Brake warning light on after alternator upgrade

[skunkteeth]

So I upgraded my alternator in my 280z to the 105amp from ZSpecialties. After installing it, the Brake warning light is constantly on. I presume this is from the T connector no longer being used. Which wire (white/black or yellow) should I hook back up? The white/black did nothing when hooked up, but when I hooked up the yellow to 12v the light went off then came back on. Is there a problem somewhere else in the Brake warning relay? It did not happen until the alternator was changed.

Thanks

[geoyam]

The yellow wire is connected to the brake warning lamp check relay. For a 1977 280z the yellow wire feeds 12 volts from the alternator when the car is started. This energizes the relay coil, thus breaking the ground circuit to the check lamp.

The lamp can stay on when the engine is started for several reasons; 1) parking brake is on or the parking brake switch is defective, 2) problem in the hydraulic brake system or the brake line pressure differential warning switch is defective, or 3) the brake warning lamp check relay is burnt out.

Based on the description of your problem it sounds like the relay coil is burnt out. Same thing happened to my 280z. The relay replacement part number is 25230-n4700. Unfortunately it is NLA from Nissan.

A replacement relay for model year 8/77 280z (25230-79906) was still available from Nissan but they are not interchangeable without some major modifications to the wiring harness or to the relay itself.

[Nissanman]

If you can post a diagram of what the relay configuration is, I'm sure we can adapt a conventional automotive relay to perform the function.

Nissan is/was notorious for using weird arse relay configs. and pinouts, I avoid using their relays like the plague.

If an over the shelf Bosch/Narva accessory relay will do it, it may be well worth fitting a conventional relay socket, especially since the OEM replacement is NLA:rolleyes:

[geoyam]

This is the diagram of the relay from page BE-35 of the 1977 FSM. The OEM relay is a SPST normally closed using only a 3 terminal connector. The terminal to ground is share by one leg of the coil and one leg of the lamp circuit. The second terminal is for the yellow wire from the alternator and the third terminal is for the green w/yellow stripe wire from the brake warning lamp.

If I remember correctly, you should be able to take a Bosch relay and wire terminal 85 to the yellow and terminal 86 to ground to power the relay coil. Terminal 30 is wired to the green w/yellow stripe. Terminal 87a should be normally closed and terminal 87 is normally open. You want to wire terminal 87a to ground and ternminal 87 is not used.

A Bosch relay socket can be used to wire into the factory harness. If you don't want to butcher up the harness you can wire the relay socket into a male 3 terminal connector if you can find one and plug the new relay setup into the factory female connector.

[Nissanman]

Here is a conventional SPDT relay config.

As mentioned, just correlate each terminal to the equivalent in the thumbnail and job done:)

relay.bmp

[skunkteeth]

WOW, tons of great info. When I get my car back from the mechanic (it might need a head rebuild) I will look into the relay and the parking brake switch itself.

Thanks a lot.

[sblake01]

The problem actually has to do with the elimination of the external regulator. That alternator is basically plug and play for the internally regulated cars (78 up) but not really on the 77 and earlier externally regulated ones. I have seen info on how to correct this problem without adding relays, etc. but I cant find it right now. Steve Golik (zcarnut on this forum) could point you in the right direction on that. He seems to be very knowlegable in this area.

[billyjarrell]

This is sort of on topic with this post so I'll ask here. I also recently replaced my alternator ( I also have a 77 280 ). I did a lot of research and found some great info about using an internally regulated alt. from a ZX. I bought the ZX alternator, followed the instructions for the 2 jumpers needed in the original regulator harness, and it worked great. But about 10 miles into my test drive the brake lamp relay under the pass. seat heated up and started to smoke! I disconnected the relay and everything else seems to work. anyone ever heard of this? I don't care if the BRAKE light doesn't work but I don't want to hurt anything else. Thanks, Billy.