Issues with Rear Parking Lamps


New Member
Oct 14, 2023
I'm trying to get my GN back on the road again. I doing a pre-state-inspection check and everything seems to be good EXCEPT for one annoying issue.
==>The rear taillights/parking lamps do not light.<==
Turn signals work (front and rear).
Headlights work (high-beams as well)
Hazzards work (front and rear).
Brake lights work.
Parking lamps (front headlamp bezel lamps and lower front bumper lamps) go on with either the switch setting in the parking light position or fully on with the switch in the headlamp position (this leads me to believe the switch is good or I wouldn't have front parking lamps either?)...
==>but the rear lights do not light up (neither the little middle lamps nor the larger brake lamps) with the switch in either position.
-- the tail lamp fuse is good (I think there is only one 20A for this?).
--I tested both little bulbs in the rear and both are good
-- I made sure the grounding screw in the driver's side rear trunk area is good.
--I get 12V on the brown wire in the trunk harness when the parking switch is turned on (I think this is the parking lamp voltage wire). I get no voltage when the switch is off.
-- the rear lamp connectors in the trunk look clean .
--With the switch off, I tested one terminal in the small bulb socket and it has continuity to ground and other continuity with the brown wire.
==>but when the parking lamp switch is turned, on BOTH sides of the small lamp bulb connector read 12V.
--I tried "forcing a ground" to the one side of the socket with the switch on, but that didn't work either.
I can't find my service manuals with the wiring diagrams, so I'm at a bit of a stand-still.
My car is scheduled for inspection on Wed, so I need to figure this out and I'm not sure what to do next.
Any help will be much appreciated.

There's a connector in the trunk drivers side rear that has the brown wire passing thru it. C320 separate it and read for the parking lamp voltage there.
Thank you. I found that manual after I posted. Thanks for the clear diagram as well! The brown wire I'm referring to is the (BRN) brown wire in circuit (C320), so I'm testing the correct wire. It goes high (12v) when the switch is on, but no lamps light. Like I said, though actually when the switch is on, BOTH terminals in the lamp socket go high. This is not what i expect. I expected one to stay low (Grd). I removed all of the other bulbs (except one small marker bulbs) on both sides, but it still does the same thing. BTW: This is not a hacked car (has stock wiring). I'm missing something somewhere. I was thinking about disconnecting the connector in the truck and then jumping just the brown and ground wires just to see what happens. Thoughts?
Wire up a 12 volt lamp I use a trunk light bulb with two wires soldered onto it, it will draw about 1 amp and light up bright.
Disconnect the connector C320 and put one bulb lead there on the brown wire and the other to a good ground in the trunk to see if it lights up brightly with the parking lamps ON.
The black wires in the lamp sockets should be a good ground connection make sure the ground black wires are good going to the lamp sockets and the ground screw.
If both terminals go high you don't have a good ground on the black ground wire(s).
There are splices in the harness for the many grounds and the screw itself as shown below.
Check G177 ground screw first.
I was/am thinking bad ground also. I tested the G177 ground and it seemed ok. I tried forcing a ground to the ground side of a bulb socket also, but no difference. I hooked a meter to the brown wire with the switch on and I get roughly 12v, but I'll also try a bulb. I'll let you know the results. I think I'm so close to getting that car back on the road....just this one annoying issue and a difficult time tracking it down. Thanks again for all of your help so far.
Hi. With the (C320/S360) hardness connector in the trunk, disconnected, I get 11.7 V on the brown wire when the headlamp switch is turned on (either position). Off I get nothing. When on, I can light up a large bulb with it. To do this test, I connected to the brown wire inside the disconnected harness connector (C320/S360) and to the ground clip (G177) (Note: I did not connect to the screw mounted to the trunk body thinking the screw to connector connection may be bad, so I went directly to the copper connector itself.
If I test one of the small bulb sockets in the rear taillight assembly, I get ground continuity on BOTH sides of the socket connector regardless of whether the switch is on or off. I tried providing an alternative ground to the black wire side of this bulb socket. No difference. No lights. I also tried to provide voltage to the brown wire side of this bulb socket. No difference. No lights.
Everything worked when I last had the car inspected, but something obviously has deteriorated. Any additional thoughts?
Sounds like the Brown positive wire is bad from the rear connector to the lamp sockets.
I would guess, since I'm not there, it's bad at C320 or the splice to all the brown wires in the harness S360.
I would keep the C320 disconnected, a lamps OFF test, with an OHM-Meter from the brown wire in the C320 connector going to the lamps to the brown wire on each lamp socket. Should read a short on the meter from that pin on the connector housing the brown wire to the lamp socket brown.
You may need to open up the harness in the loom if it's an open circuit in the brown wire to find out why or snake a new wire in there back to the "good side" of the C320 connector brown wire you tested good power on.
I was thinking the same thing when I saw your post.
I actually tested that and didn't see anything I liked as results........I was going to post the results here, but instead started taking things apart to look at the harness, but then stopped as I had an epiphany....I recall that I stripped an '85 T-type (prior to 2000) and I thought I may have the original rear taillamp harness from it.
I rummaged around and actually found it (and its in much better condition that what I'm working with on the car now).
I'm thinking "easy fix, just swap".
I put some bulbs in it connected the C320 connector and G177 ground, turned on the switch and............. NOTHING.
Swapped bulbs, still nothing. Tested the bulbs; they're good.
Tested the power again and feed side of the C320 connector is indeed feeding 11.7 V with the switch on.
Disconnected the C320 connector and ran a jumper from the feed side of C320 connector brown wire to the receiving side of C320 connector brown wire and grounded the connector for G117.... still nothing.
(I'm basically bench-testing the taillamp harnesses at this point, no?)
Should I not be able to just feed the brown wire power from C320 to the harness and ground the connector for G117 and have the "parking/running lamps" light? What am I missing here?
Just to check my sanity, when the headlamp switch is in the parking lamp setting or the headlamp setting, in the rear taillamps, should not the small exterior lamps, the small middle lamps, the low brightness filament of both large lamps on each side, and the license plate lamp light? Brakes and turn signals engage the high brightness filaments in the center 2 large bulbs, yes? I'm looking at 8A-100-8.

