brake warning light - relay bad

[Chickenman]

Ha ha. My Brake check relay just died 2 days ago. 76 280Z. Wasn't sure where the sucker was located. Thanks to Google and Classic-Z!!

[Dreamzz]

ok it worked. i'll be trying it out to see if it melts or catches on fire...
part 1, relay:
12 VDC Waterproof Relay SPDT 30/40A with Metal Bracket
(http://www.amazon.com/gp/product/B000PHLQJW/ref=oss_product)
wire harness:
12 VDC 5-Pin Relay Socket Interlocking Style
(http://www.amazon.com/gp/product/B002QAQVIC/ref=oss_product)
the old relay wire colors ----> new wire harness colors ----> relay pin numbers
black ---- red wire + white wire ----- 85 + 87a
yellow ---- Black ----- 86
green/white ---- Blue ----- 30
I' try to get better pics once i find my camera. and this is for a 1976 280z. Knowing nissan, they probably changed how its wired every model year, if not evey month... [emoji4]

So can you provide an update? Is relay still working?
I need an option for a less sensitive relay. I did the common zx 60 amp alternator upgrade on my 8/75 280z and due to the required wiring or jumping of the voltage regulator wires the brake light relay was slowly draining my battery.
As what I thought would be a solution i ran a new 12v ignition source cicuit from the the stand alone fuse block I installed which must have been to much for the relay....fried it. Leaving me searching for a new relay. Probably could just unplug it but I would like to keep everything on the car working not to mention the safety feature of the brake warning light.


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[Zed Head]

12 volts should not have fried it.  That's what it's designed for.  Are you sure it's dead?

I had the same problem with the battery draining.  The atlanticz wiring diagram doesn't take the relay in to account.  The relay is supposed to get power when the engine runs, but the ZX swap scheme gives it power all the time.  I ran a wire over to the fuel pump power plug by the passenger seat to use the same power circuit as the pump, which only gets power during starting and engine running.

It's about as basic as relays get, if you did fry yours.  Any old relay should work.  The line from the alternator is the power wire that gets misdirected after the swap.  It actually comes through the VR.  Weird that the diagrams don't show it though.  This is the 1976 drawing.

Edited October 2, 2018 by Zed Head

[Dreamzz]

I opened the relay to verify. It appears crispy. Then with car idling and with brake light relay plugged in with the new fused 12v ignition switched source from added fuse block i pushed closed the relay contact and my brake light goes out. Let go and it comes back on.
Leads me to believe relay is bad or not actuating.

I may be wrong but I was under the understanding that the pre swap alternator source or the "N" output of the alternator drives the charge lamp and brake relay at less than 12 volts. Again I may be wrong but brake warning light relays in 76 are designed to actuate at less than full alternator output.

I don't want to pull power source from fuel pump which now also has its own new fused ignition source and is finally holding fuel pressure/fuel level in the triple carb set up I am now running.

I am thinking my solution would be a new relay capable of actuating with a full 12 volts without burning up. Was looking for some suggested relays like the one in this post.

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[Captain Obvious]

2 hours ago, Dreamzz said:

I may be wrong but I was under the understanding that the pre swap alternator source or the "N" output of the alternator drives the charge lamp and brake relay at less than 12 volts. Again I may be wrong but brake warning light relays in 76 are designed to actuate at less than full alternator output.

You are not wrong. In the original system, the brake check relay is designed to pull in at a voltage less than full alternator output. It is connected to the "N" terminal* of the alternator which should supply a voltage of alternator output divided by the square root of three, or approx. Alternator output / 1.73.

So I'm not surprised that your original relay went all crispy when you powered it from the full alternator output. Probably lasted for a little while, started to smell a little, and then went open circuit?

And yes... It sounds like a simple solution would be to use a relay that can handle the full alternator output (12-15 volts) on the coil all day long.

* For those who care, the "N" terminal is actually the neutral terminal from the three phase generator that is the alternator. And because of the three phase voltage, the L-L voltage is 1.73 times the L-N voltage. Conversely, the L-N voltage ("N" terminal) is L-L voltage divided by 1.73

[Zed Head]

1 hour ago, Dreamzz said:

I may be wrong but I was under the understanding that the pre swap alternator source or the "N" output of the alternator drives the charge lamp and brake relay at less than 12 volts. Again I may be wrong but brake warning light relays in 76 are designed to actuate at less than full alternator output.

I don't want to pull power source from fuel pump which now also has its own new fused ignition source and is finally holding fuel pressure/fuel level in the triple carb set up I am now running.

