Electrical gurus, wht am I missing?!?!?

[Jonboy]

I am still chasing electrical gremlins in my '79 SWB with the LT1. When I got the truck, it turned over a little slow, and it got to where it would not start. I had the battery checked, bad battery. I replaced it with a new Delco. The truck sits for the most part, so I have left the battery unhooked while I have been repairing the wiring harness, getting rid of a bunch of butt connectors. I have been soldering them one at a time, to make sure they are not getting crossed. Anyhow, I went to hook up the new battery, it barely turns over. I pulled the starter, and had it and the new battery tested. Starter good, battery bad. Battery showing 12.5V, 250 CCA.

I picked up another battery at work. Put it in, and the truck is slow to crank. It is showing 12.5 V at the alternator, battery, and starter with the engine off. Running it was showing 11.9. I pulled the alternator, and it tested good. Is it possible I have been getting bad batteries? (Keep in mind, the last one has maybe 2 minutes of running, 3 starts on it. Still tests 12.5 V with the truck off, will not turn the starter at all).

I am not really sure if this has been a problem, or I am just looking more now (after 3 batteries). I rechecked the cables for corrosion and to make sure they are tight, ground is good, ground strap from the cab to the engine, and from teh frame to the alternator case. I replaced teh ignition switch (the electrical switch) to make sure it is good, since I switched out the column. The gauge is showing 9-10 V (just above the red, below the 13V mark).

Is there something simple and I am just missing it? This has a 130 amp alternator, and no power accessories or radio. Shouldn't be a problem, I don't think.

[Driveway Dreams]

Not an electrical guru by any means but, Could the battery cable itself be bad? Inside the actual cable part?

[keith61760]

I am having similar problems in my 77. I just have a 350 and an alternator for a 90's engine. If I drive it everyday its fine for the most part but if it sits I have to jump it. Even with the cables disconnected.

I plan to do what Driveway dreams mentioned-Recheck my cables to make sure they are good and see if I can find something pulling power when it shouldn't. I am probably going to get a battery that can tolerate a load better than the one I have.

[qu1cks1lver56]

I'd replace the ground straps with something a little bigger, at least 4 gauge wire but I prefer 1/0.

And check the hot wires between the battery, starter, and alternator.

I recommend doing the big 3 under the hood on these trucks, the stock wiring they used just isn't very big.

you can check out how I did it in my build thread.

http://67-72chevytrucks.com/vboard/s...d.php?t=375526

I added an additional ground wire between the block and battery (making it a "big 4" i guess lol) and plan on replacing the hot wire to my starter soon, the stock wire has a low strand count and it's stiff and hard to work with.

I didn't check my idle voltage before I did it, but after it's 14.5-14.6

[joe231]

sounds like you need to check the voltage drop of your cables (let me know if you want me to explain how to do the check), and make sure you have adequate grounds.

[raveer2000]

Originally Posted by joe231

sounds like you need to check the voltage drop of your cables (let me know if you want me to explain how to do the check), and make sure you have adequate grounds.

I agree. A drop voltage test is in order for this one.

[Jonboy]

How do you do a voltage drop test? I measured it at the battery (12.5), at the starter (12.5) and the alternator (12.5). No real change in voltage.

When I took in the second battery, it measured 12.5V, and hardly any amps. My cables look OK, but I may pick up some new ones today, just to rule it out.

Are there any other tests I can do with a DVOM? If so, please explain them. I seem to remember just enough to be dangerous lately.

[joe231]

to check voltage drop will require 2 people unless you have alligator clips for your meter.
place one lead on the battery end of the hot cable, place the other lead on the starter end of the hot cable. With the meter set to read DC voltage turn your ignition key to the start position and observe the reading on the meter (it will only show with the circuit under load). Whatever voltage reads on the meter under load is the voltage you are losing through the cable (ie if the meter shows 10VDC then you are only getting 2.5VDC to the starter, the potential difference is 10VDC). Check your negative cable the same way. You want the reading as low as possible. Hopefully less than one volt on both cables.
If you need further explanation let me know.
I can also explain how it is possible to lose voltage through the cables.
I'm no expert, I just understand what I know about electricity

[Jonboy]

I have been sitting here today reading about these alternators (and auto electrics in general) until I am almost crosseyed. I think it might be wired up wrong at the regulator. That sounds about right. I think I am going to replace the cables out of self defense, but I need to rewire the plug on the alternator.

[78-5.3]

Originally Posted by Jonboy

I have been sitting here today reading about these alternators (and auto electrics in general) until I am almost crosseyed. I think it might be wired up wrong at the regulator. That sounds about right. I think I am going to replace the cables out of self defense, but I need to rewire the plug on the alternator.

i had a 88 crew cab with the same problem i took it to a friend and he ran a wire from somewhere to the altanator he said something about energizing ?? i think it from from the fuse box !! it was spose to be a quick fix but i never got the problem repaired ;it was a long time ago! i do remember i had to rev it when i started it it would go from 9v to 13.5 when i rev it ! strange!

