Fusebox circuit diagnosis / MSA box questions

[Jetaway]

Greetings,

Hope everyone had a chance to run around in their Z this Labor Day weekend! I didn't;(

The fusebox in my 1972 240Z decided to part ways 50 miles from home last week. It appears as if the wiper circuit (Accessory) overheated, melted, and shorted into the flasher (Ignition) circuit causing a quick end to the outing. (Not to mention the ignominy of having it hoisted high onto a flat bed like a vanquished enemy and delivered home. The shame, the shame...) I've already ordered the upgraded box from MSA and should be able to get to it later this week. No fuse blew during the meltdown, in fact, I wasn't using the wipers, and haven't in months, which makes me suspect it was a moldering (smoldering?) long-term issue which finally raised its head. I hadn't overamped the fuses either. No burning odor either. A few questions:

1) I replaced and upgraded the OEM alternator with a 60 amp ZX version. A friend of mine claims this might be the problem. I think a few more amps pumping through the system, at most, hastened the wires demise, but would have eventually occurred. Probably in December. In the rain.

2) Having no desire to see a new $200 part go up in smoke, I'd like to be able to trace the problem to something in particular. Other than the burned wire(s) though, I don't know how to proceed. Neither of the big power users (headlights and wiper) were in use at the time and my audio, a somewhat modest user of power, is in-line fused directly to the battery save for the head unit trigger. Any usual suspects to start with or suggestions on what to test for and where?

3) I will admit to the rank amateur method of tapping into the old box using the wire under the fuse technique. That won't be possible with the new-style fuse MSA box. One circuit is interior and instrument LED lighting which I switch manually. This I can wire to the battery if need be. The second are LED footwell lights which I controlled by tapping into the dome light circuit and the third is the radio head unit trigger, which I had on the Accessory circuit. Is it possible, or I guess I should say, possible and wise, to run these wires to the underside of the MSA fusebox to retain their functionality? If not, where would be a handy and safe place to tap into the dome light and Accessory circuits?

Thanks!

Chris

[SteveJ]

I'll post a diatribe on wiring later.

[Jetaway]

I'll post a diatribe on wiring later.

HAHAHAHA!

Thank you, but first my brothers and sisters, join me in laughter to dry away my tears.

HAHAHHAAA!

Deciding that this was a better time than most to go through and clean up or out the electrical hacks that I and POs had done, I've spent a good deal of time on my side or my back peering into the hidden interior of my Z. After determining that a hanging butt connector probably went to a nearly hidden butt connector above it connected to a buzzer (my guess -- key in ignition with door open) my gaze shifted to the steering column and: "What is this? A six-pin connector not connected to anything?" Indeed it was and should have connected to the ignition switch.

HAHAHA!

Cripes. No doubt, given the damage I've discovered it was time to replace the old fuse box and to the extent I was pushed forward by the breakdown, I am glad. But the $500 in fines, confiscation fees, freeing the Z from jail and the tow home -- arrrgghhhh!

But now I'm struck by a puzzling thought. My Z would turn over normally, it just wouldn't fire up. If the connector had slipped off, how would the starter turn over? Different connection perhaps?

Chris

[SteveJ]

Greetings,

Hope everyone had a chance to run around in their Z this Labor Day weekend! I didn't;(

The fusebox in my 1972 240Z decided to part ways 50 miles from home last week. It appears as if the wiper circuit (Accessory) overheated, melted, and shorted into the flasher (Ignition) circuit causing a quick end to the outing. (Not to mention the ignominy of having it hoisted high onto a flat bed like a vanquished enemy and delivered home. The shame, the shame...) I've already ordered the upgraded box from MSA and should be able to get to it later this week. No fuse blew during the meltdown, in fact, I wasn't using the wipers, and haven't in months, which makes me suspect it was a moldering (smoldering?) long-term issue which finally raised its head. I hadn't overamped the fuses either. No burning odor either.

The fuse also powers the reverse lights and the AT inhibit switch. (Was your car ever an automatic?) I would suspect the flasher circuit failed first and took the other circuit with it.

