igende

OK would like to get some opinions on what may be going on here. 1988 V6 2.8L base firebird. Here is the back story. The car has been running fine, but recently I noticed at idle if I turn on any auxiliary electronics, headlight, rear defrost, blower motor (any one of these by themselves or all together) the amp indicator would drop down low, not enough to stall nor cause any noticeable change in response in the car. Upon acceleration she'd move back to the center and again at idle she'd drop. If those auxiliary items were off the amps indicator would sit in the middle. I figure it's a tired alternator.

I decided I wanted an OEM AC Delco so I went to their website and found two that are recommended for my car (100 amps and a 105 amp) Since they don't sell parts directly and there are no resellers in in my area, I went to Amazon looked up the part and ordered the 105 amp (website confirms it fits my car.) I removed the old alt and hooked up the new one. It's really impossible to hook up incorrectly. There is an electrical connector that snaps on in only one direction and then there is the cable from the positive battery terminal that connects the alternator, it fits over a bolt stamped bat and you tighten it down with a nut. That's it for electrical connectors. There are 3 bolts that bolt it in place.
I had removed the negative battery cable at the start of this procedure. Once the alternator was installed I reconnected the negative battery terminal.

My son started the car and within a few seconds the car cut off and he was about to restart it but noticed smoke. The cable to the battery started to melt the outer plastic guard that it runs through and the cable got so hot that plastic wire tunnel that it runs through started to melt and catch fire, this is with the car off and the key out of the ignition. I managed to disconnect the negative battery cable and put out the the small plastic fire. Now i'm trying to figure what happened? I took both alternators to autozone to have them tested. The new alternator passed their test. The old one (original one in the car) failed. The cable from the alternator to the battery is totally fried and needs to be replaced now It's actually a two part cable, it runs from the alternator to a junction on the body where two other red cables come off of that junction and then there is one black cable that runs from that junction to the positive on the battery. Interestingly the two red cables at the junction box look fine, but both of the black cables got fried (alternator to junction/junction to battery).

Before I replace them and put on another alternator I'm wondering where I should start to diagnose this. (Of course I'm worried i've now fried other sensors and electrical items, but we'll see.) I went to the dealer and they looked up the alternator and said this was the right one, but other than a difference of 5 amps they could not tell me what the real difference between the two recommended alternators were. Even though this is one of two listed might it be for a different type of firebird setup and be the cause of this issue? If the alternator is good and there is a ground somewhere that caused this why would it not have occurred with the previous alternator?

Thoughts? And thanks in advance for your review.

bigal55

iTrader: (1)

What condition is your battery in? Have it tested or if "old", just replace it along with the aforementioned cables. Make sure ALL your connections are clean and tight. Your cables/connections may have been bad which would cause a high resistance. With the new alternator providing a lot of current to try charge a low/dead battery and the high resistance, it is easy to create enough heat to melt the insulation. Before hooking the negative cable back up to the fully charged battery, use an ohm meter and check for a short or low resistance reading to ground. Using the ground cable as the ground point (do a second check using the engine block for ground point), probe the alternator BAT terminal, the junction block and then the positive battery cable/terminal. If all looks good, connect the ground cable to the battery and start the car, check to see if everything is ok as far as the alternator charging. GL! and HTH!

igende

The battery is a year old this month, a sears die hard. Prior to ordering the alternator I tested the battery and was getting a 12.4 volts reading so it's good. With the car running the old alternator was putting out 14.6, but when i turned on the headlights it dropped to 12.4 so it was bad. Beyond that testing electricity is a bit of magic too me, i know a little. When you say use an ohm meter and check for a short or low resistance reading to ground using the ground cable as the ground point as i touch each location, bat on alternator, junction etc should I get a continuity reading or no continuity if things are good?

igende

so after a quick google search on continuity (hopefully similar test with which you described) i did the following. probed the negative cable while disconnected from battery and touched it to it's own small grounding cable that goes to the body and got a beep, but i don't get one if i touch the actual screw that attaches it to the body. Then I touched a probe to the negative cable and touched it to the junction box/post/screw and did not get a beep. alternator and battery are currently outside of the car so i have not yet tested the pos battery nor the BAT terminal to the negative cable, but I did also probe the alternator itself by touching the BAT terminal to the housing of the alternator and did not get a beep. I've read that if you do get a beep in this case, that would be bad (there should not be continuity from the BAT terminal to it's own housing.)

igende

The battery cable that runs from the alternator to the junction box. Anyone know where I can order one? I've not found one on line and not sure what gauge wire it is.

igende

OK looks like 6 gauge for 60-100 amps and 4 gauge for 100-150 amps.

