapear to the fuel tank may be the culprit, but it depends how many, AT MOST i would think 3 wires to the fuel gauge sender (but probably 1 or 2) 2 wires the the fuel pump and however many wires to the bumper.

Also what exactly is blowing i don't know (and am probably to lazy atm to look) how the rear lights are wired, do you loose everything when the fuse goes? or reverse and stuff still works? and it only blows when you hit the brake or is it when the headlights turn on too?

Also roughly a blub is say 10W you have say 4 of them thats 40W at 12V.
P=VI
I = P/V
I = 3.333
V=IR^2
R^2 = V/I
R = 1.8 ohm Which means with the bulbs in you will get continuity on a multimeter...

[Bored?]

I hope it made sense, let me know if it doesn't
Not really, but that's ok. All I want to know is if "the box" contains a resistive load between +tail and ground, in which case it probably isn't the location of the short.
Well, I also would like to know which of the wires entering that box comes from the tail light fuse.

How good are your electronic skills????
Pretty good. 2 years of elec eng at uni plus some hands on experience.

If you remove the box and the fuse doesn't blow then at least the wiring is ok to the boot.
Yeah, I'm pretty sure I did that yesterday and it still blew. The wiring inside the boot tests ok, so I guess the problem is somewhere between the fuse and "the box".

Also what exactly is blowing...
The only thing blowing is the tail light fuse. The brake lights and indicators continue to work just fine. The reversing lights are not working, but this might be an unrelated problem. So the fuse only blows when you switch the headlights on.

R = 1.8 ohm Which means with the bulbs in you will get continuity on a multimeter.
Yeah, that's why I took all the bulbs out.

If anyone knows the colour codes of the wires which run from the front of the car to the boot, please let me know! You'll save me much pain and suffering.

[ndgcpr]

If you remove the box and the fuse doesn't blow then at least the wiring is ok to the boot.
Yeah, I'm pretty sure I did that yesterday and it still blew. The wiring inside the boot tests ok, so I guess the problem is somewhere between the fuse and "the box".

Well i would make sure about this, there probably isn't a need to blow fuses all the time either, just pull out the fues and if there is a short then one pin of the fues holder should read 12V with the lights on and the other should read GND weather it is switched on or not.

Again i am not totaly sure but the fuse box in the engine bay (as i am guessin this is where the fuse is that blows?) is not hard to pull apart, look underneeth the fuses and using a multimeter or something you should be able to find which wire is the one that runs to the boot. rightfully that wire shouldn't change and should be the exact same colour in the boot, (unless the fuse is before the switch or relay).

Actually do your front parkers blow also? as it may not be in the boot at all...

Your electronic skills seem pretty good so i would have a stab at fixing it, you will feel pretty good when it is all working fine

[BradW]

If you remove the box and the fuse doesn't blow then at least the wiring is ok to the boot.
Yeah, I'm pretty sure I did that yesterday and it still blew. The wiring inside the boot tests ok, so I guess the problem is somewhere between the fuse and "the box".

If the fuse still blows with the rear light monitor module disconnected then the short is further forward in the car.
Normally there is a plug for the rear wiring harness in the front kick panel. Unplug this and see if the fuse blows. If it does then the short is either in the dash lights or front park lights (as these all run off the "tail light" fuse). If the fuse doesn't blow then the short is in the wiring to the rear lights before the rear light monitor module.

Have you just had a radio installed?

It is a very common thing for people to mistakenly use the dash light wire from the factory radio as an earth when fitting a new radio (I know as I have done it myself ).
If you have had a new radio installed recently then try unplugging it and see if the fuse still blows.

Good luck with it and let us know how you go.

Edit: A tip when chasing a short is to get two short bits of wire and strip both ends. Push a piece of wire into each side of the fuse holder. Then join one strand of wire from each piece together and you have a fuse. When the strands "blow" just get another two strands and try again. When you run out of strands, cut the end off the wire, strip it back and start again. Saves blowing hundreds of fuses trying to find your short .

[Bored?]

Ok, so I unplugged the three connectors to the rear wiring harness at the fuse box in the drivers-side footwell. So I've figured out which connector has the problem wire in it, and I just need to get to the point of finding the actual wire.

Using a multimeter instead of fuses by the way, which is much cheaper

I'm thinking that rather than cutting each wire, I'll jump together individual pins on that connector until I find the right one --- saves chopping up the loom unnecessarily.

[ndgcpr]

you should be able to multimeter between the fuse holder pin and the plug on the back, it should be easy to find the right pin on the holder.

I hope that makes sense, pull out the connector, check continuity between the fuse and the pins on the back of the holder and match up with the plug. then write down the colour or post it here so you will never forget

[Bored?]

you should be able to multimeter between the fuse holder pin and the plug on the back, it should be easy to find the right pin on the holder.

Nice. I should have thought of that

[ndgcpr]

how did it go?