A few questions:

1) I replaced and upgraded the OEM alternator with a 60 amp ZX version. A friend of mine claims this might be the problem. I think a few more amps pumping through the system, at most, hastened the wires demise, but would have eventually occurred. Probably in December. In the rain.

That really isn't correct.

The alternator will only output more current if the system asks for more current. If a particular circuit branching off the fusebox needs only 2 Amps, it won't get more than 2 Amps with a higher capacity alternator.

Current is the flow of electrons. Think of the alternator as an electron pump. Now consider a small town that uses 40 gallons per hour (GPH) of water. The water plant pushes out 40 GPH to meet the town's needs. Even if the plant installed a pump capable of 100 GPH, it would still only pump out what the town needs.

On the other hand, if you keep adding customers (circuits) to the system without upgrading the mains, the extra demand could cause the mains to fail. The branch circuits would be unlikely to fail in that scenario.

2) Having no desire to see a new $200 part go up in smoke, I'd like to be able to trace the problem to something in particular. Other than the burned wire(s) though, I don't know how to proceed. Neither of the big power users (headlights and wiper) were in use at the time and my audio, a somewhat modest user of power, is in-line fused directly to the battery save for the head unit trigger. Any usual suspects to start with or suggestions on what to test for and where?

Corrosion - at the connections, rivets, crimps, fuse holders, screws, grounds, etc. Corrosion is the atherosclerosis of the electrical system. Except in this case, the disease will manifest itself as heat. That can eventually destroy wires.

3) I will admit to the rank amateur method of tapping into the old box using the wire under the fuse technique. That won't be possible with the new-style fuse MSA box. One circuit is interior and instrument LED lighting which I switch manually. This I can wire to the battery if need be. The second are LED footwell lights which I controlled by tapping into the dome light circuit and the third is the radio head unit trigger, which I had on the Accessory circuit. Is it possible, or I guess I should say, possible and wise, to run these wires to the underside of the MSA fusebox to retain their functionality? If not, where would be a handy and safe place to tap into the dome light and Accessory circuits?

No, you cannot run wires to the underside of the MSA fusebox. You run the risk of shorting out the circuit under the fusebox.

You can remove a small ring of insulation from the wire you want to tap and solder the new circuit wire onto it. Then wrap it in electrical tape or use liberal amounts of liquid electrical tape.

The problem is that you need to know the current that is flowing through the circuit and the current draw of the new circuit. Will the total current be greater than the ampacity of the wire? See page 14 of this document. Keep in mind that the fuses in the car are designed to protect the wiring, not the components. At 20A, the fuses don't allow much room for error on many of those circuits. It tempts me to re-look at my own fuseboxes and consider 10A or 15A fuses for the circuits that currently have 20A fuses. (15A would be better, but I have to see if they come in the proper class for the old glass fuses.)

LED lighting doesn't create much of a current demand, but just be careful in your execution.

[Jetaway]

The fuse also powers the reverse lights and the AT inhibit switch. (Was your car ever an automatic?) I would suspect the flasher circuit failed first and took the other circuit with it.

Nope, always a manual. Could be the flasher and I'll check it out, but I have my doubts. First, the insulation on the wiper wire was heavily damaged, crispy even, while the flasher wire insulation appeared to have been melted from the outside in.

That really isn't correct.

The alternator will only output more current if the system asks for more current. If a particular circuit branching off the fusebox needs only 2 Amps, it won't get more than 2 Amps with a higher capacity alternator.

Current is the flow of electrons. Think of the alternator as an electron pump. Now consider a small town that uses 40 gallons per hour (GPH) of water. The water plant pushes out 40 GPH to meet the town's needs. Even if the plant installed a pump capable of 100 GPH, it would still only pump out what the town needs.

On the other hand, if you keep adding customers (circuits) to the system without upgrading the mains, the extra demand could cause the mains to fail. The branch circuits would be unlikely to fail in that scenario.