84 1LE

iTrader: (9)

Junc box/BAT terminal on the alternator is pos & housing is neg, so yes.You should'nt get a beep when you "touch" both. Melted wire means something is shorted, so id trace that melted cable.Something is seriously shorting somewhere.

igende

Thanks guys. I removed that crispy cable completely. I don't understand why it appeared to continue to cook after i turned off the car (maybe it was just the plastic burning at that point but it really did appear to continue to receive power until i disconnected the neg terminal because at that point the smoke began to subside.) I had another alternator on there that while it was running weak was still putting out necessary amps and I never saw anything like this.I ordered a new acdelco cable positive to starter and battery to terminal, but i don't think it includes the alternator to terminal wire and i've not been able to figure out where to get it. I don't want to get one from a junk yard given it maybe just as worn out. If anyone knows where to get one let me know. The acdelco I ordered so far is part # 2SX78 which is OEM. The new updated line looks to be built much cheaper. By the way 84 1LE if that is a picture of your ride it's awesome.

QwkTrip

iTrader: (22)

You witnessed a battery short to ground. Now you know what it looks like. Smaller gauge wires tend to burn open (like a fuse) and it is all done when the circuit is broken, but larger gauge wires hold up long enough for the insulation to overheat and catch fire and then the whole car burns in a fire. Very fortunate you were there when it happened. You were smart to disconnect the battery.


Electrical shorts like that are usually easy to find. It only burns the cable between the power source (battery) and the location of the short. Follow the wire to the end where the damage stops and you found where it shorted.

igende

Finally got around to hooking up the new battery cable. First I had the battery tested and it's good, I had the starter tested and it's good. I'm waiting for a replacement/new alternator, but I hooked up the old bad one so I could run some tests. I replaced the battery wire and the alternator cable. I looked around for other burnt wires and didn't find anything thank goodness. I cleaned up some connectors and reconnected everything. With the positive connected to the battery and the negative cable disconnected I touched the negative post and then touched the negative connector and got a continuity beep then did the same to the alternator post and got a beep, so thee is still a short somewhere. I'm going to start pulling fuses one by one to see if I can isolate a particular circuit and will report back.

bigal55

iTrader: (1)

As Qwik Trip said, your cables from the battery to the junction block and from the junction block to the alternator were the ones to burn, therefore, that is the path of current to ground. Disconnect your bat lead from the alternator and see if you still have continuity from that lead to ground. A continuity tester will beep when the resistance in the circuit being tested is lower than the threshold of the tester. Be careful as a light bulb may make your tester beep. This is why an ohm meter is the instrument of choice for this type of testing, it can differentiate between a light bulb (maybe 3 ohms) and a dead short (0.0 ohms or very close to 0). If you had a short between the battery and some circuit run through a fuse, the fuse would blow. If the short is between the battery and the fuse, pulling the fuse is not going to show you anything. I would start where the wires melted and go from there. HTH!

bigal55

iTrader: (1)

Some added info: When doing continuity tests, you don't need the battery connected at all. You are looking for a short to ground so the negative terminal should be your reference point. With your tester connected to the negative battery cable, probe the alternator bat terminal with the testers other lead. If you get a beep, it says you have continuity between ground (your reference point) and the positive battery lead(s). As stated, disconnect the bat lead from the alternator and probe the lead with the tester. Still get a beep? Go to the junction block and disconnect all the red battery leads. Test each lead individually to see which if any beep. Post your results. GL!

igende

Thx! Will do.

igende

Not sure what to make of this, no battery connected, while touching the negative battery cable I touched the battery post on alternator with the alternator cable connected and did not get a beep, then I disconnected the alternator cable and touched it with negative cable connected and did not get a beep, then I touched the junction box and initially got a week almost beep but could not reproduce that, all subsequent attempts at touching the junction box do not reproduce a beep. I touched the alternator housing to negative cable and get a steady beep, I can reproduce this each time, I believe this is normal? If I touch the bracket holding the alternator I do not get a beep but if I touch the bolts that hold the bracket in place I sometimes can get a slight beep, but cannot reproduce that consistently, probably because they touch the alternator housing? (FYI, this is the old original failing alternator that I'm using and reinstalled, I returned the new one I had the melt down with even though it tested good because I noticed a slight dent on the pulley. A new alternator arrives today.)

One thing I remembered, this car has AC, but it does not work. There are two plugs to it, one is connected, but the other has never been connected in fact that second plug which goes to the top front of the compressor was always hanging loose and that plug has always been burned/melted. I looked for it and found it stuck between the brake fluid reservoir. I removed it from there and tried to ground it to metal in several ways to see if that might cause a beep at the alternator post to occur, but no luck. That might be a rat hole but wondering if it was the source of the issue. No matter what I do now I can't reproduce a beep showing continuity other than what I've noted above. Also if I touch the neg cable to the back of the ac compressor I get a beep, i'm guessing that is normal like with the alternator housing, but not sure.

