Dome light question

[waltmail]

Just got a very nice dome light from Jim Finn. I know it is a good unit. Tested from battery source. MY question is what controls the dome light? Isn't it a timer. Putting a voltmeter on the circuit at the bulb contacts does not indicate a drop off of the voltage after the 20 seconds has elapsed. What gives?

[Ronnie]

The light always has 12 volts. The light is controlled by the BCM and the courtesy light relay on the ground side of the circuit.

[waltmail]

The light always has 12 volts. The light is controlled by the BCM and the courtesy light relay on the ground side of the circuit.

So what turns it on? Is this a photocell function?

[KDirk]

The dome light is controlled (indirectly) by the door jamb switches. When a door is open (switch closed), the switch signals the BCM to apply ground to the courtesy lamp circuit - both the dome and footwell lamps as well as the marker lamps on the door panels - as Ronnie stated. The same circuit is also enabled when the interior lights slider on the headlamp switch is slid all the way to the right (past the detent) to force the interior lights on.

In the interest of being thorough, the map lights on the rearview mirror are also tied to the courtesy lamp circuit in early production 88 models. This feature was omitted sometime after build 1134 (which is one of my cars and does have this feature).

If your other interior courtesy lights are working (one in each footwell and the red/white door panel marker lights) then the issue is the socket, bulb or wiring for the dome lamp. If none are working then troubleshooting the courtesy lamp circuit is in order.

KDirk

Edited May 6, 2015 by KDirk (see edit history)

[waltmail]

If none are working then troubleshooting the courtesy lamp circuit is in order.

KDirk

Still looking for this at ROJ. I found a write up b Padgett, Barney and McReatta. Don't know if one or all apply. Before I go any further I should mention that my headliner, visors, door cards and all connections are out of the circuit.

[Barney Eaton]

On your 89, the first thing the ground side goes to is the interior relay "C", then to ground.

You could have a bad relay or the BCM is not grounding the grey/black wire that goes to the relay coil

You will find the relay in the right front of the console.

Said in another way... the BCM grounds the grey/black wire when certain conditions happen (door is open, you turn on the dome light, etc) the grey/black wire goes to the pick coil side of the relay, the other side is

hot (orange wire going to body fuse 2) if there is no power on the orange wire, then the relay will not pick and ground the dome light wire.

Also note that the footwell courtesy lights and R & L door courtesy lights are on the same circuit as the dome light, the footwell lights are connected thru splice S305 under the passanger seat and this is a known problem but the dome light splice is S214 behind the IP and usually not a problem.