Fusible link fried - what to check before replacing

[Sixpactogo]

You mentioned in your 1st post that you "connected some wires the wrong way". What did you mean by that? If it was the battery, that would have taken out your fusible link.

 

[mr_spock]

You mentioned in your 1st post that you "connected some wires the wrong way". What did you mean by that? If it was the battery, that would have taken out your fusible link.

Ammeter terminals, thought I said that, sorry if that wasn’t clear

 

[LowBikeMike]

Did a bit more diags yesterday. The alternator has a Carquest sticker on, code seems to be a 100A alternator. No idea why, there’s nothing that would need that capacity, but whatever. The resistance from the output stud to ground is about 14 ohms. I have no idea if that’s ok, but it’s not a short to ground. I have an alternator (a 1 wire GM) on my 57 Plymouth and the resistance on that is about 38 ohms, so same order of magnitude. Any thoughts on that?

The reason I ordered the repro fusible link, even at that price, is that it does indeed come with the correct blade connector, and there are 2 wires anyway, one being the fused link and the other is just a wire. So by the time I’d pulled the old one apart, tried to detach the connector, sworn at it, cleaned it etc. it would be another couple of weeks and I’d like to drive it before the weather makes that unpleasant.

So I don’t think I’ve found an obvious cause except the cigar lighter, which I can’t imagine is it. When I get the new link installed I’ll meter it all again and see if I can find anything. Last think I guess could be the starter relay, but that checks out OK too.

If you are checking resistance to ground from the Alt output stud you must disconnect all wires that are attached to the stud to get a proper reading. You really cannot check for grounds in a wire unless both ends of the wire are disconnected. Ohmmeters are for checking isolated circuits.

 

[Nacho-RT74]

Cigar lighter still being on the “batt” side circuit should get its own fuse, so this will blow before the fuse link.

And about the 100 amps alt. Even still with that output capacity doesn’t mean will put that power out. The alt just provide the current is requested as far is able to. A high output alt is a guarantee of a good/decent/better output capacity at slow speeds ( iddle ), so close to nothing discharge status from batt

 

[mr_spock]

Thanks, I do understand how to use a meter. Been doing electronics for years! The alternator wire is fine. I was wondering if the alternator might have an internal short. Also yes I know the 100A is only delivered if there’s a draw needing it. I didn’t know it gives better output at idle, thanks for the new info!

 

[Nacho-RT74]

That would be ( and is posted on all my posts about ) the first and main reason to proceed with the alt upgrade… the iddle capacity. Althought the pulley diameter must be considered first. Smaller as posible to get better juice at lower engine rpms. Not for race cars though, just street “driver“ cars

 

[mr_spock]

Following up..

Did some more diagnostics. The alt to firewall wire is fine, not grounded. The firewall to dash red wire is also fine. The fusible link has visible green corrosion where the insulation split, but there are no marks of heat. This makes me wonder if the link insulation was damaged and some corrosion caused a “hot spot”.

I noticed the ammeter terminals were wobbly, so I pulled it out. Both terminals were loose in the plates to which they attach, and the internal insulation is broken - not such that the terminals hit ground while on the bench, but who knows once installed? I’ve swapped in a spare one which looks perfect. Bad one on the right in the pic (or bottom, since it’s rotated).

more soon…

 

[Nacho-RT74]

The loosen studs and cracked insulator failures has been covered several times around with pics and fixing methods… for those who still want to keep the original design in safe working order (which is really possible)

 

[mr_spock]

Cool. As I said, I have another one without the damage so I wasn't needing to repair it just now, but will look for future reference.

 

[not so famous bob]

View attachment 1548397

thats mind "melt !"

 

[mr_spock]

I think I found the problem! Having tested everything separately I put the dash back in. Lo and behold, there is a short from the positive to negative battery leads (battery not connected). Unplugged the bulkhead connection, no short.

Turns out both ammeter posts are grounded. Bear in mind this tested ok on the bench. Took dash out again, looks like the ammeter moved slightly down in the housing and grounded on the cluster casing. Which is probably why it was ok lying down!

