Battery distribution to the fuse box

[HISSIN50]

Hello,

Had an interesting experience with the '94 today. While stopped at a light, the minutes on my dash clock went black (still showed the hour just great) and the radio shut off. The HVAC blower motor was running almost nill too (it was on medium). Voltmeter was reading about 12 volts.

If I goosed the pedal ever so slightly, my volts came right back up to high 13's, the blower motor worked normal, clock lit back up and the radio turned itself back on. The idle is normal - I hate to interpolate the stock tach, but it was at about 700 RPM (normal). Appearing to have a bad connection, I redid my alternator-to-distribution block cable (the old one was dropping about 400 mA; the new one drops 5 mA). I had this all wired up already, but not connected (I was waiting for my next battery disco' to make the connections).

But I seem to have a voltage drop to the interior fusebox (voltmeter at the box reads a volt lower than at the battery). Does anyone know the pathway for how juice is carried to the interior fusebox? Is there one large cable that ingresses the interior fusebox and then splits off as needed? Starting and ending points would be great (I will probably either clean the connections or just run a new cable).

I have not had the SN fusebox out yet, so I dont know what to expect. I dont fit under the dash too well so I was hoping to get some info on what I need to do or chase exactly before I start messing around under there.

BTW, I know the simple answer is to up the idle a hair, but the idle was as it has been and I would like to find the source of the issue rather than band aid it. I dont think the alt is on the outs (could be though) since it ramps back up with the slightest throttle bump. This happened at every light the whole way home too - wasnt a one-time anomoly.

Thank you for all info!

 

[OrangeMustangGt]

whell i can definatly confirm that when you have low voltage, that crazy stuff happins...mine does that also. If i were you i would worry about the ALT or the battery first, as you say it ramps up when you idle it up....seems like a mechanical condition

 

[CManT1914]

Yowza JT, I really wish I knew electrical so I could help you out, but I'm lost when it comes to that kind of stuff. I can offer some not so useful advice though. Don't bump the idle up to avoid it. That's a band-aid solution like you said. Like running an FMU with a 10lb blower. TTT for ya.

 

[mytight95]

did you check voltage at the battery with the car running....... if so thats why they are different, IMO


jason

 

[HISSIN50]

did you check voltage at the battery with the car running....... if so thats why they are different, IMO


jason

Jason, explain what you mean further please. Thank you. Yes, I do load testing and voltage tests with the car running and a load on the cables (voltage-drop testing with lesser loads is not very revealing).

Green, it only takes about 100 RPM increase in RPM's to be back over 13 volts. It is kind of like the issues fox guys have with U/D's and 2G alternators. Since a hair of RPM increase brings it back up, I dont think the alt or battery are at fault (which is not to say they are not).

Chris, thanks for the bump.

Thanks again guys.

 

[mo_dingo]

Jason, explain what you mean further please. Thank you. Yes, I do load testing and voltage tests with the car running and a load on the cables (voltage-drop testing with lesser loads is not very revealing).

Green, it only takes about 100 RPM increase in RPM's to be back over 13 volts. It is kind of like the issues fox guys have with U/D's and 2G alternators. Since a hair of RPM increase brings it back up, I dont think the alt or battery are at fault (which is not to say they are not).

Chris, thanks for the bump.

Thanks again guys.

That sounds like you have a bad ground, or your voltage regulator is bad.

Check all of your ground connections, the 3 at the battery, The one on the right side of the timing cover near the middle, and the front of the oil pan. I can't remember any more. Your problems sound exactly like a bad ground.

Once you eliminate a bad ground out of the equation, try this below.

Hook your DVM test leads to both pos and neg at the battery with the car running for at least 5 minutes at idle (should give the regulator time to drop down to 13.6). You should see at least 13.6 at idle. If not, you likely have a charging problem. Now keep the ground lead at the battery, and put the pos lead to the 8 gauge wire that hooks up behind the alternator, at the very top. It will have a red cover that you need to pop loose before you can get access to it. You should read around 13.6 - 14.4V or maybe higher. If the alt read 13.6 or higher, and the battery reads less than 13.6, you have a bad connection to the regulator or the regulator is bad. Probe the input/output of the regulator and see if there is a voltage drop. If there is, it's bad and you need to replace it.

