Wiring Harness Shorting Issue.

[Howitzer]

Hey all. I try not to post too many threads asking for advice, and just figure it out on my own, but I am stuck, stumped, and would like your guy's help before I snap my crayons. Problem is in my 87 4runner, 22re, w56.


So, I believe I have a short in my wiring harness, somewhere in the tail light/marker light/ gauge cluster light etc circuit. I have been dealing with this problem for about two years now, and have tried multiple times to solve it, tonight being one of them, to no solution. I've ended up screwing red 12v trailer lights into my rear bumper and running to a toggle switch and using a LED glowstick for my gauge cluster, which has lasted me these two years.

At first, every time I turned my lights on, it would blow the fuse. Then, last time I tried to solve the problem, the fuse has stopped blowing. I have checked the wires in the harness (as per the crummy wiring diagrams I have, which don;t really help much), and don't see any visible shorts or exposed wires or cuts or arcing or anything. I haven't torn up the dash to look behind the gauge cluster, but I doubt it would be there. I checked continuity in the marker lights in the front end, and they're all tone out alright. I wish the fuse would blow again so I can isolate different areas of the circuit to see which area it's in, but it won;t even blow anymore. Incomplete circuit? The wiring diagrams I have are shiesty, at best, and don't really help much besides vaguely tell me what is included in the circuit (what all is included in the circuit?). I've tried to do some research on it, but can only find what I already "know" about it. Please help, guys. I'm losing a lot of energy and soul, I love this truck to bits, and want to SAS/7mge swap it, but am really hesitant to if I can't fix this.

Thank you all for your time,

Engel

 

[KidVermicious]

I've got $5 on aftermarket wiring. I'd concentrate your search on everywhere it might have been tampered with - scotchlocks on the taillight wiring for trailer lights are a prime culprit, so look behind the access panels in the bed. Also look for crap stereo wiring - the stereo illum circuit is on the same fuse as the gauge cluster and taillights (ask me how I know ).

Check the stickies up top for a link to download the factory service manual, which contains unsheisty wiring diagrams.

 

[Howitzer]

Pardon my un-knowledge, but scotchlocks are those incredibly stupid plastic tab things that (should never have been invented but were) clamps over a wire to steal power from it to go to another wire? I installed the stereo myself, so I really hope that's not the issue *insert embarrassed face here* What do you mean by the stereo illum circuit? I understand that it's on the same circuit as the tail lights and gauge cluster, and forgive the stupid question, but wouldn't the stereo not light up/function if they were grounding? Thank you for replying, KidVermicious, I appreciate your help!

 

[KidVermicious]

Yup, that's a scotchlock.

Every stereo I've installed has had three 12v sources into the back of the unit - power (switched 12v), memory (constant 12v), and the illum wire, which switches with your headlights. Or tail lights, to be more accurate. The stereo will still function without the illum, but the backlight won't work. Although maybe if you have an LCD display or some such you don't use the illum wire? I dunno. Anyway, if that illum wire is loose and shorting out to ground that could be the cause of the fuse blowing.

 

[Howitzer]

I don't know why anyone would ever have invented those stupid things. Lets just cut into a wire, destroying it's oxygen barrier and not to mention actually cutting into the wire. That's just my views on it.

My drivers rear taillight has a couple scotchlocks on it (one of the couple times I've tried to fix this I removed the hack trailer controller and the wiring, and just trimmed the wire off the scotchlock and wrapped it in tape to insulate it to prevent grounding), so I will cut those out and solder in a replacement chunk. Could a corroded scotchlock be a plausible reason as to why the fuse wont even blow anymore, ie the circuit wont complete?

And It is an LCD deck, I believe, but I will pop it out and check the wiring behind it!

I don't have a garage (that has anymore room in it, as the 67 chevy is under resto), so I will call around and try to pull a favour, or else go into the heated mall underground parking. hehehe

Also, I tried to download a FSM, but I missed my opportuity and the link is down (for the first generation trucks, at least). I tried toggling back a couple years (what another member said he did on that site) and the first generation fsm is still unavailable. Is that the only online source for it? I don't really want to be a bother and ask someone on here if I can mail them a USB stick, but desperate times calls for desperate measures

 

[Howitzer]

KidV,

It's not the scotchlocks, but they were in the drivers rear compartment of the tail light assembly. I tested continuity on all three, and they all toned out fine, I did however cut out the scotch locks and solder the wires back together (I can provide pictures later if I can figure out how to get them off my iPhone). And there are also no bare wires or anything of the sort behind the cd deck. I could not find a illum wire specifically, but I did look up and down all the wires and there are no shorts or cuts, etc.

