Electrical Problems

[Black Sun 5.0]

Strange issue: my voltage gauge on my '91 mostly reads low, about 2/3 to 3/4 of the way down. Occasionaly it will pop up to about above the 1/2 way point on the gauge. I have both a brand new battery and a new 130 amp alt., I replaced the old ones for the same issue but I still have it. My mechanic mentioned the easiest way to find which circuit the drain is on is to use a 12 volt test light, disconnect the negative terminal wire from the battery, and connect the test light in between them. If the light goes on, there is a power drain somewhere, and to find it you would pull out each fuse in the car until the light goes out, and this allows you to narrow down the problem. I tried this, got a light, and pulled fuses, the light stayed on. Now I'm assuming that the car alarm system and the radio would each pull from the battery and they have to be disconnected to properly do this test, which I did not do. Does this sound right? How do shops usually trach down electrical issues? Does anyone have any opinions and/or insight into this? I've had this problem since I bought the car 2 1/2 years ago and I'm now determined to track it down. Another odd thing associated with this: sometimes when I hit the brakes or turn the headlights on, the lights will flicker and the radio resets. Sorry for the long post.

 

[jrichker]

Your process sounds correct. Most of the time battery's that run down by themselves are the result of something like the glove box or underhood light remaining on all the time. It's the little things that you don't pay attention to that can drain a batery.

As far as low voltage while the car is running, use a digital voltmeter right at the battery to check the actual voltage.

3G altenator installations MUST have the 4 gauge wire & fuse, or there will be problems. 3G installations should also have a 4 gauge ground wire run from the engine block to the same place on the chassis as the battery ground. The stock ground on the back of the engine isn't big enough to do the job, and is often damaged or missing.

The flickering lights and resetting radio sounds like a loss of voltage, which would mean that some of the power wiring near the starter solenoid is bad. The other possiblity is that the chassis ground for the battery is bad. Either one would also account for your low charging voltage problems.

 

[Black Sun 5.0]

What would make you believe that the flickering is being caused by the wiring near the starter solenoid? Since I'm a bit of an ignoramus, I have to ask: where is the starter solenoid? Also, is there any chance that any of the alarm wiring could possibly be routed through here? I'm just trying to narrow down my headache here, and I really want to avoid paying a shop to deal with this. As for the 3G alt, I had a shop do this and the wiring is indeed some heavy gauge, so I'm not worried about the alt itself. I also had this issue before the 3G was installed.

 

[jerry beach]

Re-read jrichker's post. Did they install the engine ground he spoke of? Are your battery cables in good shape. As he stated, hook a volt meter to the battery and see what the alt is putting out (voltage wise) with the engine at idle. The stock guage may just be broken. Is your battery dead in the morning? Do you have to dissconnect the cable when you park it?

Look for simple stuff too, like coins in the cigarette lighter. My bulbs in the vanity mirrors were burning all the time. I took them out. When you are doing your short test, are you making sure the top light is off, and the hood and trunk lights...?

 

[Black Sun 5.0]

This doesn't appear to be an 'overnight' thing, the car always starts. The battery cables are brand new, as are all of the alternator cables. I had my local Mustang shop install everything. The problem is while the car is running. While running, it appears that the gauge is reading low, but sometimes it reads just above the half way point. One thing I noticed was that when it was frigidly cold out here, that's when the gauge read above the half way point. It's warmed up a bit since, and now the gauge has sunk again. I also get check engine lights, which may or may not be related.

 

[jrichker]

What would make you believe that the flickering is being caused by the wiring near the starter solenoid? Since I'm a bit of an ignoramus, I have to ask: where is the starter solenoid? Also, is there any chance that any of the alarm wiring could possibly be routed through here? I'm just trying to narrow down my headache here, and I really want to avoid paying a shop to deal with this. As for the 3G alt, I had a shop do this and the wiring is indeed some heavy gauge, so I'm not worried about the alt itself. I also had this issue before the 3G was installed.

Follow the battery + lead to the first junction point. That will be the starter solenoid. All of the electrical system gets its feed from there. That is where the fuse panel gets its power feed, and the fuse panel feeds other things like the radio. There are a number of fuseable links (pieces of wire that act as fuses) that have their point of orgin near the starter solenoid. These fuse links can be sources of intermittent connections and high resistance connections (connections that don't pass all the electical power they should pass).

My orginal comments about the importance of grounds can play a key part in fixing your problem.

 

[Black Sun 5.0]

Trust me about the grounds, I've had 2 different shops look at them, one a Mustang shop, and no one found any problems. I was very suspicios about the grounds, and I still am to a degree. As for the starter solenoid, your description is where I thought it was, there are a lot of wires there and it does look a tad messy. I'm starting to eyeball the alarm, there's a small box there that arcs sometimes if you mess with it. I think the radio and alarm installs were home jobs, so who knows what kinda mess the previous owner created. I'm going to disconnect the alarm connections near the solenoid this weekend if I have the time, see if I'm right about it. Thanks for the help. If you have anymore ideas, feel free to fill me in.

P.S. On a side note: do you think a poorly grounded O2 sensor can be damaged by this? I had new O2's installed last year, but the shop later found one was not properly grounded. My gas mileage blows, even after they were changed.

 

[Black Sun 5.0]

Ttt

 

[jrichker]

To find high resistance connections, and excessive voltage drops, put one voltmeter lead on the negative battery post and one on the engine block. More that .5 volt drop indicates a dirty connection or bad cable: next try from negative battery post to body ground at the firewall.

Use this process of measuring voltage drops across wiring and connections to find the one that is more than .5 volt drop.

 

[Black Sun 5.0]

Excellent, but one more dumb question: do that with the car running or off?

 

[jrichker]

Excellent, but one more dumb question: do that with the car running or off?

I would do it with the engine running. The reason is that the alternator is putting out voltage (if it is working and you have done the other steps in my previous Post). It will enable you to see the current flow from the alternator to the battery and the from the battery (or ground) to the accesory side of the ignition switch and fuse panel. Do the shake and wiggle with connections and wiring bundles to look for open circuits.

See See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

for help in locating some of the critical points to check.

 

[Black Sun 5.0]

Thanks again! :worship: