squ

The top row of the rear combination lights (Grey connectors, a total of 4, 2 on each side) of my 93 ES300 doesn't light up, I've checked each of the 4 bulbs and all of them seem fine. Does anyone know how to diagnose the wires?

I'm going out to buy a multi-meter to make sure each of the bulbs have continuity, but as far as the wires are concerned, I think all of them are connected in series, which means if one of the live wires is dead, all of them would be dead (hence none of the bulbs light up), right?

I hope someone who had similiar problems could help me out, thanks a lot!

ESPilot

Hey Squ,

You didn't mention whether or not the bulbs light when you brake? I'll assume that they do, and that this is only a parking light issue. You also didn't reference a warning in the instrument cluster. Usually if there is a bulb out or a short circuit, the car detects a change in voltage and gives you a heads-up. If you aren't getting a warning, I'll have to dig deeper to offer suggestions. Anyway, here's what I can come up with for now.

If they are all out, as you say, the bulbs are not the problem. There should be three bulbs per taillamp that light with your parking lights. The bulbs in each lamp are actually wired in parallel to each other. This provides a way for current to reach the other bulbs if one bulb burns out. The taillamp assemblies are also "in parallel", meaning that a single power wire travels to the trunk, and then it splits into two wires, with one going to each assembly.

First, check the fuse (the box is under the dash on the driver's side). The taillamps run off of a 15-amp fuse; it's in the middle row of a group of twelve fuses. There's also a taillamp relay on the backside of the same box. It's the middle one of three similar-looking relays with contacts numbered 1, 2, 3 and 5. The relay should be closed (i.e. no resistance) with the parking lights switched on; touch your ohmmeter to contacts 3 and 5 to test for this.

If the fuse is intact and the relay appears to be operational, you'll have to work your way forward from the taillamps toward the fuse box, checking for voltage while your parking lights are on. The harness runs up the left side of the car. According to the wiring diagram, the wire is green all the way from the taillamps straight to the fuse box.

Good luck and have fun! It's always so satisfying when you can find and solve this kind of problem instead of giving someone else your hard-earned money!

squ

ESPilot, Thank you for your informative response!
I'm sorry about the missing information, here are the blanks:
1. The bulbs do light up when I brake. These are the bulbs with 2 wires inside, they are with with the black connectors. These bulbs work perfectly as well, meaning they light up when I turn the combination switch to either parking light only or headlight mode (light through one of the wires inside). These are not the problem, the problem is the grey connector ones (2 bulbs on each side), with a single wire inside.
2. The warning light in the instrument cluster do light up, and they've been lighting up for quite some time now. I replaced 2 faulty side marker bulbs (the 168 wedge ones) and they work fine now. When I turn the combination switch to parking light only or headlight mode, they do light up.
So basically all lights on the bottom row (black connector ones) work fine, just the top row (2 on each side) that's the problem.
I've bought the multimeter and measured all 4 bulbs, like you said, it's not the bulbs' problem. All 4 are fine. And not surprisingly, there is no voltage between the + and - of each of the connectors where the bulbs go.
I will take your advice and check the fuse and the relay.
When you said the wiring goes alongside the left of the car, that rang a bell. My left rear power window is not working as well, when I hit the switch (from the left rear door or from the driver's door), I hear the motor but the glass doesn't move. Maybe these 2 problems are related...
Anyways, Thank you so much for the reply, I'll certainly keep you posted of how I go.

Cheers,
Sean

ESPilot

Hmm, tricky. Since I don't have a 92-96, I can't see how things look, all I can do is look at wiring diagrams and they aren't helping me much. If only part of your parking lights are out (the top row, as you said) I would be suspicious of a break in the wiring harness somewhere right around the left taillamp assembly. Trace the wires from the "dead" bulbs and see where they join with the power wire for the lower row of parking light bulbs that IS working.

I can't say for sure, but it makes sense to me that all the parking lights, including wedge bulbs, etc, will run off of one circuit, so if the others are working, it probably isn't a fuse or a relay. However, the fact that several bulbs at the same end of the car ARE out indicates to me that there is some single point where the circuit has been broken--meaning, a connector is disconnected or a splice was pulled apart somehow. It's probably in the trunk, near the left taillamp, since that's where the power wire divides and goes to the top and bottom rows of the left and right taillamps.

Good luck, and don't take what I'm saying as gospel--I'm just trying to interpret wiring diagrams!

squ

Thanks for the reply, ESPilot!
I'll take a look when I get a chance, probably some time next week. Will let you know what I find.