the rear of the passengerside cyc. head is grounded to the fire wall...as well as the main wiring harness....to the fire wall....when you put a meter to the positive on the alternator....was the wire still on....try taking the wire off and using only a meter....then you isolate it to just be the alternator...if its good...then.one by one disconect things as you go from there....then you can track down and isolate the drain....if its not the alternator....something else is draining it down

 

I'm a little confused but appreciate the response. Are you asking if the cyl head and wiring harness were still grounded when I checked the alt? If so, the answer is "I assume so." I'll have to check those grounds to make sure they exist and look good.

When I tested the alt, I had the positive tester touching the output line of the alt and the negative tester grounded to the passenger side quarter panel. Sound good?

 

no thats not what I ment....I'm sorry,...what I ment was the 1 single + wire that goes to the output on the alternator disconected??...I was asking if it was removed..if so..it would be the same as a bench test....isolating the alternator all together...to make sure it works.......the other resopnse(ground wires on the fire wall) was simply answering your question on the idea of the car having more grounds than just the neg. battery cable....
I've seen many of these gm type alternators be bad straight off the shelf....if it works...then your down to tracing the wires....follow that positive wire off the alt...and use the meter, the point where that wire meets others near the battery on a lug(black plastic thing mounted usually between battery and radiator with several positive wires under the nut on the lug) is a good place to start

 

Ahhhhh! I see. I thought it was a bit odd to try and test the system with the grounds disconnected!

I did test it with the positive cable running off of the alternator to the battery. So, you're saying to disconnect that cable, then touch the tester to the output of the alt and check that reading. Gotcha. I'll try that.

 

yep....
let me know what you see....

 

I didn't have time to look at the alternator voltage this past weekend, but I was just flipping through my Haynes manual and looking at the electrical diagram for the charging system.

What's the deal with fusible links? Can they fail, break, die? How would I diagnose that?

 

Check alternator output with the positive on the output stud, negative on the alternator case. If it's still low, could be bad alternator. Could also be the excitor voltage. On a lot of GMs, excitor voltage gets fed into the back of the alternator. On older models, the voltage came off the ignition switch, thru the generator lamp on the dash, then to the alternator. If this voltage isn't present, alternator never charges.


I don't know if 86s use excitor wire, but I do know alternators for 3rd gens are crap. I replaced 4 in the few years I had my 89 Formula 350. Good thing I got a lifetime warranty when I got the 1st one from AZ. Take the alternator off and have it checked, if it's good, suspect your wiring/grounds.

To see if you've blown a fusible link, you need to use the ohms function on a multimeter (disconnect battery for ohms checks). This checks resistance. Fusible links (fuses too) are basically thin wires that burn up when too much current passes thru them. When they are good, they should read low ohms when you measure across them. If they are popped (open) they will read mega ohms.

I don't think your fusible link is open, reason being you read same voltage at battery and at alternator. If link was open, your readings would have differed significantly. With meter negative on battery -, you should read higher voltage at the alternator stud than battery + if alternator is charging. There should be a small difference in voltage (.2 -.4 volts) between stud and B+. If there is more, you have excess resistance in the output wire from alternator to the B+.

As stated previously, alternators can be bad off the shelf, so until you have it tested, you can't rely on it to be good. Also be sure to check where the battery negative cable grounds on the block, paint or rust under there can cause all sorts of problems.

 

Great info, thanks. I'll be working on the car this weekend and will test that stuff out.

 

I know this may sound completely insane, but sometimes we over look the simplest things.

Make sure your belt is tight and your alternator is running at 100% I had a car run hot and the alt wasn't chaging correctly. I changed everything chasing that problem, even the radiator. Then one day kicked myself in the butt cause it turned out to be nothing more then a loose belt.

I know it sounds crazy just a heads up.

 

Thanks godspeed. I'll take any advice I can get.

The belt is snug. I've been swapping in the new and old alternator while replacing wires, each time I have snugged it up good. When it wasn't, the belt whined real bad, so I'm sure.

I think my biggest concern is the wiring. I've still got to test the new alternator, just been busy and haven't had time to get to the car. The engine was rebuilt about 80k miles ago and between that and the aftermarket carb, I have some... unique... wiring by the looks of things.

For example, the fusible link to on the cable that connects the + output of the alt to the + battery terminal is rigged up. The brown/red wire that runs from there to (I think) the dash gauge used to run out of the link, ut is now clipped off at that point and runs out of a splice done on the wire between the alt output and the link. That concerns me a bit.

 

take the power wire that goes from the ignition to the altenator.splice it..run it to the battery..leave other wires connected into alt.mine was doing the same..it works..number 2 pin..i think its called..but there is only 2 comming outta the connector on top..just run it to the battery.off the plastic clip

 

So I had a fresh look at the work I've done so far. I noticed something that's probably an area of concern: in my re-wiring of things, I have (inadvertently) removed the fusible link between the alternator and the battery. Is that gonna be bad?

When I replaced the positive battery cable, there was a lot of corrosion on the wire right after the fusible link before it hooks into the positive terminal of the battery. The only way to clip off the old wire was to clip it *before* the fusible link.

Do I need to buy a new alternator to positive battery terminal cable with a fresh fusible link on it? Is the danger that, without the link, a surge could fry some components because the link isn't there to protect the system?

 

If you're still working on this problem do the following, or just take the car to a parts store and test the alternator and battery for free.

The Alternator testing procedure for my '88 reads:
Connect ammeter in series at alternator output BAT terminal, then connect voltmeter and carbon pile (pile puts a load) across battery terminal. Ensure battery is fully charged.

1. Operate engine at moderate speed. With carbon pile turned Off, check voltage across battery terminals.
2. If voltmeter reads above 16 volts, repair (CS-144 alternator series only) or replace alternator.
3. If voltmeter reads below 16 volts, proceed as follows:
4. With engine still running at moderate speed turn accessories On and load battery with carbon pile to obtain maximum amperage output. Maintain voltage above 13 volts.

If output is within 15 amps of rated output, alternator is satisfactory.
If output is not within 15 amps of rated output, alternator is defective and requires repair (CS-144 alternator series only) or replace alternator.

That fusable link should be for the fan(s.)


Good Luck and let use know if you fixed, or are just living with it.

 

Thanks for that tip.

I am still working the problem but the East Coast weather and my free time aren't cooperating on letting me fix it.

Can I ask you what the hell a carbon pile is???