Car Talk

July 2005

Dear Tom and Ray:

I have run into a problem with my 1993 Jeep Cherokee Sport. Something
is causing the fuse that serves the power door locks, radio, cigar
lighter and dome light to blow. You put in a new fuse, and it blows
before you can even test things out. Just before this started, the
power locks were acting up -- sometimes they would work, and
sometimes not. Could the power-lock switch or actuators cause this?
Is it going to be a matter of replacing the locks, or can this be
fixed without buying an all-new set? I would really appreciate any
help you can throw my way. -- Matt

Beat up old car

TOM: This is going to be a pain in the butt, Matt. Fortunately, at
least you've got a good type of short to deal with.

RAY: Right. You've got a dead short, which means it's not
intermittent -- it blows the fuse immediately, each and every time
you replace it. That makes it easier to find than, say, a fuse that
only blows once every three weeks when the moon is in the southern
sky, and Maura Tierney cracks a smile on "ER."

TOM: The way to find a dead short is, first, buy a buttload of
replacement fuses. Then start disconnecting one suspected electrical
component at a time. After you've disconnected a component, replace
the fuse. If it DOESN'T blow, you've hit pay dirt.

RAY: Approach it logically. You know it's either the locks, the
radio, the lighter or the dome light. I'd start by eliminating the
radio. Radios almost never blow fuses, in my experience. So now
you're down to three possibilities. That was easy, right?

TOM: I'd disconnect the lighter next. You can remove the wire from
the back. That's easy to do, and lighters frequently cause problems.

RAY: When that's not it, Matt, go for the dome light next. That pulls
down from the headliner. Once it's pulled down, the wires should be
exposed. That's easy, too.

TOM: And when you've eliminated everything else, you then have to
tackle the door locks. That's not so easy.

RAY: Well, it depends. Start by opening the door and looking at the
area where the hinges are. You'll see a sheaf of wires that exit the
A-Pillar (the front of the door frame) and enter the door itself.
Since those wires get bent every time the driver's door opens and
closes, that's where you're most likely to get a fraying or broken
wire that's touching metal or touching another broken wire. So, look
there first and see if you can find any evidence of exposed wiring.
If you do, fix it, and then test it.

TOM: If you don't find a problem there, then you're going to have to
remove the inside door panel. It's held on by about 1,400 little
clips. Try not to lose more than 1,300 of them, or it'll be hard to
get the door panel back on.

RAY: You can then try disconnecting the door-lock switch. If the fuse
still blows, try the actuator itself. Once you get that fuse to not
blow, you're in business, Matt. Good luck.

Back to the July 2005 index

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