adamhwong

I just bought my first Corvette - a 1985 coupe with the Z51 package. A week or so after I brought it home, I opened the door to find that the door lights didn't come on. I assumed it was a dead battery. Checked the records, turns out the battery is a bit over ten years old, so I buy a new battery, swap it out and problem solved.

A month later, I was a busy and couldn't drive it as much as I wanted to, it sat for about a week. Opened the door, no door lights again. Hmm. Must be a battery drain issue, okay, that's fine. I'll pull fuses once the battery is charged, etc. and figure out what the problem is.

I hook the battery up to a Deltran Battery Tender Junior and it immediately starts flashing green. Hmm. Instructions tell me that means the battery is charged at least 80%.

So once the battery is fully charged (it's charging now) I'm going to put it back in and see what happens. Has anyone experienced this before? Does this mean my Corvette needs to have near a full charge battery for it to be operational?

Also, obligatory first pictures attached

JrRifleCoach

Time to start checking for drains.
You'll need an ampmeter to detect where the drain is coming from.
Or just the the CTSY fuse and see if the batt holds a charge.

antfarmer2

I agree nice car!!!!!!!!

DinoBob

Nice, nice. Gorgeous early C4.

Please check all of the wires connected to the block behind the battery. This saved me from a potential fire.

WVZR-1

OP's car is an '85 and doesn't have the block you mentioned.

OP certainly needs to become familiar with procedures to do a "parasitic draw/load test" - there's so many variations of how to do it that it's likely best for the OP to GOOGLE, find one that he's comfortable with and follow that particular one.

A quick first check would be maybe if the car is garaged to go out at night and with doors shut, widow down, keys in pocket do a walk around peeking under the hood (without lifting) and under the rear bumper, in the window for maybe a courtesy light or even maybe a map light.... Listen closely also for maybe a "hint" also.

A fellow did a very good one here on the CF a while ago, I remember a yellow car and I'm quite sure his wife helped.

Paul Workman

Knowing how the system works, i.e., wiring schematics are essential for tracing problems. If you don't have one, then maybe someone here with an 84 can email photos of some pages from "the book". (Ultimately, having a Factory Service Manual (FSM) is essential for maintaining these older cars.)

You'll need an ammeter; a digital one with the capacity to measure up to a minimum of 10A (for short periods, at least).

If you're not familiar with using a (digital multi-meter or "DMM") configured to measure current, a word of caution here: 1) ALWAYS disconnect the meter from the circuit before re-configuring the meter connections for normal (voltage/resistance) tests. If you forget and say you try to take a voltage reading, you stand a good chance of at least "popping" a safety fuse inside the meter, or possibly destroying the meter!

Always configure the meter for measuring amperes before connecting the meter's leads in series with the load. Otherwise, there may well be some arching within the meter's function switch that could damage the meter.

If you know all this, then a starting place is to disconnect one of the batter terminals ( the RED positive is easiest and then connect the meter test leads between the battery and the disconnected battery cable; red lead to the positive battery post terminal and the black lead to the cable.

The 84 FSM may have some specific values for normal "keep-alive" current draw, but a good rule of thumb for the C4 is it takes about 0.025 to 0.030 A on the Amperage scale (most meters have a 10A scale), or 25 to 30mA in the milliampere (mA) scale. The actual draw may vary, depending on make/mo., but generally a draw above 50mA is cause for investigation. Certainly a draw of 1A or more is most definitely excessive.

If you have over 50mA, and certainly 1A+, watch the meter while you (or a helper) pulls the fuses, one at a time. When a fuse is removed and the EXCESSIVE current draw drops to hold at normal (or drops to zero), that is the circuit where the next step to isolate the problem begins.

You sound like someone familiar with troubleshooting electrical stuff. So, I guess I'll "park it" here and wait to hear back what you've found.

WVZR-1

OP needs help from an '85 FSM. An '84 is very similar but needs/helps to be correct year.

PatternDayTrader

I'm not 100% sure I understand the problem. Your interior lights don't illuminate or it wont crank over ?

