Technical Need some electrical hints.

I bought a '35 Ford rod from the family of a guy who almost finished it before he died. It was running and driving but had issues. I have it pretty much straightened out except wiring. He used a Painless harness. It has a pretty good drain on the battery from somewhere. If I don't disconnect it it goes dead in about 8 hours. I've noticed that the cooling fan is on a separate switch and if I don't turn it off before I turn off the ignition, the engine keeps running until I kill the fan. I'm just starting to hunt down the problem. Anybody have any suggestions on what to look for?

 

One method in tracking down a parasitic drain is to remove the ground terminal form the battery and place a test light between the terminal and the cable. If it lights up, you have something going to ground and draining the battery.

Next step is to go to the fuse panel and remove one fuse at a time, if the light stays on, replace that fuse and pull the next one. When the light goes out you have found which circuit is at fault. Now you get to check the accessories on that circuit until you find the culprit.

If the drain is still there after checking every fuse, disconnect the items not ran through the fuse panel, again one at a time, so you can isolate the drain. Items like the alternator, starter, that fan, etc.

There are other methods, but this is my go-to.

That fan needs to be isolated, it is acting as a generator while spinning to keep the engine running. Good fan controllers eliminate this issue. It sounds like you don't have a controller or thermostat if you are running it off a manual switch. You could wire a resistor in line to prevent the backflow of current but I would encourage you to add a control unit and t-stat. They need to be on a relay as they suck a lot of juice.
At Speedway

 

Sounds like the fan has its own feed/power wire that is also running through the ignition switch. I would see how the fan is wired. Should be run through a relay. Disconnect all the fan stuff and see if your draw goes away. Disconnect things one at a time to find the draw. Disconnect either battery cable and put a test light between the cable and the battery post. If the test light is lit, you have a draw. Pull fuses out one at a time until the test light goes out.

 

We must’ve been reading each other’s mind at the same time! Lol

 

If you have a digital voltmeter, the best way I have found to check for a current draw is to check the voltage drop across each fuse in the electrical panel. What you do is put the voltmeter leads on each side of the fuse on the small metal part that sticks out the top of the fuse. Circuits with no current flowing will read zero. When you find one that gives you a reading, that's the one with the current draw. Note that if you have a modern radio in the vehicle, there will current flowing in that circuit. However, the draw on a radio (that is turned off) will not drain a battery in 8 hours. Also, if you have interior lights that are operated by the door, you need to either close the door or disconnect the door switch.

What I like about this method is that you don't have to disconnect anything (except a dome light switch) to perform the test and it is extremely accurate.

 

If you don't already have a DC ammeter, invest in one. They are not that expensive on Amazon (forgive me, Lord). Put the clamp on either battery cables. Note the amperes. Remove each fuse one at a time and note the change in reading. Once you find the circuit (reading of zero), narrow it down to the device by disconnecting each item (Did you get the Painless wiring number/circuit diagram?) Every kit has a book with the circuits and instructions well documented.

Also, you could have a problem with the alternator diodes failure or other "non fused" circuits.

Sounds like the ignition is wired to that fan switch. The control module "control" circuit should be wired to the accessory power from the ignition switch, while the "POWER" to operate the fan should be FUSED from the fuse block with something like a 20 or 30 amp fuse and a larger (12 ga.?) wire. You should have a fan control module with internal relays to make that circuit. The fans should operate based on the engine/radiator temperature. I have a two stage from Summit - A Davies-Craig controller. The good thing about them is that the relays are replaceable. Some controllers have them soldered to the base.

https://www.summitracing.com/search...jtpK7jhRSc0iH94TAaorfRVDAPEKHZJ0aAloyEALw_wcB

The link below may be of help from the Painless website, but first off, find out how many circuits are in your system if you have no documentation and start from there. You may be able to call Painless and see if they can find out based on the name of the guy that bought it in the first place which kit he bought, then get the installation instructions. They do a good job of labeling every wire about every 6 inches with the circuit number.
https://painlessperformance.com/installation-manuals/

Good luck and keep us informed !

 

Great tips guys. Thanks! I'd already tried the test light. I used an 1157 and it pulls enough to light up both filaments bright. I'll continue today. I'd stopped to work on the brakes, which was an interesting story in itself.

 

Isn’t the alternator exciter wire feeding the fan. Diode in-line the fix?

 

Diode is correct, I erred when I used resistor in my comment. Neither is required when installing a proper fan controller though.

 

Well, I pulled all the fuses. No luck. I removed the hot feed to the fuse block from the starter (that also removed the one wire alternator from the circuit). I have continuity to ground. I pulled every relay I could find. The fan feed came off a hot tap on the fuse block and I disconnected it to. Still no luck. It's not a bad short, no smoke and just a tiny spark when I disconnected the battery. I'm baffled but not giving up. To be continued.

 

enough to light an 1157 is decent short..

 

You still have a draw after the fuse box an alt are removed from the mix. I don’t understand where you’re getting the power.

