fusible link and fuse question

[Burdar]

This will be the last electrical question...OK probably not. Here's the situation.

1. AMP gauge bypassed(will be monitoring volts)
2. 60amp Denso alternator
3. 8-gauge wire from alternator output stud to starter relay

To minimize modifications to a new engine harness, I'm leaving the factory alternator charge wire in place.  The interior will now be fed from two locations.(alternator and factory red wire from battery)  The factory red wire has a fusible link on it.  The alternator charge wire does not.  With no fusible link on the alternator wire(and a bypass to the starter relay) the factory fusible link can blow if there is a short in the interior but current can still flow to the interior from the alternator.  This is why I need to add a link to the alternator wire.

So, first question...what is the factory wire gauge of the stock alternator charge wire?  I saw 12 gauge mentioned online but the wiring diagrams don't say.  If it is indeed 12 gauge, I assume I need to install a 16 gauge fusible link?  How long does the link need to be?(if it matters)

Next question involves the 8-gauge bypass wire.  Is everyone adding a link or fuse to this wire?  The only real reason to add protection to this wire is probably an alternator internally shorting to ground right.  The rest of the system is protected by the fusible links.  If I run a fuse on this wire instead of a fusible link, how do you determine what size fuse to use?  Since the alternator has a max rating of 60 amps, do you pick a fuse just under that rating? 

[Chryco Psycho]

I look at this way you have full battery voltage at the start relay & when running you have more voltage from the alt so which are you protecting from the other , to me it makes no sense to have a fusable link in there .
if the wire were to short in the middle both ends would still be powered.

[mopar jack]

Just ran a bypass on mine and used 10 gauge connected to a short piece of 14 gauge fusible link wire and terminated to the start relay terminal that goes directly to the battery. You can get the fusible wire at most auto part stores. I would hope that a proper fusible wire has enough heat insulation resistance to not burn through and cause a fire.

[dodj]

I used a 100 amp manl fuse.

[Burdar]

@dodj do have a picture of what you used and where you put it? We're you able to hide it?

I'm a little concerned about an internal alternator short. That's a lot of juice flowing through an 8 gauge wire. The factory used a bypass wire on 90s Dakotas. I'm not 100% sure but I don't think it was fused in any way. Maybe I'll look for a Dakota wiring diagram and see.

When adding a fusible link or inline fuse holder, are you using a butt connector, soldering or both?

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[Burdar]

I've got two fuse holders. The first is a standard blade fuse holder with 8 gauge wire built in. The largest amp fuse for this size is only 40 amps. The second one is a maxi fuse holder with a 100 amp fuse in it. The issue with this one is that the wire is held in place with set screws. I had a 4 gauge wire in it at one time powering some amps. It's not weather tight at all with the set screw connections. And it's super ugly imo.

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[dodj]

I'll take a pic when I get out to the garage. I did not try to hide it though. It's mounted on the driver's frame rail below the battery tray

[Chryco Psycho]

I believe the factory ammeter charge wire is 12ga , if you look at the wiring diagram the gauge of the wire is always listed so it will say 12BK for 12 ga Black or 16OR for 16 ga orange etc .
AS I said I have never put a fuse inline even with 160 amp alt . 

[Mopar5]

Very interesting I know in the world of AC current 12 guage is only rated for 20 amps. The other thing thats interesting is AC cycles at 60 hertz (on and off 60 times per second) so theoratically the wire gets a rest every half second.Conversly DC is always on with no cycling. I always wonder why they allow small guage wire for high current application in cars.60 amp residential wire is 4 guage.

[dodj]

Actually, the zero point is crossed every 16.6 milliseconds in a 60 Hz system.
Not that many people will ever use that knowledge... Lol

[Mopar5]

Then that would be 60.24 Hertz. 1000 \ 16.6

[Burdar]

The 68 diagram on mymopar doesnt have any wire gauges listed. I checked it against my Challenger harness and they are the same size. Does anyone have a diagram of a Challenger that shows the alternator wire size? The black alternator wire is smaller then the red wire that enters the bulkhead from the battery.

I'm definitely adding a fusible link to the alternator wire. Still looking for opinions on the bypass wire. I'm not really worried about that wire rubbing through and shorting. Its taped to the main harness and then wrapped. My concern is protecting it from a shorted alternator.

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[dodj]

Standard '73 Challenger alt wire was 12awg. 60 amp optional alt had 8awg. That 8awg wire was spliced onto two 10awg wires. One leg went to the ammeter gauge through it's own grommet at the firewall avoiding the BH connector. The other leg goes the traditional route through the BH connector along with a 16awg fusible link.

[dodj]

Like I said, didn't try to hide it. I also use it as a junction block because my battery is in the trunk.

[Burdar]

@dodj how did you choose the 100 amp fuse?  Why 100 amp?  My alt is only rated at 60.  I assume if there is a dead short, the 100 amp will blow anyway.  Just wondering what size to pick.