Both headlights burned out tonight... Why?

[Green Monster]

Okay. Got it. So I disconnected both halves of the plug from the firewall, as in, it they are removed from the firewall. Checked negative side of my battery with my volt meter. I placed the meter inline of the ground cable and negative terminal. 9.95V is my reading on a battery reading 12.5V. What does this mean?

I did check my alternator while the engine was at idle before disconnecting the firewall wire harness. It was putting out 13.6 volts. I'm not sure if that helps.

[jaros44sr]

Your going to have to back to 72lb4X4's post and try to understand that, I don't follow it but it is lenghty, maybe you'll have better luck, try to follow his directions because I have never had a spark on the neg. side of the post. Must be something with one of your grounds???? J.

[Yukon Jack]

So glad to see you're making progress - I'm very electrically challenged so I'm trying to use this post to educate myself some. I will be book marking it for future reference.

[red71cheyenne]

Ya, with the bulkhead connector disconnected, that doesn't mean you've killed all the power. I know I have power running around it in several places and stereo's are notorious for having separate power leads running to them. If it is under the carpet and shorting to the frame, that could be one of your drains. About your only hope now, is to start taking a look at all the wires that are running under the hood and see where they all go from the junctions. Your dead battery probably is the end culprit, but you may have other issues that caused it to go dead, ie. the drain from something shorting to ground. Good luck and let us know if you need more help! Jeff.

[old man jimmy]

Could it be you had this drain problem before your headlights went south? How often do you use the truck? The woofer wires you discribe, I see no reason for them to have started being a problem because your lights went out. Could be melted insulation on a couple wires inside your wire harness. But before I spent too much time on searching your harness. I would deciede if you want to keep your dual battery setup. (myself I would. Nice back up) If you do I'd replace the dead aux. battery, hook it up and go from their. Been 30 some years since I've worked on aux. battery hook-ups, so memory not wat it once was. But I would fix all known problems before I started looking for new ones. The ford selenoid thingy I was talking about. Your hot (+) wires from batteries would go to it. If you don't want to keep dual batteries, then we'll talk you through wireing it for one.

[Green Monster]

I removed the dead battery. Then I disconnected the + cable from the charged battery and placed my volt meter inline of the ground cable and the - post. The meter still showed 10.5V. I thought that was strange. I moved the battery to my Mustang and placed the grounded the black wire on the meter to the strut mount and placed the red wire of the meter to the - post. I did not touch the + post. Same result: 10.5V. Looked to me like the battery had shorted, or something. Seemed strange to me.

I went back to the Blazer with no batteries in it. I traced the wires from both batteries. I will create a diagram using the Microsoft Visio program I have at work then post it. There is too much going on to try to describe. The diagram would work a lot better. I found one wire coming off a junction block that had the insulation worn off in two locations. It was apparently wedged between the driver side battery and the radiator support. It had grounded it self to the support. I tapped that one to protect it for the time being.

So decided to pony up some bucks an purchase a new battery since my old battery appeared to have signs of a short since it read voltage to the ground regardless if the + post was connected or not. I brought home a new battery and plopped it in. Connected the + cable and then connected the meter to the ground cable and the - post. I got a reading of 12.5V.

I disconnected the cable from the + post then checked the meter again. 0.0V. That was a good sign since my old battery showed a 10.5V when grounded no mater what.

So I then connected the + cable, disconnected the bulkhead harness, and then connected the meter to the ground cable and the - post. I got a reading of 0.0V. That tells me I either have a short inside the cabin or the radio is drawing power for memory. I will investigate further tomorrow by disconnecting my radio.

Things are looking up though. I think I understand what happened now. The battery on the driver side died. The voltage regulator was allowing a charge to both batteries since they are connected in a series. The driver side battery would not take a charge so the charge was being accepted on the passenger side battery which became overcharged and shorted. This is when my headlights blew too. The voltage regulator may have failed too. I replaced the voltage regulator.

I plan to eliminate extra battery along with the damaged wiring to the extra battery. I do have some questions about a hot connection on the radiator support wall. Both pink wires from the batteries run into the connector (picture 1) then one wire goes to the fuse block. That pink wire comes back out of the fuse block (center most of picture 2) to the tach. A brown wire comes out of the tach and leads to the fuel tank.

