98 Camry: Procedure to find root cause of blown tail-light fuse

Question

Question: What are the steps and thought process to determine why excessive current has blown the tail-light fuse?

Symptom: night running lights failed to illuminate when engaging headlights.

Problem: Fuse 28 was blown. Replacing the fuse seems to have (at least temporarily) solved the problem.

Factoid Wondering if the root cause has something to do with the unusual high blinking-rate of the left turn signal.

List of fuses found in instrument panel:

After fuse replacement, night running lights are functioning:

I would like to understand why the fuse blew and fix the root cause of the problem.

Wiring to the trunk lid is normally strapped to the hinge arm and then passes inside the lid channels to each light. When you combine the trunk slamming with sharp metal edges, wires can easily be nicked and cause a short. — John Canon, Jul 3, 2021 at 23:23

Solar Mike · Accepted Answer · 2021-07-02 04:13:11Z

1

Find the short - could be a faulty bulb, could be a screw hitting the wire, could be a sharp metal edge.

Use a meter or even replace the fuse with a bulb - if the bulb is lit the short exists.

Work from one end to the other checking very carefully - even the tiniest hole in the insulation could be the culprit.

answered Jul 2, 2021 at 4:13

Solar Mike

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Thank you for the helpful guidance. I think you are suggesting to measure the current (replace the fuse with an ammeter) with the headlights off. The current should be zero. If there is any current is not zero, then there is a short?
– gatorback
Jul 2, 2021 at 12:49
@gatorback if you replace the fuse with an ammeter, then you will find the short very quickly as there will be massive current flowing... I suggested replacing the fuse with a bulb as it is a resistance which limits the current and won’t cause any damage - unless you use a 1000W bulb . I suggest a 5W would be suitable. A method I used often as a vehicle electrician but you do as you see fit.
– Solar Mike
Jul 2, 2021 at 12:53

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