I was left stranded last Sunday with a dead battery, which is 1 month old. When car is running I unhooked negative side of battery terminal and car shuts off. I am thinking car should run off alt.

8 hours ago, jlenownnab said:

I was left stranded last Sunday with a dead battery, which is 1 month old. When car is running I unhooked negative side of battery terminal and car shuts off. I am thinking car should run off alt.

I may have missed it some where, but does the car have an amp meter or a voltmeter, and if so was it not showing discharge or low voltage before the car left you stranded? If it has an amp meter you should see it swing into the charging side right after startup at least for a min or two to recharge the battery from the starting process. If it has the voltmeter the voltage should go up after starting and I think it has a charging light that will tell if its charging or not (76 is when the amp meter went away in favor of the voltmeter/charge light).

The best way to confirm charging if for some reason the amp meter or volt meter is not working would be to use a digital voltmeter (40$ at a lowe/homedepot/habor freight/radioshack) and measure the voltage at the battery terminal with the car off, then start the car and see if the voltage comes up, rev the engine some and keep checking. Besides the alt not working if your amp/volt gauge is not telling you about the issue then you have that system to look into as well. At a minimum you should be able to check the amp/volt gauge by just turning on the headlight with the car off, look for a discharge if amp or a drop in voltage if a voltmeter.

 

Edited July 2, 20168 yr by Dave WM

I have an amp meter it does work I was not looking at it that day I wasn't planning on to break down

If the amp meter is working and not showing charging then the 1st thing I would do is the power up to the F term to see if the alt will work with that VR bypassed (two prog plug out, jump lead from F to BAT).

If that does it, then check for voltage at the N connector, should be about 6v (with the car running) You can also ohm out that N to ground should be a resistance there, not open but not low this is also in the FSM pic that Zed H attached.

If that checks then I would suspect the VR charging relay is not latching completing the charge circuit. If you tried a new VR then I would suspect the wiring from the N term on the alt back to the round connector for the VR.

 

Edited July 2, 20168 yr by Dave WM

Also on some cars it is a bad idea to disconnect the battery while the car is running. That alone can damage the alternator...

Finally and ending!

On our second pass through checking the fuses with a meter or something, I asked my guy if there were any missing, he said just one.... I asked which one? He said the fuel gauge, caliberado, the third one from the top left. That's the one! That fuse works the tach, fuel gauge and the whole alt, vr thing. 13.6 finally. thanks everyone for helping.

That's the IGN I beleive, 20 amp.

What the hell is a caliberado? Curious on that, not familiar with the word. Me speakie no spanish.

Site had it in two posts, first page.  Damn.  Not sure why the fuel gauge fuse would power the VR though.  Maybe the wire wiggling helped out.

This is from the 1976 FSM.

 

I think that IGN is actually the fusible link that supplies those fuses.  Just realized something.  IGN, ACC, HL, and the main link (BAT).  Not sure what ST is doing there though.

I was going off my 240. When I had a bad alternator in there it popped that fuse as soon as I turned the key. I read it was back charging through the ignition circuit and burning that fuse. On a 240 it's a single 20 amp fuse.

Glad you fixed it. 8^)

Is there an upgrade fuse panel like on the 240 or is this not a problematic area usually?

It's not a problem with the fuses, I had a bad alternator.  I like the 280 fuse panel better than the 240, more fuses that single out more circuits.  When that one fuse blew on my 240 it killed just about everything the key activates.  Your's will be fine now that it has a fuse in there.

The fusible links in the engine bay is a whole other story.  Lot's of people upgrade those.  You can't buy one at the local 7-11 when they melt.