fuse link in ignition

[SteveO_71]

Since its winter in the NE and the car is sitting in the garage waiting for me to put new rotors / shoes on, I thought I would take some time to better understand the wiring under the hood.

Near the starter relay is a wire (37C) that goes from the relay to junction block, ammeter. alternator, regulator and ultimately main power (37 Yellow) to the ignition switch. This wire has a fuseable link in it. So I'm assuming if this link goes bad, there is no power supplied to the car?

What causes this fuseable link to open? I'm thinking some large current draw from something. How often can this happen and whats it like to replace? Why not some kind of fuse in there?

Also, couldnt the ammeter be disconnected in this area by removing the 654 and 655 wires as opposed to disconnecting under the dash and leaving a power wire ( taped and wrapped under there). I'm ultimately going to replace the ammeter with RCCI voltmeter.

Here is a cryptic pic of what I'm seeing. I'm hoping someone can educate me. Thanks!

View attachment 40905

 

[rvrtrash]

The fuseable link will open with a high current draw like a short circuit. It's essentially part of the wire, so you don't have to worry about corrosion and such. The main wire is large and difficult to solder, especially on 45 year old wiring. I'm not a fan of using common crimp connectors and Harbor Freight crimp pliers, especially on higher current applications. There are industrial connectors and pliers, but the pliers can run a couple of hundred dollars. You would still have the potential for the fuse/ fuse holder developing corrosion or some other bad connection. Think how light sockets sometimes get corroded. The ammeter wires are in the main harness, one under the battery tray and the other about in the middle of the crossmember, IIRC. It would be much easier to use one of the ammeter wires and seal the other with heat shrink.

 

[Don C]

Yes, because this is a shunted ammeter you can disconnect the 654 and 655 wires under the hood when installing the voltmeter. I agree, this is safer than having hot wires with taped ends dangling under the dash. You don't want to use either of them to power the voltmeter, because then the voltmeter would be drawing power continuously.

On older cars that do not have a shunted ammeter all of the power runs through the ammeter and disconnecting the ammeter would disconnect the entire electrical system, unless a bypass jumper were used.

 

[rvrtrash]

 "You don't want to use either of them to power the voltmeter, because then the voltmeter would be drawing power continuously."

I agree with this. I overlooked that in my previous post.

Steve

 

[SteveO_71]

Thanks for the info!

 

[midlife]

The fusible link is also there (on a tach dash car) to prevent the alternator from providing an excessive amount of current to the battery. This can only happen if the battery + side shorts to ground, a most unusual occurrence. On a tach dash car, the car will continue to run from the alternator, but once the fusible link blows, you'll be unable to start the car again.

A crappy engineering design, yet it was used for years from 71 onwards.

 

[NOT A T5]

The fusible link is also there (on a tach dash car) to prevent the alternator from providing an excessive amount of current to the battery.  This can only happen if the battery + side shorts to ground, a most unusual occurrence.  On a tach dash car, the car will continue to run from the alternator, but once the fusible link blows, you'll be unable to start the car again.

A crappy engineering design, yet it was used for years from 71 onwards.

WELCOME back Randy, YEAH!