Number plate lights not working

I would bet it is a grounding problem. Test the bulb with a resistance meter, if ok remove the fixture and clean the grounding contacts as the light won't work if the fixture isn't grounding to the car, if that doesn't correct it check the fuse.

 

Of course, check the fuses first -- fuse #15.

 

The light fixture is located under the lip of the engine bonnet over the license plate

 

here is what the fixture looks like. Remove the two screws, clean then along with the metal portion of the fixture that touches the engine bonnet, check the bulb and hopefully it work on install
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Should the battery be disconnected while this work is being performed?

 

Yes, I recommend disconnecting it anytime you are working on electrical parts lest you might blow the fuse if it is not already blown. Your car should have a quick disconnect on the drivers side front boot of the car near the radiator fan...a red connector most likely.

 

I should add that my experience is quoted based on a 1986 US GTB...a 308 Euro could be different but I doubt it...other 308 owners could confirm.

 

I also have an '86 328 GTB; I don't think there's a quick disconnect...

 

That's what I thought until I looked at the owner's manual...there is one there ok...it's a big red clip with a large flat copper wire coming out of the radiator side...just pull them apart...it's definitely there and it's a while lot better than disconnecting the battery each time!

 

here you go, a pic from a service manual (search this site for "disconnect" to find the original thred I started on this)...part #25 and #26 are red in color and pull easily apart. But I should add that on a 328 the battery and disconnect are in the front boot and NOT in the back with the enging! A 308 owner chimed in on that thred to indicate that his car had the same disconnect.
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Measure the voltage at the top and bottom terminals (where the wires are attached) of the fuse using the same device that you used to determine that you had no power on the wire at the rear bonnent -- when the exterior parking lights are "on", you should have power present at both the top and bottom terminal of that fuse position.

 

Using a resistance meter test the fuse as noted in the previous message. Sometimes they appear to be good but are not. If the fuse is good then check the bulb, again using a resistance meter. If the bulb is good let's test the black and yellow wire in your photo to see if it has current. To do that turn your rear driving lights on. First, do the tail lights work? If so, you at least have power to the rear of the car. If so it's time to check to see if you have current in the black and yellow line in your picture. Unplug the plastic connection in your picture - the connection is solely to make it more convenient for engine services that require that the engine bonnet be removed. Check the front side of the connection (side closest to the passenger compartment) using a voltage meter and grounding it first to a ground connection point in the engine compartment and if that is ok then the ground connection where the light fixture screws into the engine bonnet. If those are good then reconnect the plastic connector and do the same testing the wire from the end point where it connects to the light. The black and yellow wire in your picture is supposed to bring positive current to the light fixture when the tail lights are turned on and the fixture is grounded to the body via the screws that hold the fixture in place. My car has a grounding problem and the connector (the one in your picture) was also loose.

 

The negative wire from those lights are probably connected to the negative wires from the backlights and stoplights. Those are the black wires who comes togheter between stop and directionlights inside the backbooth. With a simple screw those wires are connected to shell. Clean them and put some coppergrease.
Guido

 

Checked last night; its there. Been staring at it for 6 years without really knowing what it was!

 

It was mentioned that there is no power at the conncetor on the hood (in the photo). You could have the best ground in the world at the lamp fixture but it's not going to light up if you don't have 12 volts even getting to the connector.

 

I think you're going to have to trace the wire back from the engine cover into the cockpit or towards the rear lights (depending on how it's routed) and then towards the fuse panel. Hopefully you'll hit a multi wire connector somewhere that just needs to be taken apart, sprayed with some contact cleaner and re-connected. Still...... doesn't sound like fun.

I assume when you checked for 12 volts at the connector you put the voltmeter's ground lead on a good, clean, unpainted metal surface. Otherwise the results of your check may have not been valid.

 

The schematic in the back of the euro 308QV OM shows that the +12V GN (yellow/black) wire going to the number plate lamps comes from the RH rear (red) parking light --

Does your RH rear (red) parking light come "on" OK?

Check the GN wires at the RH rear parking light socket -- they are swagged into a common female spade terminal (which is supposed to connect them electrically).

 

hurray! Best of luck!