I would like to just eliminate this connector at the radiator support and run one battery wire straight to the fuse block. This would eliminate two junctions, one connector in picture 1, and one battery. What do you think? I can create a diagram of what it looks like by tomorrow afternoon, then make another of what I want to do. Could you walk me through the process, old man jimmy? Should I just follow the wiring diagram linked a the beginning of this post?

Picture 1



Picture 2

[Green Monster]

Originally Posted by Green Monster

So decided to pony up some bucks an purchase a new battery since my old battery appeared to have signs of a short since it read voltage to the ground regardless if the + post was connected or not. I brought home a new battery and plopped it in. Connected the + cable and then connected the meter to the ground cable and the - post. I got a reading of 12.5V.

I disconnected the cable from the + post then checked the meter again. 0.0V. That was a good sign since my old battery showed a 10.5V when grounded no mater what.

So I then connected the + cable, disconnected the bulkhead harness, and then connected the meter to the ground cable and the - post. I got a reading of 0.0V. That tells me I either have a short inside the cabin or the radio is drawing power for memory. I will investigate further tomorrow by disconnecting my radio.

I have a reading of 12.5V through the ground when the bulkhead is connected.
I have a reading of 0.0V if the positive post is disconnected.
I have a reading of 0.0V if the bulkhead is disconneted while the positive post is conneted.

I'm not sure about the factory option or add on. I will check this afternoon. If it was factory, I would like to keep it, but have it wired up right.

[old man jimmy]

Ok guy, You are talking 12.5 volts from ground to ground, right? If your reading goes to 0 when you unplug your firewall connector, should be simple to track. If I'm reading this right, your drain has to be behind your fuse block. Time to start pulling fuses, ONE AT A TIME. And check your voltage at ground each fuse. Then put that fuse back in, and go on to the next. When you find the fuse that gives you a 0 reading at ground, see what it says it's for. Should tell you where to look. Check any unfused wires plugged in at fuse block also. Just make sure to plug them back in where they were. By the way, Just noticed something. When you were testing this & that with the hot (+) cable off, all that was telling you was that the battery had a shorted cell, and when you hooked the ground up to metal you supplied a path for the current to flow to. You would have got your 10.5 volts or what ever it was, if you had hooked the cable from the ground on battery to a metal workbench, fence or anything metal. I had never heard of testing for a short that way, but hey. Now we know a new way for testing a shorted battery. I have a regular battery tester, but for you guys that don't, you might want to keep it in mind. Seems to work. See never too old to learn.
Tom

[Green Monster]

That is correct. When I unplug my bulkhead connector my drain drops from 12.5V to 0V. Sounds pretty simple to narrow down from what you told me. I will investigate further to determine where my drain is. Looks like I'm on the right track. Should have this thing figured out by this afternoon since I have the day to work on it.

That shorted cell was messing me up. All my testing was pointless with that bad battery in there. I never had a shorted cell, nor did I know one could exist. Now I can go about tracking the drain down with all the instructions all gave me earlier.

My earlier post about the wire going to the tach then the full tank may be wrong. I have to check that wire again. What's the deal with all the wires coming out of my fuse panel? Was this all "creative wiring" or is it supposed to look like that?

Initially all these wires all over the place were a bit overwhelming. Now that I know where they go to and from it makes it a lot easier to comprehend what's going on here. Most of my problems appear to be from wiring that was done by previous owners. This electricity issue is really not that intimidating anymore when the wires are easy to track down.

Dealing with electrical issues is a task in of itself. Giving advice for electrical issues is pretty difficult. What would possess you guys to give electrical advice to someone who has no clue what he is doing?!!! Thank you for all your help so far, everyone. I have enjoyed this learning experience.

-John

[old man jimmy]

Good luck today. We're all learning all the time. I have a question for you. How did you have your meter hooked up when you were getting your 10.5 volt reading? And are you sure you're not talking amps. not volts? And from what I could tell from your pictures. Your battery set up looks pretty factory. I've got a shot battery setting around in the garage. I'm going to see if I can get some juice in it, and try your battery test. I think you may have stumbled upon something their. May not be a new idea, but it's new to me. See, I learned from you. You fuse panel has had a few wires added, but all of our has. Looks to me that he did a fair job of it though. And your tach wire should go to your - side of your coil. Or connect to that wire someplace.
Tom

[Green Monster]

Here some additional pics of this crazy set up for those interested.
Passenger side. Battery removed.


Damaged wire linking batteries.


Driver side. Battery removed.

