An opportunity to buy a new diagnostic tool: this time, a "short tester".

Dear Car Talk

Dear Car Talk | Jun 01, 1999

Dear Tom and Ray:

I just bought a 1988 Ford Escort Wagon for my wife, and I found out the brake
lights don't work. The fuse was burned out. When I replaced it, it took just a
pump or two on the brakes to blow the fuse again. I did this three or four times
(duh!) and finally replaced the rear bulbs. Then I replaced a faulty engine
ground strap, and I still have the problem. I think I have a dead short, but I
have no idea how to go about finding it. I would sure appreciate any help you
could provide. -- Mark

RAY: Well, Mark, my first piece of advice is to look at every car problem as an
opportunity to buy a new tool. And the tool you need this time is a "short

TOM: Whenever I buy a new pair of BVDs, there's a little tag that says "inspected
by No. 19." Wouldn't that make No. 19 a short tester?

RAY: No. The short tester Mark needs is available for about $20 at any good auto
parts store. It's a self-resetting circuit breaker, which you insert in place of
the fuse. So when you step on the brake pedal the circuit breaker will blow, and
then -- when it's cool enough -- reset itself. And it'll do this indefinitely,
which will save you from having to tap your 401(K) to pay for fuses.

TOM: The other piece of the short tester is a very sensitive induction ammeter.
So you have an assistant plant his or her foot on the brake pedal, and then you
move the ammeter slowly around the outside of the car. And when you get to a
place where the needle is swinging wildly back and forth, that's where the short

RAY: If you don't want to go through this search, you can save time by simply
asking the previous owner where the accident was. I'd be willing to bet that
somewhere along the line, this car was hit in one of the rear quarter panels, and
a brake light wire got pinched, and now it's shorting out.

TOM: Of course, that eliminates the excuse to buy a new tool, Mark. So forget
that my brother ever said that.

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