If the alternator reads less than 13.6, you need a new one....sorry.
Scott

 

[mytight95]

he covered pretty much what i was saying above......... you are gonna get 13 or more volts at the battery with the car running, but only 12 at the fuse box etc. because of the voltage regulator, i think you prolly need an alternator rebuild......

Don't know about where you live, but we have an alternator specific shop here...... they will rebuild one for 40, or test the system to see what is wrong pretty cheap as well....(like 15$)




jason

 

[HISSIN50]

he covered pretty much what i was saying above......... you are gonna get 13 or more volts at the battery with the car running, but only 12 at the fuse box etc. because of the voltage regulator,





jason

Huh? Last time I checked, the battery gets regulated voltage too.
Thanks for the reply though - that answer is in the area of info I was lookin for.

 

[BlownFiveLiter]

Maybe bad ignition switch? The clock, radio, and blower motor all go through the switched voltage source in the steering column first, so it could just have some normal wear & tear in it, causing a bad contact. I'd probably start there, and work my way back to the battery or alternator.

 

[HISSIN50]

Maybe bad ignition switch? The clock, radio, and blower motor all go through the switched voltage source in the steering column first, so it could just have some normal wear & tear in it, causing a bad contact. I'd probably start there, and work my way back to the battery or alternator.

That was a thought I had too. I dont know if SN ignition switches are like foxes in that before they go south, a couple circuits start to get funky (for a fox, the turn signals, HVAC blower, and radio, as a matter of fact) will shut down. But those ignition switches were a turd - I would have expected more from an SN switch.

I will check around - are new switches cheap (fox switch is 15 bucks)? I might have to do that for peace of mind. I need a new lock cylinder anyhow - get it all done at once.

Thanks bud.

Scott, I forgot to reply to your post earlier - the alt is fine. If it is a ground issue, it is localized to a few circuits which share uncommon fuses - not my first guess or avenue of pursuit. Great info though!

 

[mo_dingo]

Scott, I forgot to reply to your post earlier - the alt is fine. If it is a ground issue, it is localized to a few circuits which share uncommon fuses - not my first guess or avenue of pursuit. Great info though!

I had thought you said that you probed the battery terminals w/ the car running and you were under 13V, so that is why I went on the path that I did. It shouldn't go less than 13.6V at any time, AFAIK. Maybe I am wrong....who knows.

Good luck man.
Scott

 

[HISSIN50]

I had thought you said that you probed the battery terminals w/ the car running and you were under 13V, so that is why I went on the path that I did. It shouldn't go less than 13.6V at any time, AFAIK. Maybe I am wrong....who knows.

Good luck man.
Scott

Scott, sorry for the confusion. The point of this thread was to find the wiring pathway to the interior to fix the voltage drop. I was reading 12 volts inside the car (aftermarket voltmeter, which I had checked with my DMM to confirm was reading correctly). The readings at the battery and alt (identical after my new cable) are fine. I am getting a 1+ volt drop to the interior.

I dont think you are wrong. I will say that in general with all cars, I dont sweat occasional periods of 12.6 volt readings even (personally) - at hot idle with tons of accessories going it can be normal IMHO. I dont set my idle higher like some of you guys do (if I had it at 850-900 RPM, I would be lookin good at all times). Having had a 65 amper in the fox, I dont sweat stuff too much.

I do appreciate the articulate posts though - nice that you got my back.

 

[tmoss]

There is not just one source of power to the fuse box. Some come through the ignition switch and some come direct from the relay cluster of fuse links.

 

[HISSIN50]

There is not just one source of power to the fuse box. Some come through the ignition switch and some come direct from the relay cluster of fuse links.

Thanks Tom.

I am gonna meter each fuse in the box and isolate which circuits are dropping and then trace backwards. I need to check schematics, but figure I will be heading toward the ignition switch (these are all key-on items). When I referenced one cable before, I meant to ask if one constant power cable came from the battery to the ignition switch (or some other distribution means), where key-on power spydered out.

We all know I am not articulate - I have not slept in 30 hours. Bear with me.

 

[tmoss]

Color coding may not be right for you, but this diagram illustrates what I'm saying pretty well.............

 

[HISSIN50]

Thank you Tom - A diagram I know well!