I know this at an intellectual level, but I've seen installing a new alternator followed by wiring problems within the month before. Could well be marginally higher voltage with the new alternator. I hadn't adjusted the external regulator in the four years I've had the car. Can't say any dramatic difference, the headlights seemed a little brighter, but that could well have been expecting them to be brighter.

Corrosion - at the connections, rivets, crimps, fuse holders, screws, grounds, etc. Corrosion is the atherosclerosis of the electrical system. Except in this case, the disease will manifest itself as heat. That can eventually destroy wires.

Could have snuck in but in four years I've been through just about every electrical connection and I'm a fanatic about cleaning them up. Doesn't mean something isn't hiding in the bowels though. The flasher circuit should be in good shape, the lights in the tail are LED and I replaced the old flasher with a modern electronic one about a year ago.

No, you cannot run wires to the underside of the MSA fusebox. You run the risk of shorting out the circuit under the fusebox.

You can remove a small ring of insulation from the wire you want to tap and solder the new circuit wire onto it. Then wrap it in electrical tape or use liberal amounts of liquid electrical tape.

I was afraid of that. Solderdrops falling on my head ... (Apologies to B. Bacharach, I believe it was.)

I have an idea on how to avoid slice, tap, and solder with the radio trigger. All Z's, at least the U.S. models, came standard with AM/FM radios. My original radio was gone, replaced by a Phase Linear unit which most assuredly does not use the original wiring harness. I've found a few orphaned connectors in the console. One, fairly large, is a T connector. Then there are two, rather smallish, flat 3-pinners with only the outside positions used. Could the T connector be power, switched through Accessory and the other two the speaker connections to the original?

Chris

[Jetaway]

Greetings,

Hope everyone had a chance to run around in their Z this Labor Day weekend! I didn't;(

The fusebox in my 1972 240Z decided to part ways 50 miles from home last week. It appears as if the wiper circuit (Accessory) overheated, melted, and shorted into the flasher (Ignition) circuit causing a quick end to the outing. (Not to mention the ignominy of having it hoisted high onto a flat bed like a vanquished enemy and delivered home. The shame, the shame...) I've already ordered the upgraded box from MSA and should be able to get to it later this week. No fuse blew during the meltdown, in fact, I wasn't using the wipers, and haven't in months, which makes me suspect it was a moldering (smoldering?) long-term issue which finally raised its head. I hadn't overamped the fuses either. No burning odor either. A few questions:

Actually finished up on the job a couple of weeks ago, but only had time for extensive driving in the last week. It took me awhile, probably longer than it should have because I have a tendency to sit and contemplate my next move, particularly with electrics.

With the old fuse box I used the rank amateur method of hooking a wire under the fuse for a connection. Couldn't do that with the MSA modern type fuse box. I looked around under the dash, looked at schematic(s), tested circuits, looked under the dash, etc. I ended up using the following connections.

As the trigger for the audio head unit and the Sun tach I installed where the original clock was located I needed an ignition-on hot connection. Wasn't quite where I expected, but I found the body-side connector for the factory radio sticking out (barely) outside the console on the passenger side. I found a matching connector that wasn't hooked up to anything (What did it do? Where did it go? I know not.) removed it used it to hook the audio and tach up to the original ignition-on circuit.

I have switch controlled interior LED lighting that I wanted on an always-hot circuit. Figured the clock body wire would do the trick and it does.

Finally, I have floor well LED lights that I wanted controlled by the door switches. This one puzzled me for a couple of days until I realized that the positive side should be an always-hot circuit because the door switch circuit operates off the ground. It joined the other interior LED lighting on the clock circuit.

Besides the blower connection, worthy of its on post, I pulled four or five wires to nowhere out of the console area. I further suspect, though I didn't check, that somewhere in there is a pair of wires running to the fuel tank for a pump as the non-US cars used. I say this because I've seen some wires poking out near the tank that wouldn't seem to have any other purpose.

The upshot is that nothing exciting happens. He starts, he runs, he doesn't smoke in inappropriate locations. Sometimes being boring is just right.

Chris