Wiring question; Volt Gauge/Hazard

[rfaranda]

OK, here's what I've got:

Pos->Alternator resistance = .1

But the sense wire with car off ign set to on, I'm getting 12v at the connector.....

[Zed Head]

You got 12 volts on the S wire, which you should.

What did you get on the L wire?

[rfaranda]

You got 12 volts on the S wire, which you should.

What did you get on the L wire?

I mistyped, sorry.... Here's what I get:

At the B: 12.49v, S: 12.49v, L: 12v

[rfaranda]

More info... After tracing everything, I took the Volt gauge out, unplugged the t-connector at the alternator and I'm getting 12v at both points on the connector leadint to the charge lamp and the alternator... Also, when the t connector is unplugged and I turn the ignition to on, the fuel pump starts. It doesnt when the t connecter is attached...

I'm starting to get confused looking at the wiring diagram... :stupid:

[Zed Head]

I am not positive that the L terminal on a Nissan alternator will not take 12 volts. Your alternator may be okay. But I do know that the components of the internal regulator do not like current spikes (eg disconnecting the battery while the engine is running). You should probably take your alternator to an auto parts store and make sure it hasn't been damaged. You might be wasting your efforts on an alternator that will never charge.

For the record, I measured 2.5 volts on the L wire of a 1976 car that has been converted to internal regulation. Maybe 1978 is different but it seems like if your charge light is on and your brake check warning light relay is activated and your ignition relay (as shown by the diagram on EE-15), that you should not get 12 volts on that wire, when everything is connected. The charge lamp and relays should drop the voltage, leaving less than 12 at the L wire. So something is off, either my understanding or your PO's wiring.

[SteveJ]

Actually, let's take a step back. Rob, did you read the FSM? The Engine Electrical section that I referenced before has the diagnostics from EE-20 to EE-23. Perform those tests as described. It's a lot easier doing the right tests than to keep trying out our other suggestions.

[Zed Head]

I was wrong on when the ~ 3 volts or less are on the L wire. It is low voltage when the connector is plugged in, and the key is On. That completes the connection and lets the lights and relays drop the voltage. No current flow, no dropped voltage. I just checked on my car again. I had 12 V at the connector, unplugged, with the key On, and 1.8 V measured at the back of the plug when it was connected and key On.

Sorry about that.

Based on what you're written, unless your alternator is damaged it should be charging. You said that your charge light works (goes off when the engine runs) so that should mean that it is producing a charge. When your charge light goes out, that basically means that current is not flowing "from" the battery any more. So the fact that your charge light goes out must mean that you're getting some output.

I have read that using your alternator to charge a dead battery is very hard on it (another voltage spike situation). Something to be aware of.

SteveJ's suggestion to read the front and back of the EE section is good. I'll bow out now and avoid confusing things anymore.

[rfaranda]

Thanks guys. I actually have been reading the Fsm and did run their diags. I definitely have a better understanding of the charging system now.

I did get caught up on the L voltage today. Thanks for checking that out again Zed, I feel better about that.

At this point the circuit in the car seems to check out. I think I may have gotten a dud alternator. I'm gonna pull it and go have it checked/replaced.

Now on to the volt/hazard short.

Oh, and a little humor. I pulled the steering column apart to check the steering lock switch and was amazed at what I found. The previous owner apparently had an aftermarket cruise control installed. Seems the arm had broken off so they just tucked it into the column. I couldn't believe it!!!

Anyway, thanks for all the guidance.

Edited February 22, 2011 by rfaranda

[rfaranda]

Steve..... Just stepped through the hazard/volt gauge circuit.. My money was on the flasher but it wound up being the steering lock switch... Thanks for the help on that one.

Got the alternator out and taking her to get tested now...

[rfaranda]

Ok, now I'm royally confused..... The alternator tests fine...

It acting like my wife, it puts out but its not exciting. (I know, that was weak)

I'm at a loss. Everything at the alternator tests out....

[wa5ngp]

just fyi,

long time ago I was working around the alternator (engine was off) my wrench brushed against the +12 terminal. There was of course a huge spark and then the inductive kick. That inductive kick blew out the diodes on the alternator.:stupid:

So net is always remove -terminal to battery when fooling around in that area.

This was before lifetime warranties at AZ.

Don

[grantf]

This may sound to easy but have you checked the neg terminal at the starter for good contact or corrosion. I had trouble charging my battery two weeks ago and that was the fix.