95 legacy keeps blowing fusible link

[hogweed]

i replaced the solid wire temporary fix and it looks like a good idea i did. i put a wire with a fuse holder in and now every time i start the car the 30 amp fuse gets fried. the wipers go on for one pass even though the switch is off, so i removed the wiper fuse and tried it and it still blew the fusible link. anyone have expereince with this? or do i just have to do a lot of electrical troubleshooting?

thanks in advance.

gregg

[idosubaru]

very strange indeed. any chance you can list recent work done to the car? often times something like this is traceable to something that was worked on previously.

 

i'd try removing ALL the fuses in the fuse box. see if it blows. then insert them one at a time and keep testing until you find what circuit is causing it. that will narrow it down alot at least.

 

on older generation i've seen shorted wires above the gas pedal. there's a wiring connector there that will short out and cause issues. never heard/seen of this on the newer gen but i would look there as a quick check. i attribute it mostly to manual trans cars in the north......snow sticks to your feet and if any gets on the connector and shorts it out over time it'll heat up the connector and cause issues. but it happens on auto's too. usually strange lighting issues before fuses start blowing.

[cobalt]

Hogweed; Is the fusible link ahead of the main fuse panel? One way to eliminate each circuit would be to take all fuses out of panels under the hood and under dash making sure you mark and identify each one as to the plug it came from,and see if that clears the blowing fusible link. Then put them back in one at a time as you try to start the car each time . Maby that will direct you to the problem...Good luck!

[hogweed]

thanks. i was going to do it the other way-take each fuse out one at a time but i was thinking that would blow out a bunch of the 30 amp fuses until i found the right one! i like your idea better. i just bought the car so i don't know about any work other than new valve covers and an oil change. car does have a bunch of surface rust under the hood; could this cause a bad ground in the ignition circuit?

thanks agiain.

gregg

[hogweed]

another thing i remember. when i picked up the car i couldn't take it out of park after i started it; i could hear the relay clicking as i depressed the brake but the shifter would not move. on a hunch i unclamped the adjustment for the column and when it moved down the relay kicked in and i could move the shifter. the next tme i shut it off was when the fusible link went for the first time. could it be a short in the column? that might explain the wiper thing....hmmm

[cookie]

column shorts happen every now ant then because of all the movement. Go to a truck place and get a heavy circuit breaker. Then you can test all you need to and it will just pop.

[Cougar]

If you have a ohmmeter, you can use it to help eliminate the various circuit paths to find the correct one.

[ron917]

I second the ohmmeter idea. Remove the battery, take out each fuse one by one, and measure the resitance between the load side of the fuse and ground. When you find a very low resistance, you've found a suspect cirucit.

[hogweed]

I second the ohmmeter idea. Remove the battery, take out each fuse one by one, and measure the resitance between the load side of the fuse and ground. When you find a very low resistance, you've found a suspect cirucit.

i've used a volt meter before but i don't think i have used an ohm meter. can you tell me specifically what to look for?

thanks.

gregg

[ron917]

A short circuit will theoretically read 0 ohms on an ohmmeter. In reality, the wire and connectors have some resistance in them. If you find a reading of 1 ohm or less, you are definitely looking at a short. Some high current circuits, like the starter, may read very low, so be aware of that.

 

If you are blowing a 30 amp fuse, using Ohm's Law, we know that the circuit must have a resistance of less than 0.4 ohms. (12 volts divided by 30 amps = 0.4 ohms). Add in a max of about half an ohm for the wiring to your meter, the connectors, and car wiring, and we know we are looking at less than a 1 ohm reading on the meter (my meter reads 0.3 ohms for a dead short, see what yours reads by touching the leads together).

 

Remove the battery, disconnect both positive and negative leads before starting. DO NOT SKIP THIS - you could damage your meter, your car, and/or yourself!

 

Remove the fuse for the circuit you wish to test.

 

Then, you need to figure out which side of the fuse socket leads to the circuit you wish to test. I haven't been inside of my Subaru fuse box, but if you can get into it, you'll see that one side of each socket fuse connects to the positive power from the battery, and the other side has a wire (or wires) that lead to whatever cirucuit that fuse powers. If you can't figure it out that way, use your ohmmeter. Connect one lead to the positive battery cable (you disconnected it, right?) and touch the other to one side of the fuse socket - the side that reads a short circuit is the battery side, the other is the load side.

 

Now, connect one lead of your ohmmeter to a solid ground or the negative battery cable (you DID disconnect it, right?). Touch the other lead to the load side of the fuse socket and take your reading. If necessary, turn onthe ignition switch or whatever causes the fuse to blow. Is it less than 1 ohm? If so, you've found your bad circuit.

 

Next, you have to find where the ciruit is shorting out. You need to disconnect each item on the circuit and check it for a short. You need to check each connector and wire in the circuit for shorts. You need a wiring diagram to do this properly, but you might get lucky and find something obvious.

 

This is can be a time consuming process, but you will find your problem if you keep at it.

[hogweed]

thank you for that very simple to foloow procedure. i will try to get to it this weekend and run it down. i'll let you know how i make out.

thanks again to everyone who posted suggestions.

gregg

[Cougar]

Measuring resistance of a circuit is easy to do. You just need to do things a little different than when measuring voltage. Most test meters are made to measure voltage, current, or resistance. You just need to set up the meter and the circuit the proper way to do the measurement you want.

 

Whenever measuring resistance in a circuit the main thing to remember is that no power should be applied to the circuit you are trying to measure. The meter's internal battery will supply the necessary current to measure the circuit and read that measurement out in ohms. The meter leads usually stay in the same position on the meter as they would when you measure voltage. The functione switch of the meter will need to go to the ohms position. Some meters use the Greek sign 'omega' (looks like a hosreshoe) for that since it is the sign for resistance.

 

By removing the ground lead of the car battery you will assure that there is no power getting to the circuit you want to test. Since the fusible link is blown, power will be removed also to circuits downstream of the link and the battery. By placing the meter function to resistance and the meter leads across the load you will see what the resistance is of the circuit. Tie the red lead of the meter to the protected side or 'accessories' side of the fusible link connection and the black lead to a good ground. The meter will show a real low resistance which is going to be really a short. You can then start disconnecting things to help show you what path the short is on. When doing this test, make sure nothing is set to ON in the car, including any lights, as that will intefer with the reading. When you find the right path, the meter resistance will go up fairly high when the connection is broken to the short. By following the short path you will find the problem.

 

If the fusible link is blowing with nothing really on, including the ignition, then I would check the steering column first since constant power appears there tied to the ignition switch.

[cobalt]

I second the ohmmeter idea. Remove the battery, take out each fuse one by one, and measure the resitance between the load side of the fuse and ground. When you find a very low resistance, you've found a suspect cirucit.

 

This is a good idea except for the light circuits. You will see a low resistance ground through the bulb filament to ground on each of these circuits and could lead you on a wild goose chase. :-\

[hogweed]

i'm in the process of checking it out and i noticed that there is what appears a load on the motor before the link blows out. could this just be normal in the sense of all the power being taken away from the system after it blows? the engine stays running even w/out the link

[Cougar]

This is a good idea except for the light circuits. You will see a low resistance ground through the bulb filament to ground on each of these circuits and could lead you on a wild goose chase. :-\

 

You are correct. That is why all the accessories need to be off. I am assuming that the link is blowing while nothing is turned on in the car. This will lead you to the ignition switch area as the fault point since it one of the areas that is hot at all times. The problem may also be near the fuse panel.