 

Watson, The games a foot. So, at the moment all the fuses are out, relays are out, the fan is disconnected as is the one wire alt. The starter, GM or Ford style (internal or external solenoid?). Disconnect it. Anything else going around the fuse block? Horn, stereo, door poppers, dome light, cigarette lighter/power port, alarm system, pertronix/distributor power, etc? I wired my ceramic heater around the fuse block on one my cars. Not everything runs through that power center.

Since you didn't wire this car, leave all the fuses/relays out and everything disconnected as you described above. Put the terminal back on the battery and see what still functions. There can't be many. Anything still operational is suspect.

 

Need to find if there’s more power wires to the fuse box or other things powered without using the fuse box. Unplug things one at a time so you will know when you hit the problem.

 

After I disconnected from the starter, I was checking for continuity between the hot wire in the fuse panel and ground with an ohmeter. It should have been open. It was not.

 

No stereo, door poppers, dome light, cigarette lighter/power port or alarm system, looks to be an HEI Distributor and I tried unplugging that. It's all Ford drive train but the solenoid is mounted on the starter like a GM, which I'd disconnected. The horn isn't working and I'm going to look into that more. Oddly, there are two flashers on the fuse panel and one had a piece of tape on it marked horn. I have no idea what that's about. The car has a vintage air unit installed which adds to the clutter of wires but the motor speed switch isn't wired up yet. The harness is a Painless 20 circuit. I'm about ready to tear out the Vintage Air just to have some room.

 

Keep looking. Seat heaters, clock, FI...something is running when the key is off. Fun test of patience. @Crazy Steve , ideas buddy?

 

For GM I think 400ma is max draw spec. Thats with draw on some of the modules that never goes away on a new car. Lighting up 2 filaments is quite a bit.

Id suspect the alternator as they will do that if the diodes are bad.

 

A diode will fix the fan feeding back, but so will a relay usually. Too many guys run their cooling fans directly off a fuse instead of running a relay.

 

I suspected a bad alternator, but nothing changed when I disconnected it.

 

Have you tried disconnecting the alternator? A shorted diode in the alternator will draw current all the time. Since you short is constant, it should be relatively easy to find. I had a Lincoln where the solid state voltage regulator would energize the field with the car not running, but not all the time. It was a bear to find because you had to test when it decided to turn the field circuit on.

 

I had a bad one on one of my Camaros but it was intermittent. Like Russian roulette, if the alt stopped at just the right spot (far too commonly unfortunately) the battery would be dead by morning. Other times it would be fine for months. I install kill switches and battery isolators on everything now because I hate shining up a car, hopping in for a drive and it's dead.

You said you disconnected the solenoid on the starter, the main cable is hot always on GM starters. Pull it.

 

So far all advice has been good although I'll throw a few more items into the mix.

There's nothing much worse than troubleshooting someone else's wiring job, particularly unknown draws like this. When pulling fuses, that may not give up the problem. So if you get to that point, the first bit is BE METHODICAL when testing. Do one circuit at a time, fully trace it out, is there any 'extra' wires or one that doesn't make sense? Try disconnecting the connected device; could it be defective or a possible ground path for another circuit? Personally, I'd trace everything to know for sure what's there. Jumping around will just lead to confusion.

Second (and at the risk of sounding like a broken record), none of the aftermarket harness kits I've seen can actually support connecting all circuits to the fuse panels if you have more than bare bones electrical. Sure, they sell you a 20 circuit panel, giving you the illusion you can have a unified panel, but it's fed with only two #10 wires. If you want some chance of keeping excessive voltage drop at bay, that limits the panel to a max of 60 amps (30 amps per side) or the #10 wire length needs to be single digit inches, not feet. It really should be derated down by 20%, that's 48 amps. A mere 2.4 amps per circuit. They then sell you 'relay kits' for things like headlights, fuel pumps, electric fans, and AC to address this shortcoming, but now you have circuits that don't originate at the fuse panel (if wired correctly) so you'll need to identify and trace those. I know for a fact that Vintage Air recommends their systems be fed this way to insure full voltage. The control circuits for these may be fed from the fuse panel however. Lots of opportunities for misconnections if the original installer didn't understand this.

Good luck!

 

I'd try to uninstall the alternator, not just remove the output wire.
Then see if there is still a ground fault.

 

Just for the heck of it, does the car have a light in the glove box?

 

Nope

 

Years ago I had a heavy draw of current on my 55 Lincoln Capri. I thought the battery had just been discharged over time, so I got out the battery booster and connected it up. Immediately the interior lights came on, so I let the battery charge. While I connected the charger to the battery I heard a clicking from the front fender. It turned out to be the horn relay. I disconnected the wire to the horn ring and the clicking stopped. Seems that an insect or small animal had found a way to ground that wire, thereby activating the relay. Why didn't I hear the horns, because they were already disconnected. In short, check the horn relay, and any other relays for a similar situation

 

A faulty voltage regulator can cause this issue. Usually when a set of contacts stick together and won't release as they should. Good luck!

 

I think he mentioned earlier it had a one wire alt, thus no reg.