Electrical pulsing, need help!

[bgharris28]

Hello again VMF’ers!
Got another weird problem…
I upgraded my gauges to autometer phantoms during a full blown restoration of my 67 coupe. My symptom is a dead battery every few days of not driving it. I have tested the battery and the alternator and both check out. Here is where is gets weird though. If I disconnect the positive lead of the battery and then clip a test light to the terminal and the cable, I get a dim pulsing light. If I open the door or turn the lights on the light glows constant. While the light is pulsing however, I can hear a pulsing sound from around the radio that corresponds to the light at the battery. I got upside down and looked under the dash and it seriously seems like it’s coming from the radio. I unplugged the power clip from the radio and the test light started glowing constant (as if I were drawing electricity from the dome light). Common sense would tell me that the gauges are grounding out somehow but I can’t ignore the sound coming from the radio.
A little background on the wiring: I did not mess with the existing wires to the radio at all, but did upgrade to a new radio (the former was aftermarket as well). The wiring harness for the gauges are still intact but I did jump from the original harness to make the necessary leads for the new gauges. (for better or worse) No volt gauge with the new ones. And I used the existing light bulbs for the backlights.
I did take a VOM reading of the negative terminal and pulled fuses to try to find a culprit but my results are inconclusive d/t having an old needle style VOM that dances around a little on its own. What do you think the likelihood of this being either the voltage regulater (OEM), the gauges, or the radio? Also what can I do to narrow it down before I give up and drop the steering column and remove the gauges, which are a total PITA for me? Thanks to all that provide help!!

[rayhicks1969]

I did this a few months ago, ended up pulling the radio and cutting every lead I did not need. This left just hot, ground, 2 speaker wires and antenna. I had a bare wire tip on the radio harness that was intermittent to ground. Just an idea.

[bgharris28]

Thanks for the advice...got me thinking...

So I have a plastic (cheap looking) bezel I got from cj's and I wonder if the radio itself now needs to be grounded to the chassis? There is a ground wire in the harness going into the radio but I wonder if that might be my problem. The pulsing I described in the original post is very very reminiscent of a tic-toc of the clock....

[TOMs67]

You're on the right track. With your test light hooked up between a battery cable and the battery post, the light will light when there is any current draw on the battery. A further benefit is that the light will limit the amount of current draw based on the size of the bulb in the test light. With everything turned off -- interior lights too, the test light should be off. If it's on, even dim, then there is current draw. You can pull fuses and when the light goes out that is the culprit circuit.

[bgharris28]

Thanks! I was hoping that yesterday but after removing all the fuses the light still pulsed. I'm hopin it's just years of PO's wiring around fuses and not the electrical anomaly never before witnessed my mankind. The fact that the radio is buzzing as the light pulses makes me think that's the culprit but the weird thing is that there is a ground going into the radio. Could it be that the bezel isn't grounding the radio as its plastic instead of original metal & that's causing a ground fault each time the clock calls for power to tic itself along?

[rayhicks1969]

Just thought this, make sure your ground from engine to firewall is good.

[bgharris28]

Ok I have an update.
I tried grounding the radio with no avail. So I started looking at the yellow constant wire going into the radio. When I unplug the harness and put the test light to it the yellow wire shows constant. As does the test light at the battery. (The pos lead is unplugged and jumped with another test light) now when I test the yellow wire while its plugged into the radio it pulses, as does the one on the battery. The yellow wire should be constant and the test light at the battery should be off all together right?

This is becoming a nightmare! All the blood is rushing to my head from being upside down under the dash but I can't seem to figure out what's wrong. It's a brand new radio for Pete's sake.

Ahhhhhhhh. Please help!

[bgharris28]

Anybody?

I have replaced my solinoed and vr and still have the problem. The battery is new (2 months) and my alternator works fine. I can't figure out why I have a pulsing current going to the radio when plugged in with a pulsing sound coming from the unit. When the yellow wire is unplugged it's constant....no pulse. I have tested all the fuses and just can't get the test light to go out while its bridged into the battery. Only blink when the radio is hooked up. Can the memory of a stereo really sap my battery over a few days? Is there anything that I could put inline on the yellow wire to prevent this? There is also some sort of box wired in to either the red or yellow (I think it's some sort of filter though). Can't remember. Could this be part of the problem?

