1994 Mazda B4000, parasitic drain from audio amp, can I switch it

Maintenance/Repairs
21

Cougar, Busted Knuckles –

You ask if I disconnected the wire harness to the amp, put the fuse back in and still had a 300mA load.

Yes, I did disconnect the wire harness, and no, I didn’t see the 300ma load. Apologies for not mentioning that, it is important. That means there’s something in the amp that’s not switching off when it should. I need to review Blackbird’s advice again.

PvtPublic –

You said “Just because there is a blue/white wire from the radio, does NOT mean it goes to a same colored wire in the trucks harness.” Can’t argue with that, except that every wire in the two Metra harnesses matched colors with the truck wiring. So if I’m looking for a truck wire that controls power to the amp, the odds are it’s blue/white. Especially when it’s now one of the only wires still unconnected.

And of course I read the manual the first time. Heck, the radio and amp work, don’t they?

Here’s the key point of the troubleshooting, I think:

With the large black connector pulled from the amp, the voltage at the yellow wire read 12VDC. I pulled the #16 fuse, and the voltage dropped to zero.

And when that fuse is pulled, the parasitic drain drops to (essentially) zero.

So that yellow wire, to my simple mind, is the key to fixing this. Kill the 12VDC from going to the amp, and there’s no more parasitic drain. I might have misread the wiring diagram in the radio’s owner’s guide, but there’s no doubt that yellow wire going to the amp is the cause and solution to the problem.

I appreciate all the interest and advice. If nothing else, I’ve learned that this forum is great. But the dash, not sure yet where, is starting to look better and better for a toggle switch.

22

Well it seems that the standby circuit inside the amp has a problem. I think you made the right connection to it. You could verify that power is getting to the Bl/wht lead and it is switching when you turn on the radio. You might check Ebay out for a replacement. They may have a replacement for a very reasonable price since it is pretty old.

23

Dont use a toggle switch…just like I mentioned before… Install a relay. You can do this fairly easily if you know how to wire Relays. I would just cut the main power feed to the Amp…because the Relay inside the Amp is probably stuck in the ON position. SO wire up a relay that will apply main power to the Amp when ignition power is on. Its pretty ez to do.

You are lucky your Amp is still working for you to be able to do this bec the other failure mode is when the Amp will not power up at all.

Blackbird

24

Blackbird –

You say “Install a relay. You can do this fairly easily if you know how to wire Relays.”

Yes, I can see the advantages of a relay but have never wired one in. Doesn’t seem to be that hard when I picture the schematic for a relay, but I can’t yet visualize it in my truck.

Let me think out loud:

  1. I locate a wire near the amp that’s got 12VDC and is switched by the ignition key.
  2. I cut that wire and put the relay’s coil in line with it. (But worry that drawing some current through the relay will affect the load this wire was feeding.)
  3. I tap into the “large yellow” wire that’s got constant current going to the amp, the one that’s causing the current drain, and connect the two loose ends to the contacts on the relay.

Terminology not exact but I think/hope it’s clear.

I’ve never done this kind of modification. Would a relay like this work? http://comingsoon.radioshack.com/12vdc-40a-spst-automotive-relay/2750001.html

25

Just grab a 5 pole relay…they always have a schematic written on the relay body. For instance Poles 85 and 86 will be the electromag coil inside the relay. Poles 30 and 87 are the connection that gets cut and reconnected by the electromag… Pole 87a is the resting polarity when the coil is not energized. This is all from memory I warn you…but Im fairly certain Ive still got the poles correct.

In this instance…when trying to simply make and break a 12VDC connection… Cut the hot wire…now you have two ends… One end goes to 87 the other to 30… Ground either 85 or 86 and depending upon which one you grounded…the other gets ignition switched voltage… Easy Peasy Japanesey…

YES…your relay would work just fine… I have an enormous bag of relays from all my trips to the salvage yard… Predominantly mine are the 5 pole version of yours…the 5th pole being the 87A pole. But absolutely…your 4 pole is all you need.

Blackbird

26

That was good information, Blackbird, thanks.

I’m definitely going to put in a relay and not a switch. You’re right, that was a bad idea.

But I’ve been thinking about the voltage drop across the relay’s coil. The coil will be in series with the original switched wire. If the voltage drop across the coil is too high, won’t the load at the end of the wire that I’m cutting into be affected?

Thinking back to my electronics training (40 years ago; can it really be?!?), a coil wouldn’t have much resistance so the voltage drop (E=IR) wouldn’t be much either so it should work OK.

Or am I overthinking this?

27

I used a similar 12 V relay from RS for modifying the starter control circuit on my Corolla. Works day in and day out, been perfectly reliable. It has a 30 ohm coil. I think it differs from the one you posted in that it has a pair of 40 amp switches, one is NO (normally open), the other NC. Cost around $5 a few years ago. You definitely want to use a relay designed for cars, b/c then you’ll have the correct type of spade terminals used in car wiring, makes the crimp-wiring easier. Be sure any new circuits are properly fused.

OP … I though you had already determined the phantom current was too high at 300 mA prior to the install of the new radio. So the new radio shouldn’t have anything to do with the problem , right?

28

@Steve_K, what you are proposing to do with the connection of the relay coil is put it in series with the power lead. That is NOT the way you do it, you want the power going to the coil to be in parallel with the existing load. Tap into the power wire and connect that to one side of the relay coil, pin 85 or 86. Then ground the other side of the coil. Connect another wire from the power lead and tie that to one of the switched contacts of the relay, pin 30. Then tie the wire going to the amp to pin 87, the other side of the switched contacts.

29

I’ve just ordered this relay: http://www.amazon.com/Absolute-RLS125-12-VCD-Automotive-Relay/dp/B0002KR9GG/ref=cm_rdp_product?

