Courtesy light short

[orthodoc]

I have an apparent short in the circuit for my courtesy/interior lights on my 63. Every couple of days the fuse will blow. I've tried disconnecting the map light, as I've heard others have had a short in the switch there, but still no success. Does any one have any tricks/ what is the most efficient way to track down such a short?

[MN63Tbird]

I had posted in the power seat post a few items you need that will be able to resolve electrical wiring problems. You need to get the following:

1. Wiring diagram- primary need is to find what is the wiring route but most important is identifying the wire colors
2. About 20-30 ft of #18 gauge or larger insulated wire with alligator clips attached to each end.
3. Volt meter with an acoustic continuity setting so you can hear when you have continuity across two wire ends. Easier than reading the meter.

Total cost should be less than $35

Your light circuit includes the map light, the dome light, side door lights and the 2 light switches. The map light housing and the dome light housing as they attach to the car provide the ground. The side door lights have one black wire that should be attached at some point to the car body to provide a ground. They all should have a black blue wire running to the switches for power.

If you keep blowing fuses the first check is do you have the right fuse. It should be 14 amps. Note the 7.5 amp fuses will also fit into the same location by mistake. If the fuse is correct then the next checks are the bulbs for the lights. Are they the right size? Are the sockets clean and not damaged or rusted?

Are the grounds all clean where the map light and dome housing attaches to the body. This will involve removing the map light and dome light which are held on by a couple screws. The side courtesy lights are a little more of a pain since you need to remove the door panel. This involves removing all the screws around the door and popping off the door handle. There is a special tool to remove the clip on the door handle but I use an awl with a bent end to reach under the clip and pull it off. Check the door lights and door wire ground with the panel off. There should be a black 2 pin connector inside the door that can be disconnected to pull the door panel away and check the light sockets easier.

If the sockets and grounds are good then then next step is to work down the wiring for each to ensure continuity. You can start by removing the fuse and then opening the doors. Attach one clip to the fuse end and the other clip to your volt meter. Starting at the Map light, attach the other lead on your volt meter to the wire going to the fuse from the map light housing. Set the voltmeter to acoustic continuity and listen for a beep. If you hear a beep then the wire between the is good. Close one door and depress the light switch. The beep should stop. If it is not a clean cutoff then there may be an issue with the switch. Repeat with the other switch. Disconnect the clip at the fuse and connect the clip to a good ground on the body. If you hear a beep also on that try then that is not good. The wire complete the circuit but is exposed and grounded to the car somewhere. That could be your short. You will also see some ohm reading on your meter if there is a short. Repeat the same technique with each light bulb. You do not need to repeat the switch checkout if you are satisfied with the first try. If you find a bad wire you will need to replace that wire in the circuit.

The process sounds a bit involved but you will learn a lot about your car in the process.

My experience with different cars is that the short is usually a bad or corroded light bulb socket or the wrong fuse.

Good Luck

MN63

[orthodoc]

Thanks, great advice. I hadn't thought about the door switches, they could certainly be a culprit. I could be wrong but I think the service manual has that circuit listed as a 7.5A fuse.

[MN63Tbird]

Otrhodoc

I just rechecked and my 63 wiring diagram says 14 amp fuse. The 62/63 shop manual on sec 10-7 says 15 amp for the 62. Your fuse size may be the issue.

MN63

[Gagarin]

Reviving this topic but adding a twist. Hoping one of the more experienced on here may have some advice. I recently replaced the dash and interior on my 63. Remarkably I ended up with a small list of punch list items but one which baffles me is the courtesy lights will not shut off when closing the doors. It gets even better, I pulled the fuse for the circuit and they are still on? oops?

I have all of the schematics electrical build sheets etc. I am completely baffled? Any suggestions from others which may have gone down this road?

[MN63Tbird]

I like the electrical challenges. With the light on and the fused pulled there can be only 3 causes. First is that you may have pulled the wrong Fuse. The Courtesy light fuse should be the 3rd socket down on the left side of the fuse panel (the first socket may be empty). Double check that is the correct fuse that you pulled.

