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One or more rear lights does not work. Or you get annoying
messages telling you that one or more light bulbs are broken
(but they actually work just fine).
Tools, Skills And Parts
The job is very easy to perform and does not require any kind of special tools.
The following tools are required for this particular work (tools marked with green checkmark are optional).
The following spare parts are required for this particular work (parts marked with green checkmark are optional). Note that the BMW internal numbers are intended for a BMW 535i E34 -89.
The rear light bulbs are easily accessed from the trunk. Simply remove the rear-panel trim after opening the quick-release fasteners. In Picture 1 you can see the location of all the different rear lights are. Further down I have also listed what type of light bulb that are used in the different rear lights.
Picture 1 : The location of the different rear lights.
Only two different type of light bulbs are used at the rear, the so called P21W BA15s and the R5W/R10W BA15s light bulbs.
The P21W and R5W/R10W notations defines in which category (in the european ECE R37 and american SAE regulations) the light bulb belongs in. The first letter defines the shape or type of the light bulb. It is followed by the power rating (in Watt) of the light bulb.
Take the P21W for example, the letter P says it has a pear shape and a rating of 21 W. Below you can see a list of the most common shapes.
Sometimes you can come across a light bulb called P21/5W. It's actually two light bulbs in one (it has one one extra filament and contact point compared to an ordinary light bulb).
Picture 2 : Picture of the most common light bulb shapes.
Picture 3 : To the left a P21W bulb and to the right a R5W bulb.
Picture 4 : A W5W bulb.
The second expression, BA15s, defines the socket type. All light bulbs at the rear has the so called BA15s socket. The P21/5W ligh bulb mentioned earlier often uses the so called BAY15d socket. It differs from the BA15s by having two contact points at the bottom but also the bayonet pins are slightly offset. In Picture 5 and 6 you can see how the BA15s and the BAY15d sockets looks like.
Picture 5 : A BA15s socket.
Picture 6 : A BAY15d socket.