I also tried doing the same tests but instead of touching the negative cable, I tried touching several places on the engine, but got same results as above. I did at one point jiggle the ground cable that goes from the back of the engine housing to the firewall just to check that it was connected and it is, not sure if jiggling that had any effect on anything. I appreciate any feedback you can provide. Thx!

bigal55

iTrader: (1)

This is all "normal" as your touching anything that is at ground potential gave you a beep. Your brackets are all grounded to the engine and thus should get a beep when checking to ground for continuity. The positive battery leads at the junction block and at the alternator should not beep (which they didn't), so that is good. Paint, corrosion or just a loose connection can cause high resistance at a joint so you may not get a beep when you should, take note of this! This leads back to the "new" alternator, it was probably the culprit as evidenced by the alternator wire being the ones that burned. When attaching the battery lead to the alternator "bat" post, be careful not to over tighten or turn the stud in the alternator. Good luck with the new alternator install and if you need any more assistance, I will be following this. HTH!

igende

OK thank you. Once I hook up the new alternator I will retest see if same results as just now prior to final connection of the neg cable and will let u know. Thx again.

igende

OK new alternator came in and I installed it. With the negative battery disconnected I touched it to the battery post on the alternator and I get no beep, I touched it to the junction box and I get no beep. I then touched it to the alternator itself and as before I got a beep which is expected, I noticed when touching to the housing that along with the beep I got a reading on the multimeter which had previously been at 0L, it has an ohm sign on the display so I guess it's showing ohms, it jumped to 59 and then slowly dropped from there down to 2.5 where it hovered. I tested this several times and each time it would start at about 50 or 60 and drop some times under 1, one time it jumped when I first touched it to as high as 135 (only once) and dropped to under 1. Given it's suppose to beep when negative to alternator housing, do those readings mean anything (resistance) and should I be concerned at all?

bigal55

iTrader: (1)

I wouldn't worry about the readings you got when touching the alternator case, it is supposed to be grounded. The ohm readings you see are due to things like corrosion or paint between contact surfaces. Ideally, anything that is directly bolted to the engine should have no resistance to ground (0 ohms). It is good that you don't have a low resistance reading from the bat terminal on the alternator to ground. You should be good to connect the negative battery cable up. If there are no large sparks when connecting the negative cable to the battery, you should be fine. You will get a small spark due to the small amount of current being drawn by things like the ECM, radio and maybe a clock or some other devices that are always powered. GL!

igende

Hey before I hook this think back up I have a question. When I first tested for continuity after replacing the cables I had gotten a beep which later I could not reproduce, today I ran a few more tests and found that If I touch the black lead which is connected to the com on my multimeter to the negative cable which is unhooked and the red lead to the BAT terminal on the alternator the display is 0L and I get no beep, however if I do this same test, but touch the red lead to the neg cable and the black lead to the BAT terminal on the alternator I get a constant beep and continuity is 0.00. Any idea why this would be the case? I can reproduce this consistently and I thought it should not matter what lead you test with.

bigal55

iTrader: (1)

That would actually be a good sign. You are reading the diode trio in the alternator. A diode is like a check valve for electricity and will only flow current in one direction, this is how the alternator turns ac current (bi-directional) into dc current (one direction). The current needs to flow from the alternator to the battery and not the opposite way. I believe this was the problem with your first "new" alternator. If the diode trio is shorted, it will allow battery current directly back to the alternator coil (very low resistance ) and create a high current situation (witness the melted wires). Your multi-meter produces a small voltage across the test leads. When the leads are touched together it creates a short and your meter reads this as 0 ohms. When there is a resistance in the path between the test leads, the current is reduced and the meter reads that as XX.XX ohms. Depending on how you orient the test leads, the diode trio in the alternator will either allow current flow (00.0 ohms) or will block current flow (OL). FYI, OL stands for Over Load which means the reading is beyond the range of the meters capability. HTH!

igende

OK thanks, looks to be all normal, I hooked up the alternator cable and started the car, it ran fine. I looked for smoke and initially saw some coming from below the alternator, but I think it's just the exhaust burning off some of the fire retardant I had sprayed during the initial fiasco as that smoke has since slowed and appears to have stopped (or maybe residual oil on the alternator from shipping.) Either way I drove her backwards a few feet let her run for 5 minutes and shut her off. Touched the cable and they are cool to the touch. I think I'm OK now. I need to replace some conduit and and tighten some wires down solid before I take her for a real run.

One question if you have time, like a moron I forgot to hook up the alternator connector when I first started it but she turned on and ran fine, I noticed this, stopped the car and plugged it in, I'm surprised it ran, thoughts? (with all the issues you'd think I'd be more careful, but tired I guess.) Curious about your thoughts on running the alternator with out the connector connected, I can't believe I did that, might have risked more damage, duh.

Thanks for all your help, you have been once again fantastic and a life saver, can't thank you enough!

bigal55

iTrader: (1)

Nope, no problem. The alternator was not "excited" therefore just turned without really doing anything. Should be good to go! Glad you got it straightened out and glad I could be of help!