wisconsin_quat

I did the heater core about a month ago and have not had dash lights since... The small 5 amp fuse keeps blowing and I'm struggling to find the source. The only lights in the whole cabin are:

Climate control
Warning lights.... ABS, CEL, etc etc...
Outside temp display

I recently replaced the instrument cluster, the old one was fried because I sub'ed a 10a fuse in place of the 5a fuse.... (ya smart, I know)...

The car is a 96 A4 2.8 5 speed... What makes this worse is that the car belongs to my sisters friend...

I'm not a big fan of reading electrical schematics, so if someone would like to take a look at what is on the fuse 5 circuit, it would be much appreciated... Winnar gets 10 burrito points...

WJM

Did you touch any of the grounds?

kuthair

I was gonna say to try a 10amp fuse but guess you already did. =P

Audiboy

Looking at a schematic might not help since it might just tell you what end components depend on the power source, but each of them may not be bad.

I would start looking around areas of dense wiring and see if anything where crimped or kinked.

Good luck

Audiboy

If the fuse is cleanly cut, with no burn marks in the plastic casing, then it blew out because the current requirement barely exceeded it's rating. So, the next larger fuse maybe used for emergency.

If the fuse housing shows burnt marks, then it blew out rapidly because of sudden and large current surge - caused most likely by a short circuit. A larger fuse will only cause the next weakest link to be the fuse. This could be the end component (if you're lucky) or the wires - which often is a cause of fire.

wisconsin_quat

That there is a short somewhere?? I'll have to do the same on my GF's car and see what I get. Right now I'm going to try replacing the ignition switch and see if there is any difference at all. Just as of late the turn signals stopped working...

Audiboy

measure a voltage differential accross it's two probes - that's how it calculates resistance.

What this means is what if it is not a short, but a large current consumption - let's say 15 Amps. The voltmeter might show 0 ohms because it will not have any current from it's tiny batteries to supply any of the 15 amp requirement, so that the two probes will read a slight voltage difference. Large voltmeters with low ohm settings might give you a better reading.

If your voltmeter has an ammeter function, then you can use it - but install a fuse in between. Most ammeters are only 10Amps or less. If your short consumes more than that, you'll fry your ammeter. So, get an inline fuse holder, install a fuse the same or slightly less than your ammeter limit, and then probe the fuse connection. If there is a large current drawn, then it's most likely a component failure, and not a wiring short. A wiring short will just max out the ammeter and blow the inline fuse you installed.

Maybe you can go to an autostore and rent a current strobe. What it does is applies current pulses from the fuse, and then you can use a magnetic pick up tool to scan the wires until the magnetic field stops. That's where the short would be.

When I trace for electrical shorts, I've used a similar tool in the shop. But my basic tool is a test light with a decent sized bulb. If the short is greater that the current required by the bulb, then the testlight remains lit - because the other side is positive. I then play with components and wiring - pulling wire connectors if any, until the light goes out. That means I broke the connection to the short, so it will be easier to trace.

computrtutr

The most common cause of that fuse blowing is the wire bundle feeding through the trunk hinge- usually, one of the wires will give up and break, then short against something else. In light of the evidence that this may be related to your heater core replacement, I would pull the dash out and very carefully put it back in, making sure you're not pinching anything. Instead of resistance, I would use a continuity meter to determine that both sides of the fuse are shorted to ground (I don't trust resistance readings for this type of thing). If they both read continuity to the chassis, then a wire is grounding out somewhere in that circuit. Good luck!

wisconsin_quat

would you mind explaining the difference between continuity and resistance?

computrtutr

Continuity is present wherever there is a real, finite value for resistance. Where resistance is infinite, you have an open circuit.

I don't like using ohmmeters to check for continuity because there are so many different types of resistors/devices that may cause funny readings. To check continuity, I prefer to use the continuity setting on the meter to give me a yes/no answer. It might be a funny fluke of mine, but it's my preference.