Maybe the next test should be to hook up the '85 harness directly to battery voltage under the hood and ground and see if I can make it light that way. I was thinking that the brown wire on C320 was somehow compromised (amperage?) to not be able to light up lamps, but I tested that using the one bulb test you mentioned and I only had 1 or 2 bulbs in the '85 harness when I tested that.
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If you are going to use a test assembly you have to know it's good first. I'd try to get the lamps working as you mentioned with bat. power.
Everything out back lights up when the parking lights are ON as you mentione. However they are all powered on that one wire out of C320 and the one main ground point.
Good News, Bad News.
The '85 Rear Taillamp wiring harness seems to be different from the '87.
The wire colors on the receiving connector of S320 are different from the 87 which explains why I could not get the '85 harness to light. I was going by socket position and/or wire color.
I could possibly rearrange the pins in the connector, but there also does not seem to be an ancillary attached connector on the '85 like the '87 has.
So, going back to the original harness.....
I intermittently get 5.6-6.2V on the left outward small bulb (closest to the connector).
Again the connector inside the trunk is showing 11.6V.
With all of the bulbs removed except the small bulb in the middle of the LH taillamp, if I supply power to the positive side of the left-most small bulb connector (where I get 5.6-6.2V), the middle bulb lights....but if I put any large bulbs in, they do not.
I removed the outer protective socket cover of the LH large bulb and was greeted with a crumbling dried-out mess or what used to be some type of anti-corrosive sealant. I was expecting the contacts to be toast but they surprisingly were all bright silver in color. Supplying power to the socket connector itself, that bulb lights, but none of the other plugged-in ones do.
So basically, I believe I need to redo the harness on the positive side (maybe for each bulb socket?!?)....which is what I was hoping to avoid.
Will keep you posted.
Does anyone know what material (grease?) was originally used (or could be used) inside of the two halves of the plastic bulb sockets for the larger bulbs??? (This is not where the bulb goes in, but rather INSIDE of the plastic socket halves which can be separated). When the original material came out, it was a yellowish almost wax-like substance (but powdery & dried out).