brake warning light - relay bad

[Zed Head]

My burned EFI-Pump relay has a diode and a resistor in the circuitry.  A few more pictures of Dreamzz's burned relay might show something.

Maybe I'll pull mine out and take a look, to be sure it's not slow-cooking.

[SteveJ]

When diodes go bad, it isn't pretty.

[Captain Obvious]

Haha!!    Looks like something out of Tron.

He better be careful going out like that or he might get uhhh...  shot - key?

I'll be here all night, folks. Seriously. Where else am I gonna go?

[Dreamzz]

My burned EFI-Pump relay has a diode and a resistor in the circuitry.  A few more pictures of Dreamzz's burned relay might show something.
Maybe I'll pull mine out and take a look, to be sure it's not slow-cooking.

Finally got a chance to get back in the garage today. Thanks for everybody's input/posts. I am attaching some more photos of brake light check relay since mine is already opened and on the work bench.

Take notice of non insulated small wires from the inside terminals. I didn't even see these at first.
They attach from inside terminals to actual coil. From the underside main wire harness yellow and black are connected to these terminals with small non insulated wires. So from terminal fed by black wire you have small non insulated wire going to coil and then another small black wire going to top of actuator.
This is beyond my electrical knowledge but pictures may help in understanding.
I have ordered a new 12 VDC 5 pin relay and hope to install next week.




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[Dreamzz]

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.

 

Only marks , numbers, I found on the relay were on the outside case. See picture below maybe someone can decifer if they state rating of relay.


For now I have removed coil/relay and may just solder new relay to existing wires keeping relay inside original case and therfore keeping the original wire harness. I think it will fit inside original case. It would still look stock.



Now just have to figure out which wires to solder to which pins of new relay.

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[Zed Head]

Thanks for the pictures.  Looks like it's rated for 12 volts even if it's never supposed to see it.  And it just sends it to ground so nothing on the back side to drop current.

Heat, moisture, vibration, age...lot's of reasons for these old parts to fail.  You'll need the wiring diagram and the colors from the harness, I think, to figure out the circuits.  The wire colors on the components are often different than the harness.

Atlanticz has a 75 diagram but I just looked at it and it doesn't show the relay.  76 is probably your best shot.  Or just use a meter.  Two grounds, two powers, but only one power wire with the engine not running and the key on.

https://www.classiczcars.com/files/category/1-wiring-diagrams/

 

Edited October 9, 2018 by Zed Head