I am thinking my solution would be a new relay capable of actuating with a full 12 volts without burning up. Was looking for some suggested relays like the one in this post
 

Could be.  N enters the VR and probably serves multiple functions.  See attached, below.  CO knows more.  @Captain Obvious  Dang, looks like he's here... posting anyway!!!

Output is in amps.  At 12 volts or higher.  Amps do the damage.  My relay has been fine on the 14+ volts my alternator puts out on the fuel pump circuit.

Good luck.  The key is to have power to the control function of the relay only when the engine is running.  

 

[Zed Head]

N has a branch off to the relay.  It must get wired to battery voltage in the swap diagram.  Can't speak to what it's rated for, voltage-wise, or even what comes out on N.  Not my forte, and mine works.  Being lucky, I guess.

Anyway, many possibilities.

[SteveJ]

The neutral should be bonded to the ground. So it is at zero volts with respect to ground. If the neutral is not bonded, that can cause problems like a floating reference if the alternator is turning.

[Captain Obvious]

They didn't bond the neutral. The full alternator output is Line to Line in a 3-phase "Y" configuration and for normal stuff, you don't need it at all. Just run full wave rectification between all the L-L and the neutral is unnecessary for the 12V alternator output. One side of the six diodes becomes ground and the other becomes alternator output. No neutral needed.

However, they brought the neutral out to supply a couple things like the brake check relay and the voltage regulator. Not sure why they did that instead of just using the full output, but that's what they did. For some reason, they thought using Line to Neutral was a more reliable indication that the engine was running and the alternator was turning and working. Maybe it has to do with losing one phase or something?

Someone here with more 3-phase experience could maybe provide input?

How's that for a thread diversion?   

Edited October 3, 2018 by Captain Obvious

[SteveJ]

I misread the drawing that Zed Head attached. I need to get more sleep. 

I looked at the 76 wiring drawing to fill in details. The neutral goes to a coil in the VR in the 76. When the potential on the neutral is higher than ground, the associated contact moves the blue wire (lamp) from in contact with ground to the white wire (12VDC+) and lights the charging lamp. (Unless I have something backwards from looking at drawings when I'm tired.)

For the 74, the neutral goes to a coil in the VR and when the neutral has voltage with respect to ground, the associated contact grounds the black/yellow wire that goes to pin 12 on the Seatbelt Interlock unit.

For the 240 wiring diagrams, the VR is shown as a black box, so I don't have a ready description of what all it does in that application, though I think I have a 240Z VR lurking around unused in my garage.

 

[Zed Head]

Actually it "unlights" the brake warning lamp.  So the relay isn't as simple as I said previously.  It's a normally closed relay.  One of those 5 pin Bosch units, I think, would work.  Hundreds in the wrecking yards and eBay for cheap.

I remember some basic AC to DC conversion stuff, with rectifiers and wave forms getting their bottoms flipped over and all that, but learned it long ago and only 101 level and it's all corroded now, so I can't even make a guess on what N is doing here.

The relay in question sees 12 volts through the switch contacts, where the power comes through the lamp on its way to the relay, where it is grounded, and it sees N voltage through the relay coil which opens the circuit causing the lamp to go off.  The relay coils are what has crisped here.  Maybe my relay is living on borrowed time. 

Is there any way to tell what voltage a relay coil is rated to?  Marks, codes, etc.  The coils look just like the EFI and fuel pump relay coils.  Which get crispy also, over time.  The brake warning relay also tends to get wet since water pools in that area when there's a leak.  There are no drain holes.

 

[SteveJ]

Mea culpa. I misread the wiring at the lamp. Based upon Zed Head's last post I looked again and realized my mistake. I thought the lamp had blue & black wires going to it. (That in itself confused me some because with the 260Z, blue was usually a wire that became grounded.) Instead, the lamp has blue & green wires going to it. That makes sense since green is usually a positive. I stand corrected, even though I'm sitting down right now.

Now, I did a quick search, and I believe this link points me in the right direction. https://youronlinemechanic.com/alternator-with-neutral-point-voltage/

It says there is an AC component in the neutral voltage. You don't want to put a DC coil in an AC circuit...Er, I've heard that from a friend.

If the AC component is high enough, it might smoke a regular DC coil. A diode in the circuit might help.

This is all just speculating in this application. @Captain Obvious Maybe we should sneak over to my house during ZCON and hook my OScope up to the neutral and see what the waveform looks like.