I read that when the test light is connected to the positive terminal of the battery and the unplugged cable there should be no light at all unless there is a significant current drain. I still have a constant light on even when I pull the wire harness out of the back of the radio....I assume that's because the ground wire has also been pulled? Could it be I'm pissing up the wrong tree?

I know this thread isn't getting a lot of hits but if anybody out there can help me solve this riddle I will be one step closer to having my old horse out of the barn & back on the trail.

[rayhicks1969]

Yellow wire?, Red for hot, Black or green , ground. This gives you 12V power to the radio. If you dont need the Yellow, get rid of it. Pulsating voltage sounds like AC and you aint gettin that out of a car battery. In line filters are for ignition noise. Make sure you have GOOD grounds.

[bgharris28]

Right the yellow is my constant power 12 v
Red is my ignition. Only on when key is turned
Then the ground. I have regrounded with a separate wir to see if that could be it but no difference.

Thanks for helping. Are there any check sequences you would recommend.

[Gary's 67]

I think I would try to find out what the "box" is that the red or yellow wire is coming from. If you need the yellow for constant power to the radio to keep the programming, try to temporarily run a new wire thru a fuse from the pos battery to the connection on the radio for the constant power. If this works, find a new constant power source (fused) for the radio or installed a new fused wire from battery and delete or cap off the yellow wire. Electricity can do some weird stuff sometimes, especially if somehow backfed thru another source or in series with something else.If there is voltage on the yellow, it shouldn't be draining the battery if its not hooked up to anything or capped off. I would try this temporary wire and see if it solves anything. just my $.02

[Gary's 67]

I know some radios had or may still have a connection for a power antennae- just guessing here- just doublecheck that the connection to the radio is for constant power for the programming.

[bgharris28]

So I started over and pulled all the fuses while the test light was hooked up, as before and after holding all the fuses in my hand, I decided that was not where my problem was. So I went back under the hood and systematically pulled wires until I found one on the solenoid that made the light go off! I hooked the battery back up and all the fuses, leaving only this "red wire" off. went through and checked all my lights blinkers horns radio, and everything else and all was normal. Next i started it up an low and behold...the tach, oil pressure and temp gauge werent on. So I have found where my ground issue is coming from, I just have to trace it down and figure out how to solve it. Ran out of daylight so I will have to do it tomorrow. Any tips for fixing the ground (or at least narrowing it down)?

Thanks again to all that have read me whine and complain and still offered sound advice!

[bartl]

Sounds like somebody tapped the radio into the IVR (Instrument Voltage Regulator) behind the dash. It supplies a constant reduced voltage for the gauges in the form of a pulse. It gets its feed from the ignition switch "C" terminal, if I'm not mistaken, which is hot when the key is ON only. The "A" terminal, where accessories like the radio, and wipers feed from is hot when the key is ON and in ACCY as well. The "B" terminal is feed from the battery and the "S" terminal goes to the solenoid. Could be an internal short in the radio backfeeding the ignition or crossed wires. Sounds like you're on the right track, though.

[bgharris28]

1 strep fwd 2 steps back.

I figured out the parasitic drain was coming from the wire on the solenoid that feeds the tach, oil & temp gauge, albeit a very small drain. I wanted to see if moving that wire to an ignition source instead of a constant 12V would have any difference...

well it does. the gauges work fine when the ignition is turned on and shut off when the car turns off. Problem solved right? No way. Now for some crazy reason, the light ring on the gauges dont work...the turn signal lights, brake light and hi-beams still function correctly as do the head lights tail lights etc., just not the actual gauge lights (autometer phantom). upon checking the fuse box, I am no longer getting power to the center fuse in the panel. (2.5 i think) the fuse is good (tested) but no current at all coming down into the panel. I jumped it from another source to see if the lights worked and they did so im not in trouble there but I fear I may have fried my headlight switch