Any other ideas?

 

[brifri01]

when a fuse blows its a short from positive to ground. A wire with corroded scotchlock creates high resistance.
Is the headlamp switch with parking lamps only what did blow the fuse?
or is it the headlamps?

the best way to check the circuit is do the wiggle test. Turn the switch on and wiggle all the wiring starting at the steering column ending at the socket.

check the sockets all of them. do they all illuminate on your switch?

 

[Howitzer]

when a fuse blows its a short from positive to ground. A wire with corroded scotchlock creates high resistance.
Is the headlamp switch with parking lamps only what did blow the fuse?
or is it the headlamps?

the best way to check the circuit is do the wiggle test. Turn the switch on and wiggle all the wiring starting at the steering column ending at the socket.

check the sockets all of them. do they all illuminate on your switch?

After I tore the scotch locks out of the tail light, and soldered it back together, it still wouldn't work. It's gone from blowing the fuse, to not even popping the fuse anymore. I can't get a fsm at all, thus having shiesty wiring diagrams, haynes manual is of little help, I'm literally going insane! None of the scotch locks looked corroded, but I replaced them anyways.
Yes, it was the headlamp switch that "caused" the problem, whenever I switched it on, it would blow the fuse, and the gauge cluster didn't light up/tail and marker lights didn't come on, but the headlight and signal light functions on that switch worked fine. Now, however, it won't even pop the fuse, marker/tail light an gauge cluster lights dont work, and the headlight/signal light functions work just fine. UGH!! My compound bow is staring at me in the corner of the garage, I tried to threaten the 4runner but she wouldn't listen to reason

 

[KidVermicious]

Now, however, it won't even pop the fuse,

I'm out of ideas, but if it's not popping the fuse, are you sure it's even getting that far? Maybe it's the switch, do you have a multimeter?

I don't know how to read a wiring diagram, but do these help?

 

[helo-mech]

I can't get a fsm at all, thus having shiesty wiring diagrams, haynes manual is of little help, I'm literally going insane! :

Send me your email address regarding the FSM.

Also, now that you are not blowing fuses, take a look at your connections behind the tail lights. If I remember correctly there are some grounds that run to the support posts on both sides. One of mine came loose once and it created all kinds of havoc with my gauge lights and tail lights. It got to the point were my gauge would light up when I pushed the brakes. Then it would swap and light up my front running lights regardless of what position the headlamp switch was in.

I hate wiring woes. THEY ARE A PITA!!!!!!!

 

[helo-mech]

've ended up screwing red 12v trailer lights into my rear bumper and running to a toggle switch and using a LED glowstick for my gauge cluster, which has lasted me these two years.

Engel

I have to say though, that is some ingenious work around. I respect the hell out of these types of "fixes." That is what people used to do back when we weren't a "throw it away" society. I remember working with my Grandfather and a repair or fix didn't have to look pretty. It did however have to function and keep us from having to go pay someone else money that wasn't available to make it look perfect.

I still remember having to close a gate latch on the dryer at my house. From the time I learned how to help out with the laundry to the time I moved out, if you forgot to close the gate, the door would open in the middle of the run and your clothes would still be wet when you woke up. Before the latch, there was a stick we wedged between the wall and door.

 

[Howitzer]

I'm out of ideas, but if it's not popping the fuse, are you sure it's even getting that far? Maybe it's the switch, do you have a multimeter?

I don't know how to read a wiring diagram, but do these help?