I’ve no doubt how and where to connect to pins 30 and 87: in series in the large yellow wire that causes current drain when the truck is parked.

It’s 85 and 86, the coil connections, that I’m not sure about. Wiring these terminals in parallel, as Cougar recommends, makes sense and confirms my earlier questions.

My challenge is where to find an ignition-switched wire. I’m hoping to find one at the many wires going into the amp.

Back in a few days when the relay has arrived and I wire it in.

(GeorgeSanJose – “So the new radio shouldn’t have anything to do with the problem, right?” Right, the radio isn’t the problem.)

(Blackbird – “Ground either 85 or 86 and depending upon which one you grounded…the other gets ignition switched voltage.” Hmm, I wasn’t going to do it like that. I was going to go in parallel with an ignition switch voltage wire. But your method does seem easier.)

(I’ve got to stop coming here after dinner and wine. Too.Hard.To.Think.)

30

You’re earlier statement about cutting the power wire and connecting the coil of the relay to the cut leads is INCORRECT. That is putting the coil in series with the power lead. By tapping into a power wire and connecting one side of the coil to the power and then connecting the other coil lead to a good ground point is putting the coil in parallel with the power connection.

One easy way to do what you want to do is get a fuse tap and spare 5 amp fuse. Place the tap on one of the dash fuses and install the 5 amp fuse to the slot to add the extra new load…

31

Cougar, you’re right about me being wrong in how I was going to wire the relay’s coil in series. It was bothering me, too. I’ll definitely be doing it in parallel.

I’d never known of a fuse tap until now. Going to study up on it. Thanks.

I’d been thinking of simply:
– cutting the already-fused, ignition-switched wire,
– trimming insulation from both ends,
– sticking both trimmed ends into a wire nut,
– adding another wire in the wire nut,
– terminating that other wire to 85, one of the coil connections,
– with the other terminal, 86, connected to ground.

You have to understand that while this isn’t rocket science, it’s unplowed fields for me.

32

http://www.escortradarforum.com/forums/showthread.php?t=8274 has good info on fuse taps. I’m on it now.

33

You shouldn’t use wire nuts for automobile wiring, though they will work. Use wire crimp terminals or butt splices instead.

34

All this writing and postulating I could have installed 5 Remote Start systems with a window roll up module and all the relays associated with such nonsense 3X over already.

Just cut that power wire… one side to 87 one to 30… Ground either 85 or 86 and the one you didnt ground goes to Switched ignition power. You probably have a functional switched ignition power wire already AT the Amp… My guess is your relay inside the Amp got stuck in the on position…which can happen… Pull out that multi meter and probe the wires at the Amp…one HAS to be switched ignition power. Hopefully your switched ignition power wire is still working…this can be the other cause of your issue…when the switched power wire remains energized due to another failed relay in the radio… Happens all the time

Now put the wine down, wire the damn thing and be done with it… LOL

Blackbird

35

I’ve just ordered http://www.amazon.com/Add-A-Circuit-function-Littelfuse-FHA200BP-fuses/dp/B009K6ZH6W/ref=pd_cart_vw_2_1_p?ie=UTF8&refRID=135MKZXF0SYY7NQ1WV4F

Tried to find a 20A fuse tap at Pep Boys and AutoZone, but the only ones they had were 10A.

Cougar and Blackbird, thanks again for your advice and guidance.

36

Just use a normal 2 blade fuse… Cut your wire and put female crimp connectors on… One Female for each blade of the fuse. We used to do this all the time to instantly protect a circuit without any kind of fuse holder.

Why are you looking for a fuse tap anyway…that amp wire is already protected with a fuse. Just curious.

Blackbird

37

Finito. Terminado. Fertig.

I think I did a careful job, and am pleased with it. (I’d include photos but you’ve probably tired of this a long time ago.) One neat thing was that the relay fit under the power amplifier and inside the body panel covering the amplifier.

The only thing I’m not happy with is that after I put in the fuse tap, the cover of the fuse box wouldn’t close. So I’ve left the cover off, will put it in a sandwich bag and leave it in the glove box. (I’ll also leave a yellow fuse puller in the bag, just in case.) The fuse box is under the dash, to the left of the steering wheel. I put two long zip ties around it to keep the short wire from the fuse tap from dangling.

“Why are you looking for a fuse tap anyway…that amp wire is already protected with a fuse. Just curious.” Yes, but that amp wire is what was draining the battery. I’m sure, because when I pulled the fuse for that wire, the battery stayed charged.

So I tapped off fuse #15, which powered the radio, as the radio didn’t cause a current drain when the ignition key was out of the truck. Using the fuse tap made it seem pretty certain 1) I wasn’t messing with the radio power AND 2) I was providing power to the amp only when it needed to be there (through the relay coil).

A parasitic drain check confirms everything works, but the proof will be after a few weeks of driving around. And a few days of not driving at all, and seeing if the battery stays good.

Thanks again for all advice, especially to use a relay. That was off my radar, but now see what a useful device it is.

38

“Why are you looking for a fuse tap anyway…that amp wire is already protected with a fuse. Just curious.” Yes, but that amp wire is what was draining the battery. I’m sure, because when I pulled the fuse for that wire, the battery stayed charged.

Of course it did…because it was still attached to the AMP… If you cut that wire PRE Amp…you would have seen the same result. LOL

You really dont need to source power from a Fuse Tap… Find any Fused Constant or Switched power source…Use an inline fuse…and youre good.

Anyways…after much overthinking on this one…I will have to say Good Job. You put in the research and asked all the right questions. For me this is Old Hat…but I do recall my first tries at this so I know where you are coming from. I want to congratulate you on a great effort and a Job well done. I will give you more points when you DITCH the fuse tap and source power in a professional manner. But this will work. Nice work Steve

Blackbird