Fusible Link Again

[jbinsure]

Sorry for the additional post.....was just out working on the car and had a couple of questions.

The end of the fuse closest to the battery, is getting hot enough to melt through the plastic covering. The little fibrous type board that the link screws on to is somewhat frayed. Could this be the sole cause of the end getting hot? Has anyone else experienced this type of problem? My SI board is freaking out ( tach, fuel and temp gauges work 1/2 of the time)...could this be causing the fusible link to get hot? The car runs fine, so this annoying problem I believe is somewhat simple, but I cannot figure it out. I hooked up a voltmeter to all fuses, but have no idea what I am looking for as far as readout. Is there anything that I should check?

Sorry all... just very frustrated as I love this damn car, but cannot figure out this problem.

Thanks...again!!!

Jeff

[ShadeTreeBill]

Hey Jeff:

Sorry to hear about your continuing problems. I have not checked in on the forum lately, I have been too busy replacing my bad head gasket on my 89 525i.... Anyway I just went out and looked at my terminal block where the fuse link is mounted.

There is a short heavy gauge wire, probably a 10ga stranded wire that runs from the fuse terminal block to the positive side on the battery. It bolts onto the positive battery terminal. The "main" battery cable is an even larger wire that runs down into the engine compartment. We are not concerned with that one since it is not a part of the fuse link circuit.

The wire that connects to the fuse link terminal block has a metal connector that is crimped (and in my case looks soldered) onto the end of the wire. If this connection is loose and frayed, that could definitely cause that end of the fuse link to get hot.

Here is the theory behind it: Heat is created in a circuit where significant resistance is found. Good solid connections have little or no resistance. A loose, corroded, dirty or rusty connection has significant resistance, and therefore when current passes through that connection, heat is formed as a result of the resistive losses at that point in the circuit. It's sort of like a lamp filament, but of course you do not want this to happen.

Now, as to the dash lights going out suddenly, this could have been caused by this loose, dirty connection at the fuse link terminal block. ( I cannot account for them coming on when you hit the dash, so this part of my take may be off base.) However, a loose connection can pass enough voltage/current/power to operate the equipment, but the connection can be suddenly lost completely due to vibrations, expansion, contraction etc of the connection, causing whatever connected equipment to suddenly cease operation. The same slight changes in vibrations, expansion, contraction etc, can intermittenly restore the operation of the circuit, again with teh associated heat losses caused by the resistive connection.

So, DEFINITELY, you want to fix any frayed, dirty, loose, or otherwise questionable connections on the wiring where it enters and leaves the fuse link terminal block. As I said at the beginning of this post, I look at my connections, and they are tight, shiny, not corroded or dirty.

A final note: High current circuits (like this 80 amp fuse link circuit) have a peculiar characteristic in that if a loose connection develops, then heat and eventually arcing develops. This arcing (read tiny sparks) will further damage the connection raising the resistance even more, and therefore creating even more heat, eventually melting the insulation on the wire, and any plastic components, (the "conduit"). This is classic symptom of a loose connection in a high current circuit. And of course, it could cause the fuse link to burn through again....

Fix your wires.... It would be best if you could get a new short wire from BMW with the connectors already installed. I bet the short wire from the battery to the fuse link terminal block probably is a common replacement part. You may want to replace the terminal block (conduit assy also) if it has been damaged.

Be careful when working around the battery, as it contains an incredible amount of energy, BEST to remove it completely while working in that area, AT VERY LEAST COVER IT with a heavy cloth or rug, I use an old rubber back bath mat I stole from the my wife! If you get a wrench between the positive post and the car body, it could weld in place, over heat the battery and make the battery explode and spray acid everywhere. I don't mean to scare you but the battery is a dangerous thing if precautions are not taken.

BTW: I have been an electronics tech for some 25 odd years so not everything I have written here is valueless....

Hey, can you help me fix my cooling system? Do you know how to get oil out of the heater core? Don't get me started, long story!

Regards,

ShadeTreeBill