[Green Monster]

I don't see anything on this wiring diagram about going from the battery to the fuse block. This appears to more "creative" wiring.

Originally Posted by farside847

Here are some higher rez versions to view online:

[old man jimmy]

Sounds good. But look back at your last post. You stated you had a meter reading of 0 volts on ground with firewall plug plugged in. And 0 volts with firewall plug unplugged. But you think you're still getting a draw from something inside your truck. Unless that's a typeo, You don't have a problem anyplace. So time to quit unplugging wires, like radio. Remember what happened last time. Be glad to talk you through getting rid of your aux. if that's what you want to do. But if it were me, I'd just get another battery for the aux. side. I used to use mine for camping, and always wished I had a dual battery set up. When you're up in northern Nevada, 70 miles from anything, it's nice to have a back-up. I even order mine with 4 speed for that reason. I can always find a hill to roll start it. You can make them fail safe with a switch between batteries so they can't do what yours did again. But like I always say. Make them the way you want them. Forgot to ask. Is that a factory option or add on? Should say on your glove box door.
Tom

[Green Monster]

Originally Posted by old man jimmy

But if it were me, I'd just get another battery for the aux. side. You can make them fail safe with a switch between batteries so they can't do what yours did again. But like I always say. Make them the way you want them. Forgot to ask. Is that a factory option or add on? Should say on your glove box door.
Tom

I checked the inside of the glove box and the auxiliary was a factory option along with the hand throttle cable on the dash. So I have decided to keep the auxiliary battery option. I prefer to keep the Blazer stock, with the exception of the lift wheels and tires. So how does this fail safe switch work? How do I set it up?

[old man jimmy]

Now you're opening up a whole new can of worms. First off you have to make up your mind what you what it to do. Their are many ways to rig them. If you want to control them from inside the cab, or under the hood etc. But remember, the more complicated you set them up, the more likely they are to failure. I'd simply run your hot lead from aux. battery through a heavy duty throw switch. Now days they have a bunch of after market switches that do the same thing and cost a lot more. But most use electrical selenoids (like the ford selenoid was talking about) and require a lot of wireing. Yours already is fused. That's that relay (fuse) in picture one. And It's already set up from factory to charge both batteries. So if it were me, I'd simply put an isolation switch on the aux. And call it a day.
Tom

[Green Monster]

I don't really have any special needs for the auxiliary battery. I just want to keep the Blazer close to original. Would an isolation switch would prevent the battery from being used and being charged if the switch were off?

BTW- I took the Blazer out for a spin last night. It runs like a champ. I learned a lot while saving money fixing this problem myself. Thanks guys. The Blazer is so much more enjoyable when driving it after you repaired it yourself. Thanks again for all of your help. The wiring diagram was a huge help. This is what we were dealing with:

• One dead aux. battery
• Action: Removed
• Action: Will replace
  
• One shorted battery
• Action: Replaced ($100)
  
• One malfunctioning voltage regulator
• Action: Replace ($30)
  
• One shorted 12R wire along radiator support caused by auxiliary battery hitting the radiator support wall. The auxiliary battery tray has rusted away which will not allow battery to be secured
• Action: Repair wire. ($0)
• Action: I will have a new tray welded in ($?)
  
• Two headlights burned out
• Action: Replace ($40)

Not too bad. $170 While I was messing around I cleaned and wrapped some ugly spliced wires that were flopping around to the alternator and headlights. Now the wires are wired directly to the correct harness and soldered to the female connectors.

[old man jimmy]

Yes to both of your questions. But you would want to kick the switch on once in awhile to keep the battery charged. Don't let the dual batteries scare you. It's factory, and probably been doing fine for 35 years the way it was. Your problem came from not replacing the aux. when it died. Even then not often they do what yours did. But I would still put in a switch. But I'm old fashioned, I like mechanical things that I can control. Less problems.

[69TowRig]

The wire joining the two batteries was a huge issue, I found one like that on mine that kept killing my battery when I wouldn't drive it for a while. The insulation had split and whenever the humidity was up the voltage would push to the radiator support. Found it because eventually the copper left a nice patina green on the rad support where the wire touched it. Replaced that wire and haven't had a drain issue since.

[Green Monster]

I have not driven my Blazer since having these issues. The battery drains dead when I park the Blazer for extended periods of time, such as overnight. I keep the ground cable off the battery while the Blazer is parked in the garage.

