Q I have an old high-mileage ’95 SUV. The rear indicator-signal lights have started flashing very rapidly. I always thought this was caused by a burned-out bulb, but both the front and rear lights are flashing quickly. How do I fix this?
A Start by looking at the widget that makes the signals actually blink, the thermal flasher, aka the indicator-signal relay. For most of its history, the relay has remained largely unchanged. It works by passing current through a thermal element that heats up, expands and closes a connection between the 12-volt power source and the bulb, sending power to the signal light. The thermal element then cools and contracts because the current isn’t passing through it, opening the circuit and turning off the light. The most likely cause of your rapid flashing is that the relay has worn out and the springs it rests on have lost their bounce.
Fixing the problem is easy and cheap. Head to your local spare parts store and ask for an indicator-signal relay for your vehicle. They’ll hand you a small, round, metal part that looks a bit like a little stockpot turned upside down. Root around in your fuse panel to locate the matching part and replace it – your owner’s manual or the lid of the fuse-box cover will help you find where this part is hiding. Most of the time, the replacement part looks almost identical to the original. Switching the parts is as easy as pulling the old one out and popping the new one in.