One step forward two back! Electrical fun!

[AliK]

Having finished playing with the brakes, I decided to have a quick test drive / trash.

Mid-thrash, putting a fast Audi into its place behind me, all of a sudden all the dash lights went dark and voltmeter showing below thee minimum mark (goes lower if engine not running). Headlights work but none of the interior electrics do not even the heater fan.

I made it home but clearly no charge is coming through as the battery has been discharging and currently sitting at 12.1v not the usual 12.7v.

The alternator is simply too hot to touch for more than a second. Not sure if it’s toast or if when it’s not producing you get major current going though it’s rectifiers which would heat it up.

Given the dash lights and interior electrics have gone, I’m suspecting fusible link issues but all the diagrams I find are for US 260Zs. Anyone have designations for which link is for what and what the ratings they are for a late UK 260?

TIA!

Ps. On the upside having released a stuck brake piston, the car is no longer constantly pulling right when you let go of the wheel!

 

[AliK]

I think I have my answer on the culprit!


Having stripped it back - it looks like the strands have welded themselves together! Gulp!!!

 

[Robotsan]

Blimey.. what happened here then?

 

[AliK]

This is the closest thing to mine - the “lower fusible link pod on mine only has a single with the thick black wire - which I can only assume is alternator and fuse box and probably rated at 40ish amps? On a 280z the black is rated at 80A so would it be the same on a 77 260z?

 

[AliK]

Blimey.. what happened here then?

In short, my own fault! I had the alternator rewound for higher output (90A) and planned to run a parallel circuit with its own 60A fuse / cabling when I was putting in the rebuilt L28 a few years back.

However, time conspired against me and I didn’t get round to it.

I strongly suspect that with the old pulley, the alternator never got into its stride and with the new pulley I fashioned last week for better voltage stability at idle, it’s allowed the alternator to work to its potential. Probably why I haven’t had issues until now.

Moral of the story, respect the laws of electrical engineering!

I’ve got all the bits in the parts bin so probably a job for tomorrow.

 

[toopy]

Does this help? doesnt give amp rating, but could be worked out from info in image, if so inclined.

 

[toopy]

The Amp ratings were quite low from what i remember reading somewhere many years ago, a 40 amp link (Black) and two 30 amp (Green) in our cars.

 

[Rob Gaskin]

So basically your fusible links did their job. Lucky you had them, on a 240Z there is one shown at the alternator on some diagrams but I've not seen one. When I rewired my blue car I fitted a 'maxi' fuse.

Yes always worth considering the size and state of the wiring when upgrading components.

So the next question is 'what is drawing that much current'?

 

[AliK]

Does this help? doesnt give amp rating, but could be worked out from info in image, if so inclined.

Thanks buddy much appreciated. I saw the same FSM page but wasn’t sure what the current rating is as theoretically 1.25mmsq cable is rated at 13A (for comparison 6mm sq this all cable is 60A rated).

I’m thinking I will replace the fusible link with a 40A fuse and add the parallel cable + midi 60A fuse to it (which should give me a little overhead.

I’m disappointed in my self as I still can’t believe that with all my electrical experience I didn’t do this job sooner! Especially as I’ve been berating the POs electrical hacks!

 

[AliK]

So basically your fusible links did their job. Lucky you had them, on a 240Z there is one shown at the alternator on some diagrams but I've not seen one. When I rewired my blue car I fitted a 'maxi' fuse.

Yes always worth considering the size and state of the wiring when upgrading components.

So the next question is 'what is drawing that much current'?

I had the same thought Rob on the draw. I was running the lights, heater motor and cooling fans + having worked on the car earlier, I must have drained the battery quite a bit.

All perm on Lights: 15A
LED brake lights: 1.5A
Heater: est 5-8A
Cooling fans: 8-10A
Ignition: 3A
AFR sensor: 3A
Battery:???
It all adds up quickly eh!?

Also a few days back I did short the coil +ve accidentally when the intake pipe to airbox clamp touched it - so I wonder if that also weakened it? I plan to replace all the links with blade fuses - at least they are easier to come by.

 

[Huw]

it? I plan to replace all the links with blade fuses - at least they are easier to come by.

One thing to bear in mind Ali. Fusable links are designed to withstand an over current for longer than a normal fuse. So if you get a short spike a fuse will blow straight away, where as the link won’t.

 

[toopy]

This is whats been in my car for more years than i can remember, 2 x 40A and 1 x 50A, i also have blade fuses protecting the rewired headlight circuit, but positioned behind the bracket not on the front as in this pic.
The top cable is connected at the starter motor, where the main battery feed comes in, the red wire on the far right 50A fuse goes direct to the alternator. The three white with red stripe wires are in the same configuration as they were with the fusible links. The alternator wire was original ly spliced in further down the loom, hence the two wires together.

But will be looking to replace it at some point with one of these instead https://www.12voltplanet.co.uk/mega-midi-fuse-power-distribution-box.html

 

[Alphabettispaghetti]

Mr K. Just get on and do it properly.

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[AliK]

Nice setup @toopy!!

Good advice @Huw - I figure I rather have a blown fuse when I short something out than a smouldering piece of wire. But I take your point there may well be spikes. If there are and this becomes an issue, I can always revert back to smouldering wires

So, it all began today but children on holiday stoped play!

I found the thin wall AWG6 (16mmsq) cable I a bought all those years back! It’s rated at 55A and a max of 60A. Will run it to a 60A midi fuse just by the fusible links then to the starter positive terminal. Will also run the same cable in black for ground to the starter motor where the battery -ve connects. Although the alternator is pretty well grounded through its mounting bolts and super thick engine earth strap but I figure it can’t hurt while I’m at it and can wrap it into the rest so the loom tape

.

 

[toopy]

My battery is also earthed to the starter motor

 

[AliK]

So, got a bit more done (my 2 hour job turned to a lot more hours)!!

Have all the wiring in place and the midi 60A fuse hidden behind the same bracket as the fusible links. To get the car working again, I soldered back the fusible link (until I buy another) and the car fired up just fine so the alternator is still OK. I left the car running on a fast idle for a while to charge the battery and nothing was smoking thankfully.

Next I need to wrap the cables with loom tape into the loom and prettify it all.

 

[toopy]

Brake fluid a little low there Ali, one more thing to add to the list!

 

[AliK]

Brake fluid a little low there Ali, one more thing to add to the list!

Yep! As you may know, I’ve got a cylinder or two leaking on both front callipers and I recently bled the rear but left the top up, as I will flush the entire system when I sort out the front callipers. That is my next most urgent job! I suspect the seals have gone on one or two of the pistons on each side.

I also had to free off a sticky piston that was making the car pull to the right constantly! So time for a full brake refurb.. Yay!

Ps. Clutch slave cyl is also leaking now so that too is in the cards. Will it ever end!?

 

[Dale]

Will it ever end!?

Well, no.