Both headlights burned out tonight... Why?

[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

[65-72 chevytoys]

Thanks. I will have to take them out, but I will go and get them tested.