Crash594

Just went through this with my 1990 I just purchased. Ended up being the alternator. Someone had unplugged the ctsy fuse and this caused other issues.

JrRifleCoach

There is also the problem with the insulation shrinking back from the connectors. This leaves about an inch of exposed copper wire that will become a problem when you start tugging on wires in the engine compartment.

Carry a fire extinguisher and battery cable cutters.

Hot Rod Roy

JRC, did you read post #5? Are you recommending "tugging on wires"? There must be a better way to find a loose connection! It sounds to me like the OP needs to check for good, clean ground connections. If the battery is truely at 80% charge, the interior lights would still work just fine! Time for some voltage drop tests and some clean ground connections!

Paul Workman

Thanks for pointing that out. My bad. Thought I read "84".

OP: Sorry for the year mix-up. But the procedures outlined remain valid regardless of model year. IF you determine you have excessive current draw, and you verify there are no courtesy lights or storage compartment lights running, pulling fuses is next. But, after that, you're going to need the 85 FSM or let the board know what circuit has the load so someone can post appropriate copies of the circuit(s) so you can divide and eliminate!

WVZR-1

I only pointed it out because there was the "check the battery jump block" also mentioned which he doesn't have.

I found the fellows C4 -video link and although I might do some things differently it's certainly a good start for any C4 owner with a suspected "parasitic draw". Easy to follow - good very short & informative for the DIY guy.

https://www.corvetteforum.com/forums...ube-video.html

exitwound

Put a multimeter between the +ve battery terminal and the lead and see what you get. With the courtesy lamps on it'll be about 4a.
Pull the ctsy 15a fuse and it should disappear.
The problem I had was traced to the light switch. With the fuse back in, sit in the car and watch the 4a vanish when the lights time out. If it doesn't, wind the light switch around and hopefully the 4a will go away. This worked for me and I sorted it out with a new light switch. The old one was somehow not lighting the ctsy lamps but taking the power anyway.

hcbph

Just found a battery drain myself last weekend. I found that the engine was electrically hot if you had the negative battery cable unhooked and touched a volt meter between the engine and the negative post of the battery. How i tracked it down was I used an OHM meter between the battery post and engine to confirm there was a circuit established. I pulled all the fuses one at a time, no luck. Then I realized what I thought were relays in the fuse panel were in fact circuit breakers. When I got to the one for the power locks and power seats, that one broke the circuit, no more juice though the engine.

I've yet to delve into it to track it down, I pulled the circuit breaker for the moment so I can still drive the car.

adamhwong

First report: battery isn't fully charged yet. Only holding at 11 volts.

So I'm not sure why the battery tender light was a solid green the first hour. It's solid red now, and it's been about 24 hours. Going to give the charge another day and then we'll see.

I installed the battery into the Corvette just to see. The lights/dash turn on when I turn the key to ON, but when I try to start it everything dies - lights/dash turn off, no crank.

Research tells me a battery tender junior should charge a dead battery in about 35-45 hours. I need to get my glasses adjusted because I thought it'd be done in 6-8 hours

Hot Rod Roy

Please don't hijack the OP's problem. You need to start your own new thread to get answers to your questions. Hint: You're off base in your investigation.

Paul Workman

I appreciate the technique you describe, but only in isolated circuits and then only for determining "ON-OFF" status situations, e.g., where expected current draw exceeds the meter's capacity. But, aside from "ON-OFF", not much else can be determined, and normally there ARE some circuits that are always "hot", e.g., current to keep the radio pre-sets and computer memories alive. Therefore, measuring current (amperage) will accomplish not only "ON-OFF", but HOW MUCH?

It's the HOW MUCH that is more important, because some (C4 Corvette) circuits are normally always "hot", so it is the amount of current that determines normal or abnormal conditions.

hcbph

Till I found it, I was showing 19 amps from the engine block to the negative battery post with the cable unhooked. I've since found the issue but just suggesting check things like that to see if it could be a potential cause of the battery drain.

hcbph

That was using an ammeter between the alternator bracket and the negative post with the cable unhooked.