HELP! HELP!

[Marc N.]

I HAVE A 1970 454/390 BB IN MINT CONDITION. I AM HAVING A PROBLEM WITH A GAUGE OR I THINK IT IS THE GAUGE BUT NOT SURE. WHEN I START THE CAR AND THE ENGINE IS RUNNING, MY AMMETER IS DISCHARGING AND ALL THE WAY ON -40. IF I PULL THE LIGHT SWITCH OUT AND IN FAST, I CAN GET THE NEEDLE TO GO STRAIGHT UP, "O". YET IS SLOWLY GOES BACK TO DISCHARGING AT -40. WHEN I DRIVE THE CAR AND IT GETS WARMED UP, IF I DO THAT TRICK WITH THE LIGHT SWITCH OR EVEN PLAY WITH THE POWER WINDOW SWITCH, IT COMES BACK TO STRAIGHT UP FASTER AND EVEN STAYS THERE LONGER YET SLOWLY GOES TO DISCHARGE EVENTUALLY. THE BATTERY IS FULLY CHARGED AND CHECKED, I THINK IT MIGHT BE THE ALTERNATOR BUT I CHECKED THE CONNECTIONS BUT IT SEEMS OK. IF IT SHOWS A DISCHARGE, DOESNT THAT MEAN A SHORT. HOW AND WHAT DO I CHECK FOR AND CAN THIS CAUSE A FIRE OR WHAT IS THE WORST THING THAT CAN HAPPEN. TELL ME WHAT TO DO AND I WILL FOLLOW ALL LEADS

HELP AND THANKS TO ALL MY NCRS MEMBERS

[Chuck G.]

Re: HELP! HELP!

Hi Mark; I'm no electrical expert, but if you're showing a discharge, and the needle never gets into the charge (+) range, I would guess that your alternator is bad. It wouldn't be that difficult to remove the alternator and take it to a local electrical shop to have it checked out. Hope this helps. Others might offer further thoughts. Chuck Gongloff

[G B.]

I can understand why you're shouting

A 40 amp current draw is more than any of your fused circuits is designed to take. In fact, it's more of a discharge than you would have if you were running your car without an alternator at all with the fan blowing full speed and the high beam headlights on.

I suspect a poor electrical connection somewhere. If it really is a ground with a 40 amp draw, you should find it before it fries the wire. Believe me, you don't want to locate it by using the ol' smoke test while driving.

[Wayne]

Re: HELP! HELP!

There's a good chance its a short in the alternator.... remove it and take it to an electrical shop for a checkup before looking further.

[Jack H.]

Re: HELP! HELP!

Marc, I am an electrical engineer. Let's see what we can. But, first your posts in all capital letters indicate you're SHOUTING at us. That's a minor piece of 'netiquete'.

Let's see, you say you've got a '70 BB. OK. The purpose of the alternator and it's internal solid state voltage regulator is to pump DC current into the battery to replace what's been lost. Your ammeter reads erratically. The first question is: is the ammeter telling you 'funny' stuff or is it right? The second question is whether or not the system is charging properly. Then, you move on to what's wrong where and it might be more than one thing gone wrong....

I'd start by putting a voltmeter across the battery itself. With the car off, you should see something in the range of 12-13 VDC because each cell typically has a potential of 2.2 volts. If the battery is run down, it'll read below 12V saying there's a problem.

Now, start the car. The alternator's internal voltage regulator should sense it's output is above the battery's DC level, connect the alternator into battery charge mode and begin supplying current to pump up/restore the battery's charge. If this is working, the voltmeter across your main battery will jump from what it read with the engine/ignition off to being in the 14-17 VDC range. If it does and remains rather stable, then the charging system IS WORKING and you can start looking elsewhere for your 'funnies'.

If the voltmeter doesn't come up to this range or it wanders/jumps around, you've got a bona fide charging problem. The advice of having a pro check out your car isn't bad (Mr. Goodwrench is STILL in business). But, some guys will remove the alternator and take it into a parts store where there's an alternator test jig. This can mislead you!

If the alternator's fried dead solid, the shop bench test works real good. If you've got flakey electrical connections in your car, you just left 'em behind and they aren't being tested! If you've got problems that are a result of intermittent nature (heat, vibration, belt slip), the bench tester at the parts store will only help you to the degree of it's sophistication. Few of these 'go/no-go' testers run an alternator very long, place a sufficient dynamic load on it, nor pace it through its dynamic RPM range.

On these early Shark cars, I can tell you two good/quick places to look for common intermittent problems. Both deal with the alternator's built-in voltage regulator. Earlier Corvettes (Mid-year, first Shark) used 'dumb' alternators with the voltage regulator in a separate external box. By '69/70 the alternator's control electronics started moving inside to save money and space.

The alternator will only do what it's told (charge or not/how hard). If the controller system (voltage regulator) isn't working OR isn't seeing the right inputs, the symptoms you describe can/do result. Now, the voltage regulator senses or 'samples' the car's battery voltage to determine when it should charge, how long, how hard. What if it's not 'seeing' the true battery voltage? It'll act 'wierd'....

Your verison of the Delcotron has a split sense path. Later alternators went to a single sense wire configuration with less to break/go wrong. Your alternator 'senses' battery voltage by way of a two conductor plastic side terminal plug. The side terminal plug has a pretty good reputation for mechanical fatique at it's internal connector crimps. Every time you connect/disconnect this plug you bend the wires and can loose contact integrity due to mechanical fracture/fatigue. Look at 'em REAL CLOSE, if they're worn get 'em fixed for good/solid contact.

Next, the sense wires feed into the car's wiring harness and 'go places'. One of the places they go is the engine compartment's common B+ bus. That's the two screws on the side of your horn relay. Be careful! This location is ALWAYS HOT regardless of the position of your ignition key!!!

If your work here, be careful and DISCONNECT the battery (either lead will do) like the Chassis Service Manual says to do. There are a number of wires connected to the two screw terminal on the side of the horn relay. They supply power to various circuits and do different things, but one of these wires is a prime part of your alternator's voltage regulator sense circuit.

These wires can also wiggle and fatigue over time. Also, the contact screw can be loose, AND you can have high corrosion/poor contact along this surface. Check to see that everything is clean, tight, and ship shape.

Last, if the alternator's sense circuit is being 'teased' by bad ohmic contact, it's a race. Who's going to blow first? The bad/sloppy contact wire or the alternator's internal charge control circuitry that's hearing 'give me charge', 'no, turn it off'....

Good luck!

[Tom Buddie]

Beam Me Up

Did this car just all-of-a-sudden start doing this? Or, did it start doing it after someone disassembled & re-assembled the ammeter? Does your battery stay charged? If so, the leads on the ammeter may just be reversed. Otherwise, all of the other posts's have it pretty much covered.