Keep blowing rear taillight fuse
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drfaktor
- Posts: 2
- Joined: Mon Jan 21, 2019 6:32 pm
- Your car is a: 81 spider 2000
Keep blowing rear taillight fuse
I have an 81 spider and noticed the rear drivers side taillight is out. Cleaned the circuit board and still out. Noticed it blew a fuse so I changed it and now it just keeps blowing the fuse immediately. Any idea where to start?????
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18Fiatsandcounting
- Posts: 3799
- Joined: Fri Mar 15, 2019 11:23 pm
- Your car is a: 1969 and 1971 124 spiders
- Location: San Francisco Bay Area
Re: Keep blowing rear taillight fuse
This definitely sounds like an electrical short somewhere. A few questions: The issue is the taillight and not the brake lights, correct? Are the passenger side taillight, all side marker lights, and front marker lights working as they should? Is the fuse the correct value?
-Bryan
-Bryan
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aj81spider
- Patron 2020
- Posts: 1526
- Joined: Fri Mar 11, 2011 9:04 am
- Your car is a: 1974 Fiat 124 Spider
- Location: Chelmsford, MA
Re: Keep blowing rear taillight fuse
Sounds like you have a short. To find it you need to disconnect parts of the circuit until you find the part where the short is, then you can fix it. If it is the tail lights and not the brake lights then you can approach it like this:
> Does the fuse blow with the lights off or only when they are on?
- If it blows when they are off then the problem is not in the light or the wires going to the light - it is in the wires going to the switch or in the switch itself.
- If it blows when they are on then I would first disconnect the tail light - it's more likely to be in that then in the wires unless you did something to cut a wire and cause a short.
You can use a meter (it's cheaper than fuses, and can be done with power off!) to measure the resistance of each part of the circuit. The part with 0 resistance is the part with the short - at that point you just have to find it visually.
Make sure you disconnect the battery.
Start by measuring at the fuse terminals. They should measure close to 0 ohms if the fuse is blowing. Then as you disconnect different parts of the circuit you can continue to measure there until the resistance goes up. When the resistance goes up you know the short is after the connection you just disconnected.
A wiring diagram will help you determine where there are connectors that are easy to disconnect.
> Does the fuse blow with the lights off or only when they are on?
- If it blows when they are off then the problem is not in the light or the wires going to the light - it is in the wires going to the switch or in the switch itself.
- If it blows when they are on then I would first disconnect the tail light - it's more likely to be in that then in the wires unless you did something to cut a wire and cause a short.
You can use a meter (it's cheaper than fuses, and can be done with power off!) to measure the resistance of each part of the circuit. The part with 0 resistance is the part with the short - at that point you just have to find it visually.
Make sure you disconnect the battery.
Start by measuring at the fuse terminals. They should measure close to 0 ohms if the fuse is blowing. Then as you disconnect different parts of the circuit you can continue to measure there until the resistance goes up. When the resistance goes up you know the short is after the connection you just disconnected.
A wiring diagram will help you determine where there are connectors that are easy to disconnect.
A.J.
1974 Fiat 124 Spider
2006 Corvette
1981 Spider 2000 (sold 2013 - never should have sold that car)
1974 Fiat 124 Spider
2006 Corvette
1981 Spider 2000 (sold 2013 - never should have sold that car)
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drfaktor
- Posts: 2
- Joined: Mon Jan 21, 2019 6:32 pm
- Your car is a: 81 spider 2000
Re: Keep blowing rear taillight fuse
Thanks. I’ll give it a try. I did put in new seats and carpet so I could have clipped a wire since it runs by the drivers side seat
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spider2081
- Patron 2024
- Posts: 3015
- Joined: Fri Jan 27, 2006 11:45 pm
- Your car is a: 1981 Spider 2000
- Location: Wallingford,CT
Re: Keep blowing rear taillight fuse
IF you don't have a wire diagram I suggest you join the chat room Mirafiori.com access their library and download the 1980-81 Spider diagnostic manual.
Light circuits shorts are very difficult to troubleshoot using an ohm meter. The resistance of a single light bulb is pretty low. When tracing light wires with an ohm meter you will be measuring the resistance of many bulbs in parallel so the resistance becomes much lower to the point it appears as a short. I think disconnecting branches to isolate the short can be more effective.
Fuses 7 and 8 protect light circuits in the Spider. Fuse 7 is left tail right front parking and left rear marker light. Fuse 8 is right tail, left front and right rear marker light. It is also the dash lights, trunk light and the lights on indicator in the speedometer.
Most common intermittent shorts in the Fuse 8 circuit are the trunk light wire and the right marker plate wire. I would physically inspect their routing and connections.
Light circuits shorts are very difficult to troubleshoot using an ohm meter. The resistance of a single light bulb is pretty low. When tracing light wires with an ohm meter you will be measuring the resistance of many bulbs in parallel so the resistance becomes much lower to the point it appears as a short. I think disconnecting branches to isolate the short can be more effective.
Fuses 7 and 8 protect light circuits in the Spider. Fuse 7 is left tail right front parking and left rear marker light. Fuse 8 is right tail, left front and right rear marker light. It is also the dash lights, trunk light and the lights on indicator in the speedometer.
Most common intermittent shorts in the Fuse 8 circuit are the trunk light wire and the right marker plate wire. I would physically inspect their routing and connections.