[elkyD68]

I have a short somewhere in my instument lights or tail lights and keep blowing the fuse. What is the best way to find this particular short?

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Derek TC Member #1645
68 El Camino
Free cookies to anybody that can get my gas mileage over 20.

 

[LouieHammel]

Derek, I have a little buzzer that I put in place of the blown fuse. You can hear the buzzer 'buzz' continuously from anywhere around the car as long as there is a short to ground somewhere in that circuit. Start wiggling, yanking, and poking all the associated wiring until you hear the buzzer stop or become intermittent. When it does, you have found the location of the shorted wire.

Good luck,

Louie Hammel

 

[John_Muha]

Which fuse keeps blowing? If it is not the short instrument light fuse, it's probably not the instrument lights. Though it could be somewhere between the headlight switch and the fuseblock. If it's not the instrument light fuse (bottom center), a couple of things to try. Pull the instrument light fuse and see if the input fuse blows. Disconnect the front turn signal lamps from harness. There's connectors under the car. See if that stops the fuse problem. Sort of a process of elimination.

 

[elkyD68]

Thanks for the tips. I had forgotten that the instument lights were on the smaller fuse, I had just assumed that it could be part of the problem since they went out when the fuse blew. I recently replaced my headlight switch and I'm wondering if it could be part of the problem. How can I test it?

 

[John_Muha]

I won't assume it's a switch problem if the fuse blows when you turn the switch on. More than likely to be something after the switch. Louie's suggestion was a good one if you have the right tools. Otherwise it's hunt and dig. Here's the switch wiring if you need it.
Red is the input 12 volts for the headlights.
Pull the switch on puts power on the blue wire.
Blue is the output wire from the switch to the headlights.
Orange is a fused power input 12 volts for the dashlights and taillights.
Pull the switch on and it powers green and brown.
Green goes to dash lights
Brown goes to taillights.

 

[cjlandry]

Unplug the switch and check the wires through the plug with an ohm-meter. If you don't have one, you can pick up a cheap one at any parts store or even Wal Mart for around $5. Make sure it has batteries or the ohms readings won't work.

Set it on ohms and check each wire to chassis ground. They'll all give you a reading because you're reading through the bulb filaments. However, the lowest reading (nearest to zero ohms) will be your short circuit.

Be aware, though, if you're not familiar with analog ohm meters, that the needle needs to be "zeroed" by holding the two probe tips together and setting it with the knob. Also, the lowest reading in ohms will be the reading that moves the needle the farthest to the right (you probably noticed this when you zeroed the needle).

Once you determine which wire is shorted, use John's color info above to tell you where the wire is going.

BTW, give me the specs of your car and I'll tell you how to get the mileage above 20mpg. I want those free cookies.

Mine gets 21-22 mpg on the highway with 3.55 gears and it ain't slow.

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My Web Page (updated 06-21-02)

"Long Live Freedom!"

Chad Landry
TC Member #643
ACES Member #4556
'68 El Camino

[This message has been edited by cjlandry (edited 10-02-2002).]

 

[John_Muha]

Chad's method works but sometimes it's easier if you remove the running/tail light bulbs first. Yep, you can do it with the bulbs in but it's a little harder with a cheap meter. It gets easier to do the 3rd or 4th time you chase something like this, but I hope this it your last time on this car.

 

[cjlandry]

Doh! Removing the bulbs would be much easier.

I use a Fluke 87-III. Not a cheapo.

 

[elkyD68]

I'll start checking the wires coming off the switch tomorrow. I went ahead and replaced my headlamp switch with one from NPD, the AutoZone one was a piece of junk anyways. Still didn't help though. Are the tail lights the only thing powered by that fuse? What else should I check?

 

[JWagner]

Ok, I am a little con-FUSE-d here. When my tail lamp fuse failed, my instrument panel lamps also went out. Is the instrument panel lamp fuse getting its power from the tail lamp fuse? I only state this because the oringinal post mentioned panel lamps and tail lamps together, but the follow up suggests that they are separate. And my experience matches the original post.

 

[elkyD68]

John will probably clear this up but as I understand it now the instuments get power thru the taillight fuse because they are switched off the headlamp switch but are fused again seperatly with the small fuse. Probably because so much can go wrong under the dash.

Is that about right?

 

[John_Muha]

"Ok, I am a little con-FUSE-d here. When my tail lamp fuse failed, my instrument panel lamps also went out. Is the instrument panel lamp fuse getting its power from the tail lamp fuse?"

True Jeff, excuse me if I have the name wrong. It's been a while since we "talked". The output of the dimmer rheostat, the green wire, is connected to the short instrument panel fuse. From there the color switches to gray. In a sense the dash lamps are double fused because the headlight switch orange wire is also a fused wire.

"I only state this because the oringinal post mentioned panel lamps and tail lamps together, but the follow up suggests that they are separate. And my experience matches the original post."

Again true. If the problem is past the dash fuse, then that should be the one going out. But what if the problem exists on the rheostat output? The green wire from the headlight switch to the fuseblock? Which fuse would pop? Not the instrument fuse but the tail light fuse, the input orange wire to the switch.