Where is headlight ground on 1990 4Runner SR5?

Headlight ground may be at the headlight switch, many Toyotas switch the -ve instead of the +ve.

Wouldn't the HIGH beam be out too then? I bet it just a corroded connector or pin on the back of the bulb. Clean it with some sand paper and bet it will work again. Can't you unplug from in the engine compartment (can on my

Wolfgang,

What you wrote makes sense, but that's not what is happening.

As I stated, there are no low beam lights for either the vehicle or the plow for that matter. Only the high beams work for both and are switched by a toggle switch located inside the vehicle.

I should also mention that there is no blue high beam indicator. From what I've learned so far, it is somehow connected to the low beam circuit. Don't ask me why though. That is how I'm able to tell that the low beams are working again because, on occasion, I'll see the blue high beam indicator light and try the low beams. They'll work for a short while and then quit again. This is usually either during or after a heavy rain, which is what makes me think that the "bad connection" is getting wet and completing the circuit to make the low beams work. I assume it's grounding by getting wet, otherwise I would expect it to blow a fuse if it were shorting out. In any case, they still don't work and I'm not any closer to solving the problem.

As for under the hood, the battery is in the way on the passenger side of the vehicle and I have to remove the overflow tank on the driver's side to barely gain access to the headlight connector there.

Thanks for responding.

If it was my truck and I did not install the plow I would trace the wiring that was installed for the plow lights.

I had a truck that had a trailer plug that did not work, found 4 splices in the wire between the cab and the bumper, they were all corroded.

Mike

I too am having the same problem on my 84 SR5 and it has a plow attached. It was designed so that the ground is the dimmer switch. As often happens with foreign vehicles, Toyota powers the headlights backwards from Chevy, Ford or Dodge. There is a headlight relay in the fuse box just behind the battery: it supplies power to the lights, then the dimmer switch grounds either the low or high side of the lights. Somewhere in the circuit there is a self-resetting circuit breaker. The book I have does not show it and I have not been able to locate it... yet. I have a new set of plow lights I am going to install and in doing that may shed more (no pun intended) light on our problem. The way the wiring is now, for my plow lights, looks like spaghetti. I am hoping to clean that up when I install the new lights. Also need to consider the switch for changing from plow to truck lights -- if that has corroded contacts inside.... To see if my power relay is the problem I have also purchased a

Jlsuther,

Thanks for responding.

Since my problem began, I've replaced the headlight switch, turn-signal / dimmer assembly, and even the toggle switch that switches between the vehicle or plow lights.

When I first began troubleshooting the problem and had everything apart at the steering column, it gave me EVERY indication that it was a bad switch. I could get the lights to work and make them fail again by playing around with the switch. So, I ordered a new one and replaced it, only to wind up with the same problem. That made me think that moving the switch may have actually been affecting the turn-signal / dimmer assembly, so I tore it all apart again figuring that it had to be due to something in the steering column. Replaced the turn-signal / dimmer assembly and still had the same problem. Tracked down a new toggle switch for the plow lights and put new quick connect terminals on all of the wires. Still only had high-beams on either the vehicle or plow lights. It has been like that ever since with the exception of the low-beams working after a heavy rain as I described in my original post. That's why I don't think that the problem is in the steering column, but rather under the hood or vehicle somewhere.

On another occasion, I started tracing the wires back from the plow toggle switch to see if I could find a loose or broken connection. No such luck. I even went as far as disconnecting the plow lights just in case they were possibly causing the problem. That didn't correct it either, so I put it all back together again. I even traced wires up under the relay box where the headlight relay and fuses are located. Everything seemed fine there too.

Coincidentally, a day or two after I posted here, my plow high-beam lights quit working. I checked fuses etc. They were fine. So, now I only have the vehicle high-beam lights working and nothing else. Very frustrating. At this point I'm really stumped.

I looked in my Chilton's manual (1989 - 1996 Pick-ups/Land Cruiser/4Runner ), which leaves a lot to be desired, and couldn't find any headlight circuit breaker listed. If you have a Canadian Model 4Runner, the manual shows a Dimmer relay located just above fuses 1 & 2 in Relay Block #2. I don't know if that helps you or not, as there isn't one shown for the Pick-ups.

Out of curiosity, how did you wire in that 30A relay from Radio Shack? That's the only part that I haven't replaced yet. I know that it's operating and I believe that the contacts are okay, but at this point I'm ready to try just about anything that might help to FIX this once a for all.

If I solve this problem or make any progress, I post it here. Good luck.

Peter.

The relay I have from radio shack is part number 275-226.

What I have done is removed the connectors from the fuseblock by straightening the locks on the connectors disconnect the battery before doing this. Since two of the connectors come directly from the battery I will put some heat shrink tubing over the metal connectors to insulate them. If the wires come loose from the relay and touch anything metal it could start a fire.