The second is if the correct fuse is indeed pulled then the only way to get power to the lights is for the circuit to be wired to a wrong fuse or circuit breaker. If that is the case then follow the steps in my previous post. Check for continuity between the courtesy light and each fuse and circuit breaker on the panel with the Passenger door open. I would suggest disconnecting the battery so you do not accidentally short out something. Once you find continuity you have found where your lights are wired to. If the lights are wired to an incorrect fuse or circuit breaker then they are bypassing the switches and will stay on all the time.

The final cause can be one or both bad switches. The switches break the circuit stopping electricity from going to the lights but if either one is not working then the lights will stay on. One or both switches may be shorted. This can easily occur over 57 yrs of weather. If you can check continuity across each switch then you can check if they are working. Depressing the switch should break the circuit.

If the switch is working and hooked up to the correct fuse but the lights are not then you need to rewire the lights. This is where your wiring diagram can come in handy to follow the color codes of each wire. You will need to pull the panel off around the fuse panel to see all the wires and which is going where and pull off the passenger door panel to confirm the correct colored wires are leaving the courtesy light. This is a bit more work but just a matter of making sure the right colored wire goes to the correct location.

MN63

[Gagarin]

MN 63,
Looks painful but understand that it is a learning curve and I am going to be an expert and ready for the next project at the end of this. I have all of the instruments / materials on your list so off I go. It is hard to nail down cause and effect when you have replaced the dash and when you get it all back together you have another issue but I had a short in the map light before so I just need to dig into it.

Thanks again, I will report back.

[Gagarin]

So, I sat in the passenger seat pulling wires and checking them against my schematic. I did not have the map light wired up so I hooked that up to complete the circuit and then blew the fuse! Ran out of time and patience (and fuses) but I am back to it this AM. I am kicking myself for not installing a new harness whilst I had it apart. I have a few PO issues as well where you can see that something has been altered, this only complicates things.

I shall soldier on....

[MN63Tbird]

Good luck on working around the fuse box. Its not as difficult as working under the dash on the drivers side but there is no real comfortable position to put your self into to work on it unless you really want to get adventurous and take out the passenger seat.

With the kick panel off and the door panel off you should get a good idea of where the wires go. The map light is a bit of a curiosity. It does not draw that much amps and should not blow a 14 amp fuse. I was wondering if that is being shorted out somewhere along the line. You can pop that out by removing the 4 screws. The light should have a quick disconnect on it that is visible with the cover off. To see if it is shorting to the car pull the fuse, pull the disconnect apart and then put one end of you ohm meter into the wire that goes back to the fuse box and the other on a metal part of the car that is grounded. If you get continuity that wire is being grounded some where. Fortunately it is easy to feed a new wire back over to the fuse box if that is the case. There is access along the way over the heater to the kick panel. If you do not find a short there then check inside the light socket. I believe the outer casing goes to ground and the center goes to power. There should not be any corrosion that creates a short. Good Luck

MN63

[Gagarin]

First off, I just finished a 7 mo. reclaim of the interior so I feel like I have a zipper on those seats, I am 6'3'' with bi-focals,I have no room to get in there and cannot get in a good position to see the detail, I already pulled it. :-)

Excellent additional advice. In working through this issue, based on your helpful advice, I have corrected other issues but I am back to the real issue today. I did replace light switches for the doors yesterday as I wanted to eliminate any other maybes? I like the re-wire option. Thanks again!

[Gagarin]

Sorry to go long on this but I always like to pass on lessons learned. First off, thanks to MN63Tbird, and you were right, you certainly learn the car checking for continuity! I certainly appreciate the detail you provided.

I replaced the door switches without even checking them, I replace with new wherever I can and then I started checking continuity of which I was a complete neophyte prior but after a couple of tutorials on YouTube I was up to speed. Lucky for me I did not need to go very far as there was an issue with the map light, the actual bulb or the socket was the issue? I pulled the bulb and the problem was solved. I need to find a new holder etc for the map light.

I was off and running this afternoon, getting the radio back in and replacing the kick panels. Life is good. I took it for a short drive this afternoon and remembered what all my hard work was about. It really has turned into a driver.

[MN63Tbird]

Gagarin, Glad to hear you were successful in solving the electrical problems! Also happy that I could be of assistance. For most of my electrical issues I do the continuity check to find out where my wires are going or not. Unintentional grounds or wires that were routed to the wrong location are the source of most the electrical challenges. During the winter months I restore old tube radios from the 30s to 50s. Find similar issues there too.

Happy Driving.

MN63