When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
hello everybody, i am trying to rewire a 1987 4runner that had the whole rear wire harness removed from dash back...am i wrong to assume that i can run wires straight from the brake pedal switch to a fuse, and then straight to the rear brake light? As for reverse, is it normal to have the light controlled by a wire from the ecu, or again just straight from the wire coming off the shifter (aftermarket floor shifter so has a single wire coming off a switch that is triggered when in reverse) For tail lights, is it normal to just tap off a fuse that is always powered when driving, fuel pump or ignition or something of that nature? Again should that be triggered by something from the ecu as well?
Will the small lights in the rear be too much for these switches, should they all run a relay between each? is it better if i used led bulbs, or is that just putting a bandaid on the problem?
fuel pump and everything needed to run offroad are wired up, and done fairly well...just would like to drive it on the road a bit more
From what I can see in the schematic, the brake lights run from the "STOP" fuse (15A), which is in the left side kick panel fuse box, directly to the switch on the pedal, then back to the stop, or brake, lights, and off them to ground. The fuse is powered directly from the 40A AM1 fusible link, which is in the fuse box in the engine compartment.
The reverse, or backup lights, are powered off the Engine fuse (15A), left side kick panel fuse box, which get's it's +12VDC from the key switch, in the ON position, through the switch in the transmission, then back to the lights. You do need 2 wires to/from the transmission, one with the +12VDC always on it from the Engine fuse, the other to the lights. When you put it in reverse, the switch in the tranny closes, applying the +12 to the lights.
As for the tail lights, they go from the tail light relay, which get's it's +12VDC to power the lights from the AM1 fuse, as above, then it runs through the TAIL fuse (15A), again in the left side kick panel fuse box, then back to the light assy, powering the tail lights, clearance lights, and licence lights. The tail light relay is energized by voltage from the switch on the steering column, again, powered from the AM1 fusible link in the engine compartment fuse box.
Wow, i wish i could say that this is what i was asking for but this is WAY more than i expected to get, youre the best!! This is probably all i need to get it going! The truck has a 4.3 chevy swapped in, so not sure if the factory fuse panel or am1 fusible links are still being used, but this will be a great place to start checking!
are the wiring diagrams you used to decipher this open source somewhere, or did you buy a physical copy/pdf of it? any recommendations on where to look to buy wiring diagrams for these trucks?
from what i can understand from your diagram, the tail light circuit should look something like this: am1 -> tail light relay -> 15a tail fuse -> tail lights -> ground (tail light relay getting 12v from the switch on column)
my two questions i have are: i have always been under the impression that the fuse should go as close to the battery as possible in the flow of electricity. from what i can decipher the relay is between the fuse and battery, is this correct? if the relay shorts out, will the fusible link be enough to break before any damage is caused? i understand the chances of the relay shorting are slim, just want to be sure.
my second question is: what switch do i use for the tail light relay, i would assume its just whatever wire has 12v when in the on/run position coming from the ignition, but again just want to be sure i dont overload any switches.
A picture is worth 1,000 words. Here's a pic of the schematic:
The white wire to pin 2 of the tail light relay, labeled with a C, up at the right side, shown as a white wire (w), is from the AM1 fusible link. See how it not only provides the +12VDC for the relay coil, but also, through the relay's NC contacts, to the relay's pin 3, and then to the Tail fuse.
Thus, they were able to use one wire for two purposes. 1) power the relay coil, and, when the relay is de-energized, according to the schematic, although I have a sneaking hunch it's being shown energized, I'd have to go outside and check mine, and it's in the shop, so I can't, and also, 2) +12VDC to the tail fuse, and thence to the lights. When the relay contacts are closed.
It makes no sense to me that the relay is being shown de-energized, because if it were, the tail lights would be on when the switch is off. The relay would lose it's ground, from the switch, de-energizing it, turning the tail lights on. Also, if it's shown de-energized, as it should be, when you apply ground to the coil, through the switch, it would OPEN, removing the +12 VDC to the lights. It would just drain the battery through the tail lights, when the truck were shut off, and the switch were off. The power, or hot, line, labeled C is directly connected to the battery, through a couple of fusible links. Always hot.
OK, I just checked the troubleshooting for the tail light relay. I was right: It's being shown energized for some reason in the schematic. It should be the contacts, between pins 2 and 3, are open with no voltage AND ground applied to the relay. It has a constant voltage applied to it from the C wire I described above, and gets it's ground when the switch is closed. SO, it's being shown backwards. Energized. The convention is to show relays de-energized in schematics. I don't know why it's being shown energized.
