FREAKINHEAT

I'll have to look again, but I believe that there are 2 brown and 1 green that goes into the left furthest socket. If I connected the two brown together, shouldn't that continue the ground? I did that already and that didn't work.

WallyP

You need to do whatever it takes to get a good ground on all of the brown wires...

Alan

Is this in the '88? or the '91? (you need to tell us every time what year)

'88 is fuse #40 (#12 & #13 are irrelevant)

'90 is fuse #7 (#12 & #13 are irrelevant)

Start with the simple things: totally ignore the rear lights you know have issues - get the front/side markers working - if the front/side doesn't work the rear never will either.

Once the front/side works you can presume the rear loom has power too and can start implementing actual fixes...

Alan

Eplebnista

FREAKINHEAT and I took a run at this today.

There is continuity from the bulb control connector out to all the lights and the disconnected ground wire for the mangled socket has continuity to ground. Thanks to my power probe 3 and the wiring diagram, I think we got all the lights to illuminate from feeding power to the appropriate pins on the bulb control socket.

I am hoping it is the bulb control module. We ran out of time and I kept the module and just hit all the solder joints with my trusty micro tip soldering iron. We will keep our fingers crossed until there is an opportunity to pop the bulb control module back on...

The Power Probe 3 is an awesome electrical troubleshooting tool....

FREAKINHEAT

A thousand thanks to Eplebenista! He truly knows now, my total lack of understanding of the electric world. Great garage and tools!

Love the community support!

Fingers crossed

FREAKINHEAT

Ok so I purchased a used bulb control unit and still the same issue. I turn on the lights, no rear tail lights at all. I press on the brakes, and the upper middle and two inner lights come on. The drivers side markers still do not work, while the passengers do.

Any suggestions on why the lights do not come on at all, unless I hit the brakes?

Alan

Do you know that you have power to the fuses & out of the fuses that feed the bulb control module (see above post). You can test with a DMM probe to the fuse. There are dimples on the exposed end of the ATO/ATC fuses that allow you to probe the fuse terminals while it is in circuit. The bottom is the fuse output (on '85+ cars). Test WRT ground (like the body of the cigar lighter). Fuses should be active only when the lights are on.

Alan

FREAKINHEAT

Alan,

If the bulb control unit wasn't getting power, wouldn't the brake lights not work at all?

I will test the fuse/area gain to see if that's the issue.

mickster

Dumb guy in the room but there are a bunch of relays besides the fuses that act to turn the lights on and off as well as the turn signals. Any chance of a bad relay? Sounds like a ground issue but...

Alan

It doesn't work that way... all lighting circuits are unique and independent in the bulb control unit - power to the bulbs just passes straight through from the fuses.

All that is in the bulb control unit as far as the lights are concerned are very low value series resistors - they very rarely go wrong that affects the light working (except loose connectors). What usually fails (or at least causes issues) is in the monitoring section causing false warnings, this has no effect on the lights themselves.

BTW there are also no relays involved here for the marker lights or brakes.

You need to do as I said and test the power in to the bulb monitoring unit from the fuses - nothing in - nothing out.

Alan

Mrmerlin

please tell us the year of the car your working on.
Please post pictures of the light housing and the associated wire looms.
Follow Alans advice to the letter, do the testing he is asking you to do
Otto is a great resource, see if he can assist you further

Eplebnista

The car is a 91. I agree that the next step is to check for power at the bulb control connector and fuses etc.

While the bulb control unit has no relays and is basically a bunch of resistors, induction coils and reed switches, I had an intermittent tail light failure that was fixed by reflowing all the solder joints in the bulb control module. I did the same with Freakinheat's bulb module after he left it with me to diddle with, but that obviously did not fix his issue.

Are there really fuses for each side of the car?

Alan

Yes there are fuses per side - see the diagrams. L & R marker lights are two different circuits (e.g. parking lights).

On a '91 - there are just "resistors" from in to out, and here when I say resistors I mean strips of folded metal.

Semiconductor comparators test the voltage dropped over these resistors when the lights are active and therefore can determine if the current level is in the right range. Your description is accurate only for the earlier style bulb control units before these were redesigned.

You are certainly right that solder joints can still go bad, but seems it wasn't that. Always start with the most likely, easiest and cheapest things to check/replace. Fuses are right up there at the top of that list.

Alan

mdkelly1

Alan is giving good advice.

As mentioned, the last time I had the lights out on one side, it was a blown fuse. It was a very long time ago (16 years), so I don't remember which one it was, but I went to the fuse chart and mapped it against those in the CE panel to find the right one.

That fixed the problem with "all lights out on one side." That was the beginning of my education about lights, bulb values, fuses, corrosion resistance, pin & socket cleaning, and the need to take it step-by-step when trying to trouble shoot an electrical issue, especially with the lights.

Just finished with a passenger headlight issue and it was the same process, obvious things first, then the more complicated.

FREAKINHEAT

Fuses are the cheapest thing to replace, so I went back through and............... This is what I found. Fuse number 7!

I am still no longer with the outer tail lights since the PO hacked them, so I guess we need to find a suitable replacement from the nissan or napa parts catalog. I cut the drivers out and reattached the two brown wires that lead to the socket to each other, to keep the ground loop continuous.