theandies

1971 Corvette ZZ4 350 MSD distributor and 6AL box.

I installed Daniel Sterns headlight relay kit about 2 months ago and ever since I get an intermittent high current draw indication (above the first tick mark on the ammeter and sometimes close to the +40 mark).

It never did this before the relay installation. Everything works great so I'm not sure why this would occur after the relays were installed.

I broke into the lamp harness to extract the headlight wires to wire the control side of the relays. I unwrapped the harness to the radiator core support so I know I didn't damage any other wires etc. I used the alternator ground as the ground for the low power side of the relays - I'm thinking of changing this.

On the high voltage side of the relays I tapped off the horn relay power (essentially the + output of the alternator) and the high power grounds are where the original lamp harness grounds are.

What is weird is sometimes the ammeter works as it did before the mod. Current draw just above the zero mark then goes up a little depending on what is turned on. Then other times I get the full draw indication described above. I get the normal high draw for a short period of time after starting when it is working "normally". Both these conditions remain for the duration of the drive either the high draw scenario or the before the headlight relay scenario.

I'm going to put my Fluke meters current probe on the alternator output this weekend to see if what the ammeter is showing is correct.
I'm also going to check the grounds again and check my battery cutoff switch (rotary **** style) and battery cables and battery ground. I'll also check the engine ground wire from the back of the starter to the frame.

Like I said, everything works, no magic smoke and the car will start after sitting for up to a week without needing a jump etc.
At this point I think either my battery is going or the alternator or alternator voltage regulator.

Any thoughts?

Vibguy

This happened to me on another car when I installed the relay. Before relay install, all current going in and out of the battery was indicated on the Ammeter (except of coarse the starter). After the relay install, the juice out of the battery would go directly from the hot side of the battery to the lights. So when the alternator kicks in to compensate for the voltage drop due to the lights, it would show the resulting positive current on the ammeter. I think it is normal. What current do you think your lights draw?

theandies

Thanks
This happens with the lights off. That is why I'm asking and it is what I am finding weird. With everything off except for the engine running I still can get this charging current indication.
The two low beam draw about 4.6 amps together and the two high beams draw about 7 amps together so total amps when all 4 are one is about 12 amps. That's with 14.6 volts (measurement verified after installing relays) at the lamps. Low beams are 35/35 watt Halogens, high beams 50 watt halogens.

Vibguy

Now I understand why you think it is odd. It sounds to me like a short then. Sorry I am not much help with vette specific short trouble shooting tips but with your DVM and a wiring diagram you probably can find it. What is the health of your battery? If you have another sitting around I might be tempted to start toubleshooting with that. Also take a good hard look at your ground strap. Folks don't usually think much about that ground strap but if you consider that all the electrons actually leave the (-) on their way around the car and return to the (+), then you can imagine how important that supply line is.

7T1vette

Sounds like a short to me, too. Any possibility of a diode gone bad in the alternator?

theandies

That was my first thought.
My wiring is good as I checked and rechecked it before hooking the battery back up after installing my relay upgrade.
I'm also leaning towards the battery too as it's coming up on 5 years old. All my grounds have been checked but I'm going to go through them again this weekend just to be sure.
As stated everything works fine and I've not released any magic smoke so all I can think of is grounds, battery or alternator and to asked here to see what others think.

theandies

UPDATE:
ALT output is a steady14.7 volts at the + lug on the back and also at the battery so I think my ALT is working good.
I checked all my forward harness grounds. Cleaned them and made sure I had good continuity to all of them from the back of the ALT ground lug. They are all very good now. Took it for a test run and the excessive charging indication was a little better but still a little weird. Got back home and checked my battery cutoff. Apparently I didn't tighten it completely down when I finished with my relay project. Tightened it down and went for another drive. This time the needle was a lot steadier than before but still showing close to the half-way tick mark. I'm going to take it out in a few once it cools down outside and test again.
Tomorrow I'm going for the battery ground and the engine ground. I think (hope) I'm on the right track.............

7T1vette

The diodes in the alternator may work fine, when it is turning. The question is whether they can block current flow when the alternator is NOT running.

sunflower 1972

Testing a GM CSI alternator: http://www.marinemechanic.com/site/GM_CSI_ALT.htm

george2066

what years run the ammeter? is the ammeter between the alternator and the battery(starter) and measures what the alternator is putting back into the battery? or is the ammeter between the fuse block feed and wherever that feed comes from (starter terminal again)

7T1vette

The ammeter does NOT measure full current flow; and the actual current flow does NOT pass through the ammeter. The ammeter circuit is a "shunt" design which actually measures a voltage drop over a section of the main [positive] power line in the car. The two leads from the ammeter tap into that same wire...but they are about 20" apart. Depending on the size of the wire and the amount of current flowing through it, the voltage will drop proportionally along the length of the wire.