Then follow the wiring diagram on the back of the new relay package (the wiring diagram is also on the top of the relay) and plug the wires into the new relay. To finish use several wire ties to secure the relay to the fuse block.

If this dosen't fix the problem and I want the origonal relay back I will just remove this relay, cut the heat shrink tubing from the wire connectors, bend the locks out and push the wires back into their origional slots in the fuse block. Then I could plug in the original relay.

Hope this helps, and thanks for telling me all the things you have tried. Will let you know how it goes. Jim

To answer your original question where the ground for the headlight switch is.

It is next to your left foot when sitting in the drivers seat. remove the plastic panel below the fuse box and you will see several white wires with a black tracer bolted to the body near the fuse box.

The ground wires coming from the headlight switch and the dimmer switch are wite with a black tracer. I have the plastic off my steering column and have unplugged the wire connectors for the light switches. The only white wire I see is a heavy one. Then on the other side of the connector there is a skinny white wire with a black tracer that goes over to the ground next to the fuse block.

It seems the headlight and dimmer switch are both grounded through that one wire.

I like the heave wire comming from the switches but that skinny one looks silly.

a possiable theory... The headlight switch is a ground for the headlight relay so does not have much amperage going to ground through it. The dimmer switch is the ground for the larger current going through the headlights. both of these grounds are going through the heavy ground wire attached to the headlight switch and the dimmer switch. Then through a connector into a skinny wire and to the ground by the fuse box. If over the years corrosion has entered into the body and thet skinny ground wire the current for the headlights will start to equal the current coming through the headlight relay and allow the relay to open.

I know I can go on at times!

My plan for this is to remove some insulation from the heavy ground wire coming from the light switches, solder a heavy wire onto it and run my new wire closer to the battery ground.

I have not had a chance to do anything on the truck today, busy with christmas shopping. My weekend is tuesday and wednesday so I plan to work on the truck then.

Jim,

Take a look at the following link:

Also take a look at the "Combo Switch Repair" item. I tried this a while back, before I replaced the assembly, again without any success. My contacts didn't really look bad though, but I figured that it couldn't hurt to try to clean them up a bit.

Hope this may be of help to you.

Peter.

Just took a 5 mile drive and my lights stayed on.

I changed the lights and looked closer at the wiring. Someone used scotch locks to connect the truck headlight wiring to the plow wiring. I replaced the scotch locks with regular crimp type connectors. I have also added the ground wire I mentioned earlier from the light switch ground to the ground next to the fuse block in the cab. Then ran a ground wire from there to the fender where the battery negative cable attaches. I know it was just a short trip but I am hopeful.

Jim,

Glad to hear that your lights are working.

I opened mine up again last Tuesday and discovered that what I had thought before to be the splices into the vehicle's low and high beam circuits were actually tied to the plow lights. Digging a little deeper, I found the connections under the driver-side fender. They were right behind the harness that comes from the plow light toggle switch in the cab and were taped up so well to the factory harness that I didn't realize that they were there the last time that I took everything apart. Upon inspection, there wasn't anything noticably wrong with the connections other than them being Scotchlocks. I replaced them with crimp-on butt splices, then wrapped it all up and added some split wire loom over it to protect it. I now have both low and high beam vehicle lights along with the blue indicator. That's the good news.

The bad news is that I still don't have any plow lights other than the parking and turn signals. Upon testing at the DPDT toggle switch (6 terminals) in the cab, where I determined that all of the wires were in their correct locations, I was able to surmise that I must have an open in the plow light circuit. I have around 9V showing when I put a VOM meter on the wires feeding the plow lights, but it's not enoguh to light a simple 12V test light. There is one more wire (white) that is external to the plow light harness and according to the wiring diagram is typically supposed to be grounded. That, I believe, would be the case for an American vehicle, but, as you stated, Toyota does it differently. They switch ground to the lights instead of power. That said, I expect to find yet another Scotchlock bugged into the wire under the relay housing in the engine compartment, where the headlight relay and fuses are located. I haven't had a chance to check it yet as it's been pretty cold. When I do, I'll post back with the results.

Peter.

You are right about 9 volts being too low for the headlights. Good luck finding the other schotlocks, and warmer weather to work in. Hope to hear good news from you soon.

The next project I have on mine is the front axle seals.

Jim,

Problem solved. The white wire that is external to the plow light harness was Scotchlocked to a wire under the relay box. Again, it didn't "look" bad, but I removed it anyway and then soldered the wire in place along with some shrink tubing to protect it.

I now have both low and high beam plow lights! Everything works fine, even the blue indicator.

As I understood it, you were able to fix yours by replacing them and adding new ground wires as you mentioned in one of your previous posts. Hope you have continued success.

Peter.

Good to hear your truck is fixed. Yes, my lights are working now too. So much for high payed mechanics using scotchlocks to get the job done faster.