Are you running a three wire alternator? Neg cable of battery sparking to post signals parasitic draw.

 

It's a one wire.
Is there a way to trace a draw without hooking the battery back up and risking melting wires?

 

Yep. Simply bust out the test light and with the neg bat term undone from the post, hook the clip to neg terminal and touch the probe of test light to neg bat post. If the test light lights up, you've got a draw. If you find you've got a draw then I'd start by disconnecting your alt wire from the battery. if light goes out, you've found your problem. If light stays on, continue testing by removing any other wires hooked at the battery. If its not in your wires, then rehook them to the battery and start pulling out fuses one by one. Once you see the light go out, you've found the area giving you trouble. Hope this helps.

 

Wiring

Best guess is that you have pinched an always hot wire. Check the entire length of the alternator wire to see where it is grounded.

 

Best guess is that you have pinched an always hot wire. Check the entire length of the alternator wire to see where it is grounded.

Yep, very possible,

 

It's gotten dark here and I had to stop working on it but am wondering two things:
1. Isn't the alternator cable usually hooked directly to the battery? The cable that was hooked to mine is wrapped with a handful of other cables and seems to go all the way back to the firewall... don't really want to unwrap and tape everything again but doubt I have a choice.
2. If it wasn't giving me trouble before I disconnected it from the alternator and is now and I haven't done anything else why would it pop up all of a sudden? (Doubt anyone could answer this but just something I'm wondering)

 

Test light stayed lit after you removed alt wire, so you know its not your alt wire. You said you removed another wire and the light went out, so congrats, you've got a start on tracking this wire/prob down, what it does/what connected to.

Answer to 1: Yes, alt cable is connected to a 12Volt source. Typical places its wired to is ofcoarse the battery or a junction block for instance.

Answer to 2: You never know about these cars sometimes. In your case you said everything was working fine until you did the waterpump install. I'd check to make sure you do not have an 'always hot wire' grounded to something. Again, you're test light has now put you on the right track to do some further investigating so further trace that joker down

 

On my 350 ('75 vintage) the 10 gauge charge wire goes from the screw terminal on the alternator along the valve cover to the back of the engine, and then down through a protective metal tube to where it connects to the large lug on the starter through a fusible link.

There is a similar 10 gauge wire and fusible link that runs from the starter lug up through the protective metal tube and over to a junction block on the firewall. That junction block powers the fuse panel.

If you cannot find the short in the charge wire you can disconnect and remove the charge wire that runs down to the starter lug and replace it with a wire that runs directly from the battery to the alternator. For a 100 amp alternator it would be best to use an 8 gauge wire with a fuse or fusible link.

Bruce

 

It's not imperative that it be running right away so I'm going to see if I can trace this wire down to it's beginnings. But if I can't figure it out soon I may just run a cable from the alt to battery with a fuseable link as was suggested.
So there was a wire from a junction box, near the passenger headlight, that ran to the battery + and the other wire on the junction ran across the radiator support area to drivers side. I couldn't tell where it terminated though it seems to also be near where the "alt charging" cable comes from. Is there a voltage regulator on the firewall or near the drivers headlight area that may be where it's coming from?

 

Your original alternator had an external regulator and the diagram on this site shows how it was wired. Its hard to tell how much is still wired this way and what was removed when someone installed a one-wire alternator. Catalog

Bruce

 

Exactly. You should be able to spot a voltage regulator. If not and in doubt, provide a pic of your alternator that shows the exciter terminals.

 

i just went thru alternator troubles on my 58 truk and have learned a lot lately

old gm wiring from the alternator typically used a soldered splice somewheres on the firewall or core support
the splice was in the main hot wire that feeds everything: batt, alt and the fuse panel
after 50 yrs the integrity of this splice can be marginal and might have handled the old 35 amp alt ok
throwing a 1-wire 100 amp alternator is a dicey proposal to the existing wire harness

you should have run a new 10 or 8 ga wire from the hot post on the alt straight to the battery or starter cable and still should
the problem you have created is when you melted the main splice it is wrapped up with 10 wires that may now be fused together
i'd pull all the wrap off the wires to see what damage there is

originally your elco had an externally regulated d10 alternator rated at 35 to 65 amps
if you haven't yet remove the regulator (probably on the core support)

the ''splice''

this is the original regulator hook up, you should only have the main red wire now

 

Ok so I traced the wire back and it was one that hooked to the horn relay. Turns out the pulsing was coming from the aftermarket stereo. Disconnected it since I don't use it anyway, no more pulsing.

However this didn't solve my problem. Reconnected the alt wire after this and test light was super bright!! I'm thinking the issue is with the alternator. Does this sound like the correct diagnosis? I'd hate to get a new one on and have the same problem.

 

Here's an example: Say you've got five wires hooked at the positive post of a battery. You take your Neg terminal off, hook clip of test light to Neg terminal and touch probe of light to Neg post. If the light comes on, you got draw. So next you look at the pos post of battery and its five wires. You undo the pos terminal and take the first wire off, then connect and tighten pos term back to pos post of battery. Do the test light thing again and lets say the light 'lights up.' Then you've just established the first wire you took off (likely without restesting down the road) was not your problem. So you loosen pos term and remove from post again, lets say the second wire you take off is your alternator wire. you tighten pos term back down to post and do the test light thing again. Let's say this time the light does not 'light up.' You've found your problem and it lays with the alternator (could be diodes, etc.), could be the wire so you know now what to look at. So if the light went out when you removed the one alternator wire then I'd remove that wire and hook a lead wire from the alternator to the battery then repeat the test with test light. If light still stays off, it was your wire. If light stays on then you need to test your alternator (do it yourself which is easy except fooling with the two springs when you put back together) or take to an auto parts store and have them test your alternator. Hope this helps,

 

Thanks for that rdobbs, grabed some lead wire and attached it to the junction end (that was hooked to the alt but not for this test) to the battery and no light.
Lead wire to positive from alternator and light is on.
So that says alt. I'm gonna try and run it to a parts store on my next day off just to double check. But that seems like the case.