Inop license plate lamps - tip of the iceberg
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Inop license plate lamps - tip of the iceberg in Past Cadillac Vehicle Discussion; I noticed that both of my license plate lamps are out. It's unlikely they were both bad, but I replaced ...
  1. #1
    EcSTSatic's Avatar
    EcSTSatic is offline Cadillac Owners Connoisseur
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    Inop license plate lamps - tip of the iceberg

    I noticed that both of my license plate lamps are out. It's unlikely they were both bad, but I replaced both bulbs and no change. I opened up the service manual and there is a section on them. Actually, the lamps are tied in with the cornering lamps and under hood lamp. The manual says if all are out, check fuse DIMR in the rear fuse block. Well none of them work, but the fuse is fine. I even swapped a known good one and still no change. The next step in the troubleshooting section says to replace the fuse block! Evidently that's the distribution point for all these circuits.
    Has anyone been down this road before? I'm guessing that a new fuse block ain't cheap. I'd leave it alone except you can get a ticket for inop license plate lighting. i can remove the block and look for corrosion, but it's a pretty protected area. Any thoughts?

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    JimD is offline Cadillac Owners Connoisseur
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    Re: Inop license plate lamps - tip of the iceberg

    Quote Originally Posted by EcSTSatic View Post
    I noticed that both of my license plate lamps are out. It's unlikely they were both bad, but I replaced both bulbs and no change....

    ....check fuse DIMR in the rear fuse block. Well none of them work, but the fuse is fine. I even swapped a known good one and still no change. The next step in the troubleshooting section says to replace the fuse block!
    Whoever wrote the troubleshooting section flat out ignored the relay in the circuit.

    As a test, swap the PRK LP relay (underseat fuse box) with a known good relay as a test.

  4. #3
    satlite440 is offline Cadillac Owners Member
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    Re: Inop license plate lamps - tip of the iceberg

    do you know how to use a test lamp? ck and see it the lamp houseing/sockets are getting power. also the penut rubber sockets tend to melt over the contacts for penut bulbs.. the newer penut/blue socket types need to often be replaced together

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    EcSTSatic's Avatar
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    Re: Inop license plate lamps - tip of the iceberg

    I didn't see the relay in the diagram, but I'll take another look. There's a PK LP 10A fuse in the circuit but it is good. It makes sense that there is something else that controls the lighting. Something in front of the fuse.

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    JimD is offline Cadillac Owners Connoisseur
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    Re: Inop license plate lamps - tip of the iceberg

    Quote Originally Posted by EcSTSatic View Post
    I didn't see the relay in the diagram....
    The PRK LP relay contacts are not shown in the License, Underhood and Cornering Lamps diagram. But there is a reference to the relay ("G") to indicate where the DIMR fuse receives voltage.

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    EcSTSatic's Avatar
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    Re: Inop license plate lamps - tip of the iceberg

    Found the relay, swapped it with a good one. Now the cornering lamps and the under hood lights work but the license lamps still don't. <sigh> I'll look at it some more tomorrow. Thanks for the tip, I'm 2/3 of the way there!

  8. #7
    JimD is offline Cadillac Owners Connoisseur
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    Re: Inop license plate lamps - tip of the iceberg

    Quote Originally Posted by EcSTSatic View Post
    Found the relay, swapped it with a good one. Now the cornering lamps and the under hood lights work but the license lamps still don't. <sigh> I'll look at it some more tomorrow. Thanks for the tip, I'm 2/3 of the way there!
    Your next step(s) should include a test for a broken chassis ground wire between the plate bulbs wire harness (black wire) and the chassis ground location at the LR corner of the trunk. Use a piece of wire as a redundant ground.

  9. #8
    accuab's Avatar
    accuab is offline Cadillac Owners Member
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    All the lights were out on the trunk except the third brake light when I got mine. I grounded the harness out with a spare wire a and it worked. I traced the ground wire at the back left of the trunk and found the ground wire had broken from the tension of the trunk coming to a stop when opening. I spliced in a 6 in extension to avoid it pulling anymore and and have had no other problems with it. You can test for power at the connector with a dmm. Put the ground probe on a metal point of the body and probe the connections with the positive to make sure voltage is there. Since you have the manual you may be able to look up which pin is the tag lights and specifically probe them.

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    EcSTSatic's Avatar
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    Re: Inop license plate lamps - tip of the iceberg

    It's fixed! Just as you said, tension at the trunk lid hinge broke the ground wire. I spliced it, taped the bundle which was uncovered, and worked the clamps so that everything seemed to have enough play.
    I had two problems; the bad relay which controlled the hood lamp, cornering lights and license lamps, and the broken wire that provides a return for the license lamps. It's all back together and working now. Thanks everyone!
    Moral of the story; don't take your shop manual troubleshooting steps as gospel.

  11. #10
    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a sound system
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    Re: Inop license plate lamps - tip of the iceberg

    Quote Originally Posted by EcSTSatic View Post
    the bad relay which controlled the hood lamp
    Is the 1999 in the vehicle series that has the underhood light that is supposed to operate only when the parking lights are on ?

  12. #11
    JimD is offline Cadillac Owners Connoisseur
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    Re: Inop license plate lamps - tip of the iceberg

    Yes. 1998 to 2002 Sevilles. Schematics for 2003 and 2004 do not show an underhood light.

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