Electrical fire yay!

[furyus 67]

Well I did the ammeter bypass when I put my new alternator on. It seemed fine for a bit as I am trying to solve some other issues with the engine itself. So as I'm pulling into my barn,the car dies, smoke coming from under hood,yay. I get the bat disconnected and see that the lead from the bat + to the starter relay is melted and the ammeter/fusable link wire is melted in half. Electrically speaking, the only modification I've made is the the ammeter bypass. That (I thought) was supposed help eliminate the possibility of the fusable link plug catching fire. It melted the contacts in the plug a little bit but fried the wire. So question is " why did I do wrong with this cursed car this time?" Lol

 

[furyus 67]

Also, I still have the 2 wire charging system.

 

[commando1]

I've seen several versions of the "ammeter bypass" floating around and I have found a couple that are suspect in my mind as to the way it is done.

Where did you get your instructions from?

 

[furyus 67]

I've seen several versions of the "ammeter bypass" floating around and I have found a couple that are suspect in my mind as to the way it is done.

Where did you get your instructions from?

I don't remember what thread it was but I'd take the screen shot.

 

[Fury440]

Most of that happened to me and it turned out the battery wire from the alternator to the bulkhead was just touching the exhaust manifold. The wire would bounce against the manifold, spark and make the ammeter jump around. Finally it touched sand welded itself to the manifold and started the great meltdown.

That wire is routed from the alt to the bulkhead, to the welded splice, to one side of the ammeter, from the other side of the ammeter back to a different bulkhead pin, from the bulkhead to the starter relay and finally via the fusible link to the battery +ve post.

Note the ammeter is a serial device that measures the voltage drop across a very low resistance inside thed meter. If the meter lock nuts are loose they will get hot and could start melting wires under the dash. To bypass the meter, just put all the wires connected to the meter on one post and make sure the nut and lock nut is tight.

The best way to "de-load" the bulkhead wiring is to run a #10 wire from the alternator battery post directly to the battery. Use two fusible links, one at each end. Why two you wonder? If the new cable shorts somewhere in the middle, current will drain to the short from both sources, the battery and the alternator. You must size the wire and fusible links to handle the max current the alternator can produced.

Hope this info makes sense and helps.

 

[Wildaugust]

Wow. Never a good day when stuff like this happens, but the fusible link did it's job. How many amps is your alternator?

 

[furyus 67]

I ran a # 10 from the battery lead to the starter relay post. It basically fried the wires connected to the starter relay + post.

 

[furyus 67]

There is still a path through the bh. The way I understood it was by running a wire from the bat lead on the alternator to the bat or the starter relay I would limit the amount of amps running through the bh, this lowering the possibility of this happening. Should I eliminate the ammeter all together?

 

[furyus 67]

Also the meter lock nuts were tight. I tore the dash back apart and there doesn't seem to be any damage from the inside bulkhead to the meter or past it.

 

[Boomer]

The only way you're going to eliminate something is to disconnect the line. I'm not so sure about simply limiting it by adding another path.

Without knowing all the numbers involved (voltage, amperage/current draw etc) it's difficult to say for sure, but it almost looks like your #10 wire was a little too lightweight for the job. Think closer to battery cable size, or maybe #6.

 

[furyus 67]

55 amp alternator. Do you think that short battery/ starter relay lead could have caused it?

 

[Fury440]

There is still a path through the bh. The way I understood it was by running a wire from the bat lead on the alternator to the bat or the starter relay I would limit the amount of amps running through the bh, this lowering the possibility of this happening. Should I eliminate the ammeter all together?

Basically you are providing two paths for the alternator charging current to reach the battery. If for example your charging current is 30 amp, it will split with 15 amp through the bypass and 15 amp through the bulkhead. Where guys get into trouble is they use a giant alternator, say 100 or 120 amps and try to push 50 to 60 amps through the bulkhead. To use those powerful alternators you must disconnect the alt battery connection to the bulkhead and forced all the current directly to the battery. In that case all the current used by the car to run your toys must pass from the battery through the bulkhead to the ammeter. The ammeter would display discharge (current used) but never charging. Remember the factory wiring assumes a 30 amp or smaller alternator, so the wires are sized for that load. Add a bunch of toys and you risk cooking lots of wires. Big audio systems need to be connected directly to the battery, via a fusible link.

 

[Fury440]

55 amp alternator. Do you think that short battery/ starter relay lead could have caused it?

Look at wire size calculators liked this one http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

For 3% loss, a 55 amp cable about 1.5 meter long will need a #7 gauge wire. US wire is typically even number size to you would need #6. At each end you would need a fusible link sized for #6 cable. Noted the fusible link a not a fuse to protect your toys, it is only to protect the wire itself.

 

[Fury440]

Don't get off track with wire size etc, your "burn out" was most likely caused by a short circuit which you must find and repair first.

 

[Wildaugust]

Yeah that.

The 55 Amp alternator may be a little large for a #10 wire though. With a smaller alternator, I wouldn't be at all concerned about having both pathways, directly from alternator via starter relay to the battery, as well as through the BH connector/ammeter. However, with both pathways being used, if something happens to either pathway, all of the current will then, at least momentarily, flow through the other pathway. That's when things might get nasty. So, with a larger alternator, it may be a good idea not to leave the original BH Connector/Ammeter circuit in the loop, so to speak.

 

[Fury440]

.... So, with a larger alternator, it may be a good idea not to leave the original BH Connector/Ammeter circuit in the loop, so to speak.

or just add a #10 wire fusible link at the alternator to protect the car's factory wiring.

 

[furyus 67]

Could the short be in the voltage regulator? I can find no short from the bh to ammeter and back.

 

[Fury440]

I don't think a short there would smoke the fusible link. Most likely you have an intermittent short where the wire goes through a hole or bends around some obstacle. In my case it was the lower corner of my passenger side exhaust manifold.

 

[furyus 67]

Ok, well I've jumped up #8 for the bat/relay wire and am replacing the fusable link at the bh and adding one to the alternator/bat wire. Hopefully I have no more mishaps! I'm going to go through the the wiring one more time to look for the short. Thanks for the guidance gents!

 

[furyus 67]

One more, what's the best way to replace the one bulk head connector? I mean a source for the connections or a whole new engine harness?