View attachment 106139

View attachment 106140

These are a little more clear than what I have; thank you!! I do have a multimeter, and tore apart my dash a little bit, and the switch is working perfect. Tail light relay, perhaps? Although, the only relay I have ever had malfunction on my was a circuit opening relay on my 91 pickup and that's only due to water dripping down the inside of the A-pillar due to rust and dripping onto it. I have the part number for the relay, but no idea what is the protocol for testing it. I used to be "friends" with a single mom who worked in parts at a toya dealer and got me crazy deals on prices and advice from their mechanics, but she no longer works there so my resources are dry Just a though, if I disconnect the body harness that separates the front/rear half (situated right below the drivers kick panel and fuse panel), would it completely break the circuit and render it inoperative, or would it just isolate the rear half of the circuit from the front half? That way I could tell if the "break" in the circuit is in the front or rear half of the truck and narrow it down. Problem is I don't even know what all is on the circuit to even look for, it seems every wiring diagram tells me different things are on it. Almost ready just to physically run wires to all the marker lights and guage cluster and wire it up to a toggle! however, that would be a PITA and I refuse to give up. I also checked the gauge dimmer switch (rheostat?), and it is operational.

 

[Howitzer]

Send me your email address regarding the FSM.

Also, now that you are not blowing fuses, take a look at your connections behind the tail lights. If I remember correctly there are some grounds that run to the support posts on both sides. One of mine came loose once and it created all kinds of havoc with my gauge lights and tail lights. It got to the point were my gauge would light up when I pushed the brakes. Then it would swap and light up my front running lights regardless of what position the headlamp switch was in.

I hate wiring woes. THEY ARE A PITA!!!!!!!

PM about to be sent, THANK YOU!!!! I looked and cannot see any grounds that run behind any of the tail lights, although a crummy ground ((somewhere)) does sound like a new idea I have not tried yet. The drivers rear light assembly had some scotchlocks in there from the previous owner (if I ever get my hands on him, the amount of stupid useless sack of monkey feces wiring he did all through the truck is insane, so I am not surprised this has been such a PITA to figure out), but it was on the signal/brake/backup circuit, and continuity was fine on all of them, but I solder-replaced them all out with regular good ole wire)

In regards to your respect for my ghetto fix; thank you! Its absolutely hideous, but, it ensures a safe driving condition for myself and others on the road, and keeps the tickets away. I appreciate that, and I appreciate your words about your story with your grandfather. I cannot stand todays throwaway society. Fix what you have, maintain what you have, and appreciate what you have.

 

[crash813]

Definitely feel for ya. I spent hrs and hrs pulling out an early '90s alarm system that was already semi-removed. It was a cluster.

As you probably already know, the biggest kicker is the illumination circuit as that goes just about everywhere: radio, dash lights, switches, etc. Hard to isolate and track down.

If you were blowing fuses before and now its no longer blowing fuses but still no power then something else ate itself in the path. Probably a relay. Hopefully, you were putting the right amp rating fuse in each time. Even then, a spike higher than the amp rating can go down the wire before the fuse pops.

What I would probably do is visual checks first:
- trailer wiring, always crappy connections and i've seen more than a few fall loose and short out on the exhaust pipe.
- radio/cig lighter, see above, crappy connections, too many borrowed powers, etc
- front marker lights, esp if someone added fogs, bumper, etc. Improperly ran wires can easily fray on sheetmetal.
- check around the rear cargo light, my PO did a lot of hokey pokey with those wires running power to various things in the cargo area.

If nothing stands out, then start running continuity tests at different harness connections between power and ground. Basically looking for the short. You don't need power for any of these tests. Find the short first, then find out the reason for no power, ie. the relay or whatever else.

Another useful concept to understand is the floating ground concept that the interior lights use. 4crawler has a pretty good write up here when talking about upgrading headlights. Read the paragraph about Implications of Switched Ground.

Toyota 4Runner and Pickup: Brighter Head Lights

Hope some of this is useful to you. If still no luck, you might try reaching out to 4crawler as he is (i belive) also an electrical engineer and is very helpful. He's usually on yotatech.

 

[helo-mech]

88 FSM https://www.dropbox.com/s/dhgarkhctj5ffec/88 4Runner and Truck.pdf

Should not be any difference from the 87.

 

[helo-mech]

88 Wiring Manual https://www.dropbox.com/s/zrf607w1j7v4jqn/88 4Runner Wiring.pdf

Excerpt for Taillight and Illumination:

 

[2ndgen5vze]

I have had something like this happen to me before . Check the rear tail light bulbs remove them and see if that helps. Those older bulbs get corroded and short out when they turn on. Just a thought.