[72lb4x4]

First, measure voltage directly across the circuit. In this case, the 2 battery terminals.

12.6V is normal on a good charged battery. If you're getting 12.5V it may be that the meter isn't exactly accurate. A no load voltage test on a battery doesn't indicate its good, just that its not necessarily bad.

A new battery isn't necessarily fully charged when you buy it. Its probably mostly charged.

Do you have a charger? I'd put the battery on a trickle charger for a few days and try again. Look into a battery tender if you aren't driving the truck regularly for a decent distance to keep it charged.

You say the voltage is down to 11.9V with the engine running. Not good. Try reving the engine to see if the voltage comes up above idle. You should get at least about 14.5V.

Quick tests for the big cables if the starter spins the engine slowly are to use one half of a set of jumper cables to connect the - battery terminal to the block, or the + to the starter and try to start.

Since the starter spins the engine, I wouldn't be too worried about the ignition switch or solenoid just yet.

[joe231]

13.5 VDC-14.5 VDC is an acceptable range for the alternator output, you don't want over 14.5 or you can fry a battery

[Jonboy]

I charged the battery most of the day yesterday, and put it in last night. Click. I am almost to the point of pulling the whole wiring harness, and starting over. It is messed up like a football bat.

If a (another, this one is almost new, but hacked up) new wiring harness wasn't $800, I would already have it here.

On the brighter side of things, the tech line at Painless Performance is top notch.

[69BBsuburban]

Sure sounds like a bad ground.
There are only 3 wires basically needed to crank over the engine....large gauge positive to starter, a good ground and the solenoid wire to kick in the starter. If it's cranking over slow, it's gotta be there somewhere....is the starter shimmed correctly?
A bad alt has no affect on cranking over the engine....

[Jonboy]

That is what I originally thought, too. Ground is tight, new bolt in the cable, cable end is clean. It is starting to just click. It is starting to seem like everything I do on it is making it worse. I am going to put jumper cables on it from the battery to the starter tonight, and see if that will help.

[joe231]

Where is you battery ground attached?
Make sure you have heavy ground straps/cables from the engine to the frame, from the engine to the body, and from the body to the frame.
The vast majority of electrical problems are caused by improper, missing, or inadaquate grounds.

[Jonboy]

It's grounded at the frame. I bit the bullet and went and picked up an Optima battery tonight. Off to the garage to see what kind of damage I can inflict tonight.

[72lb4x4]

The battery should be grounded to the engine since the starter is bolted to the engine and that's where the current is going.

How many batteries have you put in it? Seems like a lot. I hope you aren't paying for them.

[joe231]

yeah , you should ground the battery to the engine

[Jonboy]

It's amazing what happens when you put in a good battery. I rewired the alternator correctly, and put the new battery in. Charging at 14.6, 12.5 off. Rolled over like, well I don't know what, but it was easy, and starts with a bump of the key. I was really getting frustrated with all of this, and it's all because of crap batteries.

I work at a Chevy dealership, so getting the batteries wasn't hard, but it was getting old explaining that they were bad. I am taking the last one back tomorrow. I thought I was doing the right thing by getting Delco batteries, but I guess not.

I will move the ground from the frame to the engine tomorrow night. I am still impressed that it started.

[3r!c84]

well good job man

[joe231]

[qu1cks1lver56]

Nice man! Optima's are pretty good batteries. Did you get a red top or a yellow top?

[billnorman]

Let me be the devil's advocate. I'm glad your truck is going well finally, but the odds on this many bad batteries in a row are staggering. If you have any more trouble, get a post cleaner and clean the inside of the battery cables. If there is the right amount of corrosion there, the alternator will not charge the battery, but the battery will still try to start the motor. The thing that bothers me is the "click' that you had. This usually comes from the battery connecting to the solenoid, but the starter load killing the connection with a high amp load, usually caused by a bad connection or corrosion. Also, one of the worst things I've seen are the cheap replacement posts with the two 7/16th bolts to hold the cable in. They almost always go bad, besides they look like crap. If you can't afford new cables, get a large terminal lug crimped on the cable and use a marine cable end bolted to it.
Anyhow, I hope you have seen the end of your troubles, but the Optima is new, lets see if it works out in the long run.
I've seen bad cable to battery connections drop 6 to 8 volts under load. Keep us posted.

[Jonboy]

I went ahead and ordered new battery cables anyhow. The 95 Z28 cable has been discontinued from GM, but I found a suitable replacement (there are two large gauge wires made to the cable also). The positive cable didn't look too bad, but there was a little powder inside the terminal that might have got through the boot. I cleaned that up, but I have had a car that looked good at the terminal, but was corroded under the sheath a few inches from the terminal. The negative cable looked new, so I will just move the ground to the engine.

I am trying to make everything look as close to original as possible (not cobbled together), so using the aftermarket bolt on terminals and such won't work anyway. The biggest hurdle I have had is that this is my first "toy" in about 4 years. I had pretty much given everything away after my tools were stolen, and I moved. I had stashes of little stuff (screws, bolts, etc) that I need to replenish. I hate looking for stuff like that.