So, GM used a measured length of the main power wire as a current shunt, and the ammeter is actually measuring the amount of voltage drop (millivolts), but the scale on the meter reads out as "amps". This method works fine, as long as you don't expect much accuracy [+/- 5 amps, or so]. And it also means that (unless something unusual happens with that wiring) very little current is actually flowing thru the ammeter.

C3's got an ammeter from '68 thru '76; in 1977 the ammeter was replaced by a voltmeter, which just measured the level of voltage in that main power line. If you know how to use an ammeter, it will give you more information about the electrical system than a voltmeter. But, most folks didn't know how to use it, so it didn't serve its intended purpose.

theandies

Didn't have any time this weekend other than what I've already checked. I was at my son's Lacrosse tournament all weekend. I'll have some time this weekend though. Thanks for all the info and please keep it coming if you think of anything else.

theandies

Update #2
I removed the battery cutoff and this seemed to make things worse as now the ammeter is pegged to the + side 99% of the time. I checked output voltage at the ALT stud and is between 13.5 to 14.2 volts. I connected my meter to the battery and went for a drive and the voltage is constant (between the two values above all the time).

This all began after I installed my relay kit for my headlights. I just can't see how that would cause this issue because it happens even with the headlights off but it's the only thing that was done electrically.
Here is how I wired my relays for reference:




The control side of the relays (from the headlight switch) grounds are to the ground stud of the ALT. The high power side grounds of the headlights are from the headlight plugs to the front harness ground location which have been inspected and cleaned. The power going to the headlights was taken off the ALT side of the horn relay.
Tomorrow (if it's not too hot) I'm going to go under the battery compartment and check the main battery ground and also the engine ground at the starter.

I checked the battery temp after driving home from work and it's not getting hot. The ALT was around 140 degrees using my IR temp gun but most everything in that area was that temp so I don't think it's getting "hot".

I did put a fire extinguisher in the car "just in case" as this is my daily driver right now.

7T1vette

Just curious: Why did you install 2 relays for the Hi-Beam lamps? Couldn't you just bundle all the wires going to the Hi-beams filaments (2 Hi bulbs and 2 Lo bulb high-beam filaments) and power them with one relay? They all come on together, don't they?

theandies

I was going to do that but when I received my relay kit from Daniel Stern it had 3 relays. I was confused so I talked to him and he said that is the way to wire it. It works well.

694speed350

Battery.

theandies

Going over the schematics the ammeter is wired on both sides to the horn relay. That is where I tapped power from for the power side of my headlight relays. I'm going to check those connections as well and may even rethink where I tap my power from.
I think it may be the battery too but I want to rule out all other things before springing for a battery that may or may not fix it. I'm thinking of taking the battery out of my son's car for troubleshooting tomorrow. Can't spend too much because my wife just gave me to go ahead to do the Fiero seat conversion I've been wanting to do for a while now.

theandies

I took all my power connections at the horn relay off and when I did I noticed on of the screws holding the power wires to my headlamp relays seemed a little loose. I got rid of the crappy fork style connectors from the factory wiring and put good ring terminals (and soldered) on them. I took all the slip-on connectors off the horn relay, de-pinned them and cleaned them up real good. Reinstalled everything and it seems to be good now. Benefit - my horn is louder now!!!!
Started the car and the ammeter went full charge but then drifted back to zero (zero as in less than a needle width from the zero tick mark which it's been like since I've owned the car) after a few seconds. I turned on everything and each time I turned on something the ammeter would jump slightly to the charge side then go back to zero.
I took it around the block and it stayed steady like before. I'll have to do some more road testing tomorrow for verification.

Thanks to everyone for your help. I hope it's back to normal.

theandies

I think it's good now. It had to be that slightly loose connection coupled with the old terminals. Thanks for everyone's help and if it comes back I'll reply to this thread again.

7T1vette

Your ammeter is now working exactly as it should...with a good battery. Anytime a high discharge occurs (after start, electric fan usage at idle condition, etc), the ammeter needle will immediately show the 'spike' of the current surge; then the alternator will respond to recharge the battery to a 'full' condition [needle moves back to zero mark]. If the rate of recovery becomes longer, it indicates that the battery can't be recharged as quickly. However, if the needle returns to the zero mark too quickly, it can indicate that the battery has little ability to take a recharge and needs replacement.

Proper "reading" of the ammeter takes some experience and background knowledge on how it should behave. I'm sure you can find lots of info on the web about how best to utilize an automotive ammeter.