I replaced the damaged wire running along my radiator support yesterday. The old wire had grounded to the radiator support in three locations. When I connect the ground cable to the battery I get a spark. Obviously something is still drawing a decent amount of current.

After I replaced the wire I took my Blazer for a spin around 11:30 PM last night. It ran great for the first 15 minutes. The belts were a little noisy at idle from sitting but they soon quited down. I turned to enter an expressway. I floored it. The exhaust let out a loud, throaty growl. As I the engine revved to higher RPM the headlights both blew. I slowed the beast down and pulled to the shoulder of the road. I tapped the high/low beam switch and turned my low beams on. Whew. The low beams worked. I realized I must have burned the filaments in the high beams. I drove home on the expressway trying to keep the speed down to ensure I did not blow my low beams. 10 minutes later, on my way home, I mildly accelerate while doing 65 mph. The driver side headlight flickered and POOF! I have one headlight left; the passenger side. I look at the RPMs and the motor is turning 3,500 RPM. I slow the Blazer down and bring Green Monster home. I'm still not sure what's wrong here.

I still have the same problem I had before.
Do you think the headlight switch could be causing this issue? I did not replace it. Shouldn't the voltage regulator stop this from happening?

Updated:

• One dead aux. battery
• Action: Removed
• Action: Will replace
  
• One shorted battery
• Action: Replaced ($100)
  
• One malfunctioning voltage regulator
• Action: Replaced ($30)
  
• One shorted 12R wire along radiator support caused by auxiliary battery hitting the radiator support wall. The auxiliary battery tray has rusted away which will not allow battery to be secured
• Action: Replaced Wire. ($8)
• Action: New auxiliary battery tray fabricated ($50)
  
• Two headlights burned out
• Action: Replace ($40)
  
• One more headlights burned out
• Action: Repair problem before replacing

[72lb4x4]

I'd guess that the regulator isn't working right. Measure the voltage at the battery with the engine off, and running at various RPM, such as a 1000, and 3500 where it seems to fry the headlights.

An electronic regulator is available that supposedly works better than the OEM style mechanical reg.

[Jtrux]

I didn't read all posts so I don't know exactly what's been said, if i'm repeating something, i'm sorry. Personally when I have charging problems I start with the alternator. Whether it's internal or externally regulated I will take it to get it tested. Then work your way to the voltage regulator. They can test these as well. All wires coming to the alternator, regulator, battery and any imbetween are checked. I had a HUGE problem with my charging system that no amount of trouble shooting could fix. I called LMC and ordered the front portion of the wiring harness, the one that goes from the firewall to the alternator, battery and headlights and I haven't had a problem since. I guess I just had bad wiring, might be your problem as well.

Like I said, I would take the time to get the alternator and regulator checked regardless of when you purchased them. As far as the internally regulated alternator goes, i'm a believer in them. By putting one on you really don't do anything to the blazer that can't be reversed. It'll cost more but it might just be worth it to you. If you go the internally regulated route, make a new thread and i'm sure someone will gladly tell you how to wire it up, nothing dificult or permanent at all.

[Green Monster]

It only took 11 months but I finally put this issue to rest. I took my blazer to a automotive electrical repair shop: Keystone Auto Electrical.

The problem was a burned out voltage regulator and a bad alternator. I had replaced the voltage regulator prior to bringing it to Keystone Auto Electrical but it was apparently the incorrect kind and had already burned up. I had installed an electronic voltage regulator when the correct part is a mechanical voltage regulator. I did not know there was difference. The Blazer runs great and I am happy to have it back on the road. Thanks for your help guys.

[Critter]

Glad to here that one of my favorite blazers is back in action (I think I like your more than I like my own ) Now if we can just get those d@mn scammers to leave you pics off the web...

[65-72 chevytoys]

Can a parts store like NAPA or Autozone test an external voltage regulator? I have been having a similar problem with the fuse link at the battery burning through because the red wire got so hot. With the ignition off I have twelve volts in the red wire. I cant keep the engine running long enough to test it running to see if there are any voltage spikes.

[Jtrux]

Originally Posted by 65-72 chevytoys

Can a parts store like NAPA or Autozone test an external voltage regulator? I have been having a similar problem with the fuse link at the battery burning through because the red wire got so hot. With the ignition off I have twelve volts in the red wire. I cant keep the engine running long enough to test it running to see if there are any voltage spikes.

Yessir