Notice the switch, labeled Tail Light, is on the steering column. The stalk that turns on the lights. Head and tail. It has 2 switches on the stalk, one for headlights, one for the tail lights. Notice that the Toyota engineers like to switch the ground in and out of circuits, not the power. Nowadays, it's gone to most engineers switch hot, not ground.
hmm, definetly helpful but also definetly a little confusing! i think i will just wind up using inline fuses run straight off the battery going to the tail light relay/switch for the lights, and ignore the factory fuse panel.
i am confused about what ive read about the switching grounds, as opposed to switching powers. does this mean i am not able to have a wire with a switch run directly to the rear light, and have that light grounded to the chassis? hope that question makes sense
hmm, definetly helpful but also definetly a little confusing! i think i will just wind up using inline fuses run straight off the battery going to the tail light relay/switch for the lights, and ignore the factory fuse panel.
i am confused about what ive read about the switching grounds, as opposed to switching powers. does this mean i am not able to have a wire with a switch run directly to the rear light, and have that light grounded to the chassis? hope that question makes sense
I apologize! Confusion is exactly the opposite of what I was trying to do.
Yes. If you put in a whole new circuit, for example: Battery>fuse>switch>lights>ground it should work fine. Or: Battery>fuse>switch>relay coil>ground/Battery>fuse>relay contacts>tail lights>ground
Notice that if you use a relay to control the lights, with a switch to control the relay, you essentially have added 2 new circuits. One to activate/deactivate the relay, and one that the relay switches on and off. IE: the lights.
Yes, the relay should be close to the battery. The low power wires to control the relay run from the battery to a fuse to the switch, then back to one relay coil pin, are fine. Just ground one of the relay's coil pins to the body.
When you turn on the switch, it applies voltage to the relay's coil, causing the relay to energize, or switch on. This closes the two contact pins you selected earlier.
Of course, the battery should have 2 heavy gauge wires on the negative terminal. One down to the engine block, normally bolted onto the AC compressor mount, the other to the body. There's a great spot just forward of the battery, behind the headlight for the body ground.
Then, a higher power wire to go from the battery to a fuse, then to one of the relay's contact pins, and then from the other contact pin to the lights.
Make sure you select the pair of contacts on the relay that are "normally open". That means that when the relay is not energized, ie no voltage on the coil pins, the two pins are not connected to one another. They only connect when power is applied to the relay's coil pins. Like when the switch you're using is closed, or turned ON.
yes that is about as clear as it can get! lights are all working fine now, i just ran new wires straight from the battery, working great now! for the once a month i drive this truck on the road that should be fine!
a second, slightly unrelated question. when testing power to the fuse panel for the tail and brake lights, i noticed every fuse is only getting 5-6 volts. should i start tracking down grounding issues (probably a good idea regardless) or is there a resistor in the system somewhere and 5 volts is normal? thanks!
No, +5 VDC is not normal. It should be +12 VDC straight from the battery, through the Main FL, to the 80A FL, to the 40A FL, to the various fuses. No resistors anywhere. Those FLs are bolted into the fuse box in the engine compartment. Every bolt is a chance for rust/dirt/corrosion/oil etc. thus dropping the voltage down. Hot wires are a valid possibilities, but it's unlikely. Unless there's corrosion on the battery terminal, or the wires attached, unlikely, though.
If there's a bad ground some place, that could be the problem. If the ground you used for your negative meter lead wasn't good and clean, bare metal, there's a possibility. If the ground off the battery to where you placed your meter lead, GOOD possibility. Remember, as far as electricity is concerned, if every connection is good, using a section of bare metal on the back of the bed, is no different than putting your meter lead on the negative terminal. Do you see my point there? The trons don't care, as long as there's a good path for current flow.
Remember, 2 vitally important grounds come off the battery negative terminal. One to the engine block, as I've told you about before. The other to the body. Just forward of the battery, just behind the headlight. I changed mine out shortly after I bought the 4Runner, around 1990 or so. There was maybe a 8GA or 6GA (smaller the number, bigger the wire, up to a point) on there. When I went to the Marine terminals (best move I ever made I think), I put 2 new wires on the battery negative. 2/0 stranded wires. Pronounced two-aught. Bigger by far than what was on it before. a bit smaller than about 1/2 my pinky finger (I have fat fingers!). I also cleaned the heck out of the points those two wires went to. Bare metal under the ring terminals, which took a little paint removal.
The tail lights ground to...the body. The backup lights ground to...the body
See a pattern developing here? Did you carefully check the ground under the left kick panel? The one with a number of wires all crimped together, then to the ring terminal that's bolted to the...body Also, check the grounds under the tail light assemblies, which the 3 bulbs in the assembly, brake, marker, reverse, all use. That ground rusts up pretty easy, and rust is a great resistor. Not real precise on the ohms, but darn effective
I am glad you got it all going right again. Electric circuits aren't really as complicated as people think. Electronic circuits can drive you batty, but electrical, not so much. Pretty straightforward. 2 ends, power and ground, maybe a switch in the middle, maybe a relay too, and then a light, or fan, or whatever.
you win again, thank you so much!! this truck hasnt had the nicest life for the past few years i think, alot of questionable connections so im just going to go ahead and redo the whole system, i will check the voltage with every change i make and let you know what makes the most difference! Good reminder to check how the bolts look that hold the FL in place.
i didnt know about the ground under the left kick panel, i will take a look at that tomorrow
"Electronic circuits can drive you batty, but electrical, not so much" thats a good line, ill remember that
01-02-2021, 10:09 PM
