My left rear tail light has water in the lens

This is a typica grounding error. You should try to add a good ground cable to your tail light. Sound strange but this often solves such issue:)

Voltage for the tail lamps shows to be a brown wire. Use a test light, check that wire for voltage, headlamp switch on. If voltage then check black ground wire.
A problem with grounds will cause some weird things to happen. Ground wires are black. You can use a test light to check ground, one end of testlight comes from battery voltage, the other end you touch ground, black wire, you have to penetrate the insulation. If the lite comes on, at least the ground is good enough for the test light.
At the moment, I don't care about the maker lamps. I do care about tail--stop--turn--tag lamp. In the past, I have been stopped because of no tag light.
Just my opinion.https://s9.postimg.org/af5e5kqtb/tail_lamps.jpg
Click on the link, hope you can read it.

Error logs are a great thing. They will help you find intermittent problems and start you off in a general direction of where a problem could be. There is a great level of detail on the justcommodores site on checking error codes logged by the engine management system, but this does not detail anything about the abs system. The abs warning light is not as common as the check engine warning light. Reading through the posts, I haven't found any detail on checking error codes logged by the abs system.

So here it is. For those of you familiar with checking the engine error codes, this procedure is so simple its not funny.

Basically, to check the engine error log, you bridge the 5th (ground) and 6th pins in the ODB connector under the steering wheel.

To check the ABS error log, using the same trusty calibrated paper clip, you simply bridge pins 5 and 12 of the connector.

To find pins 5 and 12, start at the top left hand corner. That is pin one. Going to the right, you count pin 2,3,4 etc. Once you get to the end, jump back to the start of the bottom left level of pins and keep counting. Pin 5 is about halfway along the top row, pin 12 is a little left of the middle in the bottom row.

Reading the error codes is the same procedure (counting the flashes), except now, the ABS light flashes (as opposed to the engine light when checking the engine codes).

The ABS log also uses code 12 firstly, with any errors logged shown after that. If no errors are logged, the 12 will flash again.

Error codes for the ABS error log (VR/VS) are as follows:

12 Diagnostic system operational
21 Right hand front wheel speed sensor fault
23 Right hand front wheel speed sensor continuity fault
25 Left hand front wheel speed sensor fault
27 Left hand front wheel speed sensor continuity fault
28 Wheel speed sensor frequency error
31 Right hand rear wheel speed sensor fault
33 Right hand rear wheel speed sensor continuity fault
35 Left hand rear wheel speed sensor fault
37 Left hand rear wheel speed sensor continuity fault
41 Right hand front inlet solenoid valve circuit fault
42 Right hand front outlet solenoid valve circuit fault
45 Left hand front inlet solenoid valve circuit fault
46 Left hand front outlet solenoid valve circuit fault
55 Rear inlet solenoid valve circuit fault
56 Rear outlet solenoid valve circuit fault
61 Pump motor relay circuit fault
63 Valve relay circuit fault
71 ABS control module internal fault

The above guide has been verified on a VR/VS. Checking the error log on all models prior to VR/VS is the same for the engine log, and I would assume that the same can be said for the ABS log, would be happy if someone could verify this for me.

use a light circuit breaker in place of the fuse, then check harness for short to ground, start with tail light harness, or trailer wiring if so equiped

not sure of the vehicle but it sounds like a ground problem,
you have power back there it sounds like and if a ground is
bad the power will ground thru another bulb filament.
A clip lead to a good ground to a tail light ground circuit
will confirm. As close to the bulb as possible.

Replace right rear tail light bulb holder. Bad ground.

I have not heard of this before and I am unfamiliar with your vehicle. In most vehicles, if your dash lights are not working your tail lights are also not working (they are on the same fuse). This means whenever your dash lights out, your tail lights are also out, which could put you in the position of getting rear ended by another vehicle or getting a ticket if a police officer see's your tail lights are out at night. It sounds like you are dealing with a loose or broken ground wire. I would start by checking all the tail light wire connections and ground wires located in the back of the vehicle. I have seen ground wires held together by a screw attached to a plastic tail light housing. When the tail light housing breaks it causes an intermittent connection (dim lights, out lights, etc.). A careful inspection of the wires, connectors, and ground wires may turn up the cause of the problem. A simple dab of molten solder, a piece of electrical tape, or a longer screw may be all you need to fix the problem.

sounds like you may have a hitch installed on your vehicle and the ground wire between it and the taillight is damaged. if it doesnt have a hitch the most likely cause is still a ground at the rear of the truck on the frame rail drivers side where the factory wiring is located for the trailer plug. this is a common issue. i hope this helps

Almost certainly a bad earth in your left hand rear light somewhere.
Clean the earths up REALLY well, ( like silver shiny metal ) and put a new end on the wire to be sure.
You can test it by grounding one end of an extra wire on a really good contact point on the chassis and getting someone to hold the other end on the common earth contact for your rear left blinker, stop light, reverse light and tail light while you try it again.

Definitely not getting a proper earth somewhere.

I have also seen a whitish corrosion on the bottom of the bulb itself, and in it's socket, cause the exact same symptoms.

If there is evidence of water in the taillight lens, go for the bulbs and their sockets first. Clean, clean, clean.

CHEVY S-10 TAIL LIGHTS PROBLEM RESOLVED...It seems Chevy engineered a ground shorting clip located under the left rear bumper area. It looks like a connector for trailer wiring harness, but in actuallity is a metal shorting clip which ties 5 wires together. They are all the ground wires for the tail lights. Then one single small wire runs to ground completeing the circuit. Problem is that this one wire is not tough enough to be a strain relief for the grounding plug and over time the ground wire wears, leaving intermittent lighting problems. FIX IS TO SPLICE THE GROUND WIRE INTO ONE OF THE FIVE OTHER WIRES AND USE PLASTIC TY WRAP FOR STRAIN RELIEF. This fixes no tail lights, intermittent rear signals, and other significant problems. I just got done making this same repair on a 2000 s-10 and everything works fine. Since it is the strain on the single ground wire connected to the connector that leads to failure, it is best to tie a new ground or clip the ground wire coming out of the plug and resplice it into one of the other five wires. Does not matter which one since electrically it makes no difference; they are all gound wires. BUT only one wire completes the connection and that is the problem. Really good engineering Chevy! The location is under left rear of bed in wiring harness right before the split. The connector is blue or green. Take the cover off to see the metal shorting clip. Also note the ground wire coming out of the plug/connector and runs about 8 inches to frame. If this is not hooked up you will have tail light issues. If you register on Autozone .com you can access wiring schematics for free. BL