Used some electrical tape around the posts to test my theory and it checked out fine. Will insulate the posts with heat shrink and hope I’m good to go.

 

[Nacho-RT74]

The insulator gets two small side cuts or slots which should locate the ammeter propperly centered to the housing, since the housing gets two keys for it and save from move out its place.. It’s weird.

rallye cluster on pic, but pretty much the same on everyone.

unless the insulator is wavy on the ends and is not able to catch the keys.

if so, IMHO its time to replace the insulator… or maybe get it reversed, but there is a chance to break it due its age and use.

at the same time I’d check the studs play to the shunt.

on a side note, this could be a prove a propper check AND mantenience is allways good for a charging system including the ammeter. For those who allways keeps debating about what is a mantenience Or service on this setup. Which doesn’t mean is a bad thing. The age and use ( and normally, also the abuse ) makes it’s job

 

[mr_spock]

Thanks! Insulator is perfect (see pics), and I re-mounted the ammeter to make sure it was in the keys. But... it's not that.

I am kicking myself.

The old ammeter was indeed a problem, and the new one isn't. Guess why I was getting a path to ground when the cluster was wired up?

The clock.

When the clock points are closed, they are a path to ground. Of course, they open as soon as power is applied (or burn out I gess, but mine are good), but testing before I connected the battery meant they're closed. So there's a good ground. Clock disconnected, no ground. Points open, no ground. Aargh!

So I'm going to be brave and go for it.

 

[RJRENTON]

I think I found the problem! Having tested everything separately I put the dash back in. Lo and behold, there is a short from the positive to negative battery leads (battery not connected). Unplugged the bulkhead connection, no short.

Turns out both ammeter posts are grounded. Bear in mind this tested ok on the bench. Took dash out again, looks like the ammeter moved slightly down in the housing and grounded on the cluster casing. Which is probably why it was ok lying down!

Used some electrical tape around the posts to test my theory and it checked out fine. Will insulate the posts with heat shrink and hope I’m good to go.

Turns out both ammeter posts are grounded. Bear in mind this tested ok on the bench. Took dash out again, looks like the ammeter moved slightly down in the housing and grounded on the cluster casing. Which is probably why it was ok lying down!

I believe I suggested this possibility in my post #9 to you. Glad you got everything fixed....
BOB RENTON

 

[mr_spock]

See my last post … that wasn’t all of it! The clock has thrown me off too. But yes, your post is what had me pull the ammeter and check

 

[Nacho-RT74]

Yes I can see the insulator, but the sides looks to be slightly lifted up. That could make it catches the keys initially but when manipulating the cluster then move on its place. Just a thought.

I’m agree this is somehow a weak point on the design due the material used. I guess never thought our cars would last long 50-60 years. Sure they decided to use this material being heat resistant and non flammable. For a material replacement as an option to the original I would use the PCB board material (Without the metal layer of course), never a plastic/rubber material. Just an opinion.

about the clock… dunno what to say

 

[Don Frelier]

I don't think there is a problem with the clock.
It's essentially a winding so with the points closed it will read as a short just as a coil or electric motor would.

 

[mr_spock]

Thanks for all input - insulator is fine and flat, must be an artefact of the wide angle shot.

Yes, I agree, there is no problem with the clock. But it fooled me when checking with the meter into thinking there's a short to ground which caused the fusible link to fry. Anyway, I found I'd left out two of the colored lenses from the dash so I needed to pull it all out anyway!

More soon.

 

[mr_spock]

Just for closure (don't you hate it when people abandon a thread?)..

It's fine now. The car now starts and runs fine, I'm pretty certain it was a combination of:

1. Damaged fusible link (maybe)
2. Ammeter posts loose, insulator damaged and therefore grouding inside the cluster
3. Me being confused by the clock providing a tiny ground when not wound up!

Now back to the original reason I removed the cluster - fuel gauge!