Courtesy light short

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orthodoc
Posts: 37
Joined: Mon Aug 10, 2015 9:08 pm

Courtesy light short

Post by orthodoc » Wed Aug 08, 2018 12:30 pm

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?
1963 Thunderbird Roadster Convertible
"Rangoon Red"

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MN63Tbird
Posts: 145
Joined: Mon Nov 02, 2015 12:38 am
Location: Minnesota

Re: Courtesy light short

Post by MN63Tbird » Thu Aug 09, 2018 5:00 pm

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
1963 Thunderbird Hardtop
1966 Mustang Coupe A code

orthodoc
Posts: 37
Joined: Mon Aug 10, 2015 9:08 pm

Re: Courtesy light short

Post by orthodoc » Fri Aug 10, 2018 1:58 pm

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.
1963 Thunderbird Roadster Convertible
"Rangoon Red"

User avatar
MN63Tbird
Posts: 145
Joined: Mon Nov 02, 2015 12:38 am
Location: Minnesota

Re: Courtesy light short

Post by MN63Tbird » Sun Aug 12, 2018 9:42 pm

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
1963 Thunderbird Hardtop
1966 Mustang Coupe A code

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