Reverse Lights Not Working. Electrical Confusion.

[Kurtatron]

Car in question is a 1999 Toyota Solara Manual Transmission. Both lights are not functioning when engaging the reverse gear. What I have done so far: I took a multimeter to the reverse switch on the transmission. Found no continuity in the switch when in neutral. Shifting reverse completed the circuit and gave me continuity. Is that enough or should I be checking for resistance or voltage? Both bulbs looked ok. The bulbs had continuity also. I also checked the fuses in the cabin. I couldn’t find a fuse for reverse lights specifically, but I checked them all anyways. I could not find a busted fuse. Any ideas where I can look next? This is frustrating me. Thanks.

 

[anpconnors]

next steps would be to verify you have 12V present at the reverse light switch, then get a wiring diagram and trace the wires to make sure they have continuity. Check the ground connections near lamps too. check socket connection for corrosion. wiring diagram may be available at www.mel.org then databases then Chilton, you will need a library card or search online. good luck.

 

[nthach]

Older Toyotas used a taillight "fail" relay as well that lights up an idiot light to check the taillamps - might be worth checking out.

 

[exranger06]

Here's a wiring diagram BTW, you can find these wiring diagrams for pretty much any vehicle for free at BBBIndustries.com

 

[Kestas]

Do the wires feeding the backup lights flex at the trunk hinge? This is another weak point I've dealt with more than once.

 

[Johnny2Bad]

You should check the integrity of the wiring to the backup lamps. Easiest way is to construct a test lead long enough to easily go (no stretching or tight bending) to the transmission switch or fuse block. Ideally you would put an alligator clip on one end, you can leave the other end bare, and just use your DMM when at the rear / open trunk of the vehicle. But if you secure the bare wire with electrical tape instead of an alligator clip, that should be fine, it's just that less secure connections when they are remote can be problematic so insure you have a good remote connection. Any wire long enough you happen to have around will be fine for the voltage and continuity tests you will make in automotive troubleshooting. If you don't have any, buy some cheap trailer hookup wire (so-called "Primary Wire") at an auto parts store or hardware store. Any reasonable size (gauge) will do for the brief testing you will perform. Suggest 18GA. You should see the expected result (12V across the terminals for each lamp, or none across the terminals) with the two modes (reverse selected + some other gear / neutral selected). If there are two lamps, check across them (ie check the positive terminal at the L side lamp and the negative terminal at the R side lamp with both lamps installed in the sockets). In some cases a lamp failure on one side will kill both lamps. Removing the lamp housings (they should attach with removable connectors of some kind) and giving them a good cleaning can often fix these kinds of mysterious auto lamp issues. It can be the problem even when your continuity tests say it shouldn't be. Just not worth it to be chasing down some phantom issue when you can start with the cleaning and know for sure. Hunting down and fixing electrical gremlins only happens two ways. Either you follow a comprehensive checklist of steps or you are experienced at it and your intuition and observation can often quickly find an issue. But even an experienced troubleshooter, if his instincts don't pan out quickly, will go back to the step-bu-step procedure. So that's what I recommend you do.

 

[nthach]

Originally Posted By: Kestas

Do the wires feeding the backup lights flex at the trunk hinge? This is another weak point I've dealt with more than once.

Very common on the Lexus LS400 of that era too - the light wiring fails in the hinge causing all sorts of weird to happen, since the wiring is in the hinge itself. I'm not sure if Toyota went to the extreme of routing backup/plate/tail light wiring in the left trunk hinge as they did on the LS with the Camry platform - if you see a black plastic channel run cover on the trunk hinge it might be worth opening that up.

 

[Kurtatron]

Thanks for the help guys. That wiring diagram helps. I tried digging in deeper. The mystery continues. I measured the voltage at neutral switch. The wire side measured a voltage of 12 volts. The switch itself was ok. I decided to measure the bulbs themselves. I removed the bulbs and measured the contact voltage. The voltage when the transmission is in neutral is zero, but when the transmission is in reverse, the voltage is 1.8 volts and 0.9volts. Is this the problem? Too low a voltage? What could be causing it? I checked the hinge area. I don’t think the hinge area is the culprit, because the Solara reverse lights are not on the trunk lid. I believe the Camry of the same year had the reverse lights on the trunk lid. Would the reverse lights being on the fender still be a likely cause of lighting issues?

 

[mk378]

You should have 12 volts on both wires of the switch (ie 12 volts from either wire to ground) with the key on and transmission in reverse. If there is voltage at the switch but not the bulbs, the wire is broken somewhere along the way.

 

[Kurtatron]

Update: I have done some deeper searching. I took apart the back seat so I could look at the wire and the ground location beneath the trim. The circuit diagram Posted earlier showed the ground being buried under trim of the center pillar. I couldn’t find any deformed wires or corroded ground. So I am getting more desperate. I started taking apart the trim underneath the steering wheel, and then disconnected every connector that had the same color as the reverse bulbs. I ended up finding the correct trrminal that powers the reverse lights. I engaged the reverse gear and checked the voltage, 0.92 volts! That means all the wiring from the dash to the reverse lights is ok. No voltage drop from the bulb to the terminal underneath the steering wheel. This is bad. That means my problem could be underneath the dash or in the engine bay. Out of desperation I tried to eliminate the reverse switch. I sprayed some brake cleaner. Nothing, didn’t work. I dreaded the idea of searching for a broken wire amidst the big V6, and underneath a dash, so I wanted to double check the switch. I tested this time for resistance instead of continuity. The switch in the closed position measured 310 ohms. Is that way too high for the switch? Please tell me it is. I really hope this is a switch problem, Not a wiring problem

 

[VeryNoisyPoet]

Quote:

The switch in the closed position measured 310 ohms. Is that way too high for the switch?

Way too high! A switch should have essentially zero resistance when closed. Test for voltage between the input and output side of the switch with the key on, the transmission in reverse, and the reverse light bulbs installed. A good switch will show very little voltage drop (less than 0.1 volts). If you see more than that, likely the switch has failed.

 

[exranger06]

^^I agree you should do that test. You can also unplug the wiring from the switch and short the two pins together on the wiring plug. The reverse lights should light up (make sure the ignition is on). If they light up, the wiring is fine and the problem is the switch. If they still don't light up, it's a wiring problem.

 

[nthach]

Are you getting voltage at the bulb sockets? If the trunk to passenger compartment connector checks out, it could be something local to that harness.

 

[mk378]

When there is not a moving part involved, broken wires are unlikely. Test the bulbs and reinstall them. Then jump the switch.

 

[SHOZ]

What is the voltage coming out of the switch when in rev, same as going in?

 

[Kurtatron]

Originally Posted By: exranger06

^^I agree you should do that test. You can also unplug the wiring from the switch and short the two pins together on the wiring plug. The reverse lights should light up (make sure the ignition is on). If they light up, the wiring is fine and the problem is the switch. If they still don't light up, it's a wiring problem.

This was the correct step. I took a paper clip and shorted the reverse switch connector. The lights snapped to life. Dang. If only I had tried this before taking apart the trunk and interior. I will put everything back together on Saturday. At least replacing this switch is extremely easy. It’s not under the car, or burried underneath something, a straight shot. I wish other jobs were as easy. Lesson learned. Try the easiest stuff first before pulling things apart. Thanks for the help everyone!