 

[KidVermicious]

88 Wiring Manual https://www.dropbox.com/s/zrf607w1j7v4jqn/88 4Runner Wiring.pdf

Excerpt for Taillight and Illumination:

Snagged, thanks Randy! That's way easier to read than the one in the FSM.

Got a new truck yet? Moab in four months...

 

[helo-mech]

Snagged, thanks Randy! That's way easier to read than the one in the FSM.

Got a new truck yet? Moab in four months...

No new truck for me. We are transferring in June. We won't find out where till second week of March. Right now just paying off bills, saving money and cruising around in the Bronco.

I picked up a 96 Corolla about 3 months ago that I DD. Once we have some stuff paid off, I'm gonna look for a nice 1st Gen to DD. The only thing I've been doing with the Bronco is cleaning and fixing little leaks here and there. I did pick up some wheels, just waiting to find a good deal on some BFGs.

 

[Howitzer]

Definitely feel for ya. I spent hrs and hrs pulling out an early '90s alarm system that was already semi-removed. It was a cluster.

As you probably already know, the biggest kicker is the illumination circuit as that goes just about everywhere: radio, dash lights, switches, etc. Hard to isolate and track down.

If you were blowing fuses before and now its no longer blowing fuses but still no power then something else ate itself in the path. Probably a relay. Hopefully, you were putting the right amp rating fuse in each time. Even then, a spike higher than the amp rating can go down the wire before the fuse pops.

What I would probably do is visual checks first:
- trailer wiring, always crappy connections and i've seen more than a few fall loose and short out on the exhaust pipe.
- radio/cig lighter, see above, crappy connections, too many borrowed powers, etc
- front marker lights, esp if someone added fogs, bumper, etc. Improperly ran wires can easily fray on sheetmetal.
- check around the rear cargo light, my PO did a lot of hokey pokey with those wires running power to various things in the cargo area.

If nothing stands out, then start running continuity tests at different harness connections between power and ground. Basically looking for the short. You don't need power for any of these tests. Find the short first, then find out the reason for no power, ie. the relay or whatever else.

Another useful concept to understand is the floating ground concept that the interior lights use. 4crawler has a pretty good write up here when talking about upgrading headlights. Read the paragraph about Implications of Switched Ground.

Toyota 4Runner and Pickup: Brighter Head Lights

Hope some of this is useful to you. If still no luck, you might try reaching out to 4crawler as he is (i belive) also an electrical engineer and is very helpful. He's usually on yotatech.

I appreciate your input, brother! It's been a cold/blizzard snap in Calgary, which as prevented me from doing any further diagnosis, so I'm driving the 03 taco right now to get my mind off of it.
I removed all the trailer wiring that was in there before, and solder-replaced all of the scotch-locks on the circuit, even though it wasn't on the same circuit as the marker lights.

The cig lighter works (the string of curse words as I didn't feel any heat coming off of it so I stuck my finger into it, and yes, that mother is working PERFECT), and doesnt have anything plugged into it, nor are the wires cut or frayed.

It's a stock bumper, but the front end has seen it's fair share of use and abuse, so I will rip it apart with a fine toothed comb, even though I've peeled down the wired a foot or so and haven't seen any cuts or frays. I tested continuity on the marker lights, front and rear, and they tone out fine. I even tore the bulbs out and confirmed no corrosion, and tested continuity.

Luckily, every time I left a junkyard years ago, I would leave with a bunch of relays, so I actually have a spare relay, but have yet to pop it in and test it due to the cold/snow. Ideally id say screw it, I'm a Canadian and that's no excuse, but this is really thick heavy wet snow and I don;t want to get my entire truck sopping wet trying to trace this gremlin out. I have the day off tomorrow, so I will read up on the floating ground writeup! Thank you very much for your help

I'll keep you guys updated. I'm determined not to give up, and I'm determined to figure this out so I can enlighten you all and perhaps help someone down the road. Happy new year, and keep your stick on the ice

Engel

Thank you to Helo-Mech for the FSM,. Now I'm armed with something more than a BB gun in this battle against this beast