67 Monaco- Blows fuse turning key from off to IGN??

[Billy Spence]

Anyone knowledgeable with voltage?

1967 C body, ran great last night. Went to start today, smoked out the red wire that runs from from the starter relay to the firewall and connected up to the ammeter (no ammeter gauge but as per the wiring diagram). Wire replaced put in line fuse and connection checked all the way to the gauge- looks good. L firewall connectors cleaned too.

Went to start, with 10 then 25A fuse, pops soon as key is turned to ign from off, don’t even get as far as crank.

Starter turns and works when jumping the contactors and fuel flow to carb fine.

Can’t voltage test rest of circuit when fuse blows straight away?

Any ideas much appreciated! If I can get key to on position I can prob check the rest of the circuit once supplied with voltage.

 

[traintech55]

When this first happened you blew the "Fusible Link". It is very unsafe to replace this with a fuse. As for the short, it is somewhere in your main ignition, run circuit. Time to get a F.S.M. and trace it down.

 

[thethee]

Get yourself a good multimeter and the FSM. Finding the short without the full wiring diagram is going to be really difficult.

When this first happened you blew the "Fusible Link". It is very unsafe to replace this with a fuse. As for the short, it is somewhere in your main ignition, run circuit. Time to get a F.S.M. and trace it down.

Why is this unsafe?

 

[Billy Spence]

There was no fusible link, I just wanted to have a fuse there till I discovered what the fault was (save further damage).

Iv got the manual and a good multimeter, just wondered if anyone had some pointers. Iv checked quite a bit of wiring but still found no apparent issues.

Run circuit is obviously causing the issue but can’t find it

 

[67Monaco]

There was no fusible link, I just wanted to have a fuse there till I discovered what the fault was (save further damage).

Iv got the manual and a good multimeter, just wondered if anyone had some pointers. Iv checked quite a bit of wiring but still found no apparent issues.

Run circuit is obviously causing the issue but can’t find it

Bypass the damned ammeter and work backwards. Dollars to donuts though it's the connections at the ammeter.

 

[traintech55]

Get yourself a good multimeter and the FSM. Finding the short without the full wiring diagram is going to be really difficult.



Why is this unsafe?

A fusible link, will not react to heat as much as a fuse will. Besides, most fuses are fast blow, that is why they use a link.

 

[1966newport]

if no link someone remove it

 

[Davea Lux]

You should replace the fusible link with an appropriately sized unit, after market universal ones are available at most auto parts. This keeps from frying the whole wiring harness. Get the wiring diagram and start disconnecting or turning off ignition powered accessories until the short is located. Look for a burned spot on the harness, a sure sign of a short. As noted, the ammeters were prone to shorting out. The ignition switches were also known to break the internal components and go to ground, causing a large short.

Dave

 

[Big_John]

IMHO,
There is a short somewhere from ignition switch up to the feed to the fuse block or the ignition run circuit.

It's not in the ammeter... The wire is energized to the ammeter all the time even when the ignition switch is off.

It's not past the fuse block. It's not blowing fuses and if a fuse blew, the feed coming from under the hood wouldn't be frying.

So... That leaves the ignition switch to the fuse block or possibly the ignition run circuit.

If it were after the ignition switch, I would expect it to fry something after the switch, but it's frying before the switch... So it makes sense that (like Dave says) the switch has an internal short.

I would inspect the wiring around the switch, pull the switch and check it.

Once you've established the problem, and I think you'll find it is the switch, then replace the fusible link(s) which is what should have fried when this happened. If other wiring fired... Well, that does sound like the fusible link wasn't in place.

 

[Billy Spence]

Appreciate all your suggestions. No solution yet.

fixed a bunch of poor condition wires (coil blue wire in pic).

I had another ignition and tried it but no joy. The connector to GND isn’t wired up. Could this be an issue?
Also any idea how to jump this with blade fuses to check if it’s the ign that’s bad?

 

[thethee]

Appreciate all your suggestions. No solution yet.

fixed a bunch of poor condition wires (coil blue wire in pic).

I had another ignition and tried it but no joy. The connector to GND isn’t wired up. Could this be an issue?
Also any idea how to jump this with blade fuses to check if it’s the ign that’s bad?

View attachment 443424

View attachment 443425

Not sure what you mean by GND isn't wired up, but I assume you mean GRD? You mean it doesn't have a connector attached or there is a loose wiring hanging from it? Either way, if GRD doesn't have a solid connection, then there is your culprit

 

[Billy Spence]

Sorry yes GRD. The connector block only has 5 slots whereas the ignition itself has 6 pins. Beside it are 3 loose wires that have never been connected (1 red and 2 brown with white tracer- believe for a blower fan that was removed).

GRD never was connected, and it has been working fine like this since I got it 6 months or so ago. Was going to get round to it but this has forced my hand. Even the manual only shows 5 pins?

Should I wire GRD to ground and test it?

 

[thethee]

Should I wire GRD to ground and test it?

Yes

 

[3175375]

Should I wire GRD to ground and test it?

Test the switch with an ohmmeter first.
Then test it with power applied using a voltmeter to verify the switch works with nothing attached at the output connections.
You could then attach each output connection, one at a time.

You will need to jumper wires between the switch and the mating connector, but that approach will lead you to the culprit.

 

[Big_John]

The "GRD" terminal on the switch has nothing to do with your problem.

You have a short to ground somewhere. It's either in the wiring or in the switch. You are saying that the wiring is in poor condition and you've already replaced some, so either there's still more problems or something you did is wrong. Look for add on accessories as a good starting point for trouble or replaced wiring.

The fact that there was no fusible link speaks volumes about the condition of the electrical system. Someone has probably already hacked things up and it's a nightmare (read fire) waiting to happen.

I'd be considering a replacement harness at this point.

 

[3175375]

The "GRD" terminal on the switch has nothing to do with your problem.

...

I'd be considering a replacement harness at this point.

I agree with the first sentence, but not the second - yet.

Before condemning the harness, I believe that additional information (pictures and additional descriptions) IMHO.

 

[dart4forte]

Keep a fire extinguisher handy

 

[thethee]

Sorry, I've made a mistake, like Big John said GRD is actually not your problem.

 

[Billy Spence]

As agreed GRD made no difference.

The ignition itself Ohm tested and works correctly. Just batt feed when off, ignition 1 and Acc at position 1 and at position 2 (run) I have Ign2 and St.

Voltage testing the ignition connector block it has a permanent 12v feed from batt and also Accessory. So there must be an accessory suppling power or an accessory that is shorting.

In addition a few other bits now playing up. Interior lights, should be off when door closed. Door closed - rear interior lights are off and front are on, open the door and the opposite happens? Now going to check supply to doors (fronts obviously have the supply issue).

Going to investigate the accessory circuit now

 

[Big_John]

I agree with the first sentence, but not the second - yet.

Before condemning the harness, I believe that additional information (pictures and additional descriptions) IMHO.

As far as the harness, well... Maybe I'm being premature, but as soon as I read "there were no fusible links" and "I've had to replace damaged wires" and now this problem...