Both headlights burned out tonight... Why?

[red71cheyenne]

The gas guage is usually indicative of a bad sender or an open wire. Could be the ground on the dash harness is loose. As far as checking for amps, you need to check it the way the drawing is. Thru an open in the circuit. If you try to read voltage there, it won't read right. Read voltage across the line, like with the ground cable connected. Looks like your dash lights and gas guage might either be affected, or part of the problem. I know you said you headlight switch wasn't bad, but do you have a spare you can plug in to check it? Jeff.

[72lb4x4]

Sorry to say this, but I've gone back and read each of green's posts, and its apparent you don't know how to use your meter, or the difference between voltage and current.

You state that you connected the voltmeter between the neg batt terminal and cable and read 12V. That's how you connect an ammeter. 12V would be a normal reading with that connection if even a minute amount of current is drawn with the key off.

You also state that you have a 12V "draw." A load draws current not voltage, so this is meaningless.

You're original post is for possibly burned headlights and it somehow morphed into a key off drain.

Don't change problems in mid-disaster. Also, don't rewire anything until you know what the problem is.

If you suspect you're headlights burned out, test their resistance.

If you suspect a current draw while everything is turned off, you might try disconnecting the wiring harness connector at the firewall. It bolts on under the hood by the master cylinder.

Test again with the light, or with an ammeter connected where the light was.

What is the current drawn?
What is the voltage on the battery with the engine running and off? This is more to give an indication of the battery/charging status.

What is connected to the junction block where the small positive wire from the battery on the fender? Normally there's a red and black wire there that go into the wiring harness, accross the core support, and so on. Other wires indicate creative wiring. See the wiring diagram:

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

If your light goes out with the firewall connector disconnected, the problem is under the hood. If not, try disconnecting the read and black wires from the junction on the fender one at a time.

If current is still flowing with both wires disconnected from the junction, something is strange ;(

The fusible link by the battery in the diagran is supposed to stop the carbecue, BTW...

[old man jimmy]

I agree. This whole thing started out with blown headlights. If you are describing your problem acurately. I still say Voltage regulator. And a slim chance of shorted cell in battery, The altinator supplies the juice, but the voltage regulator tells it how much to supply. But if you have a shorted cell, it can fool the regulator into thinking it needs to put out more juice. It's that simple.. A new regulator cost $16,00 at autozone, and they have them in stock. Takes 5 min. to put one on. Less time than it will take you to write your next post. As far as the battery goes. Your getting 12+ volts. But no load test. You can get 12 volts from a flashlight battery, but it won't start a truck. And if your battery is 4 yrs. old, it's probably at the end of it's life. I rarely get 4 yrs. from one. Especially one that's used very little, as I suspect your truck is. At the very worst, you'll end up with a spare regulator for your truck. A battery, you can always borrow from one of your others for testing. When you've worked on old iron as long as I have, you learn there are no guarantees. You take the most logical first, and if that don't solve it, you go on to the next. Just don't bulldoze the whole yard to get rid of a weed. The more you play & tear things apart looking for your problem, the more likely you are to create more problems. Just my opinion, but it may be better if you take it to someone who really knows what they are doing. And may be cheaper in the long run. You have too nice a truck to wire & gum back together.

[Green Monster]

I installed a new voltage regulator. Battery is charged at 12V. Engine cranks but will not start. Battery still drains about 1 volt an hour. Looks like this thing is more messed up than I anticipated. I have a new headlight switch too and was going to install it once I tested the headlights but I can't even get the Blazer to start now.

[jaros44sr]

See if your getting voltage to the coil. Are the spark plugs firing?

[Green Monster]

Originally Posted by jaros44sr

See if your getting voltage to the coil. Are the spark plugs firing?

I pulled one spark plug wire, put a screw in it and placed it on the frame. Then turned the engine over. No spark was observed. Then I put the wire back onto the spark plug.

I placed my volt meter inline of the coil wire (the wire that goes to the center of the distributer cap) then turned the key. I did not attempt to turn the engine over, I just turned the key clockwise until I heard that click that I usually hear before I start the engine. I checked the voltmeter and no voltage was being read.

What does this mean? Is my coil fried?

[jaros44sr]

Originally Posted by Green Monster

I pulled one spark plug wire, put a screw in it and placed it on the frame. Then turned the engine over. No spark was observed. Then I put the wire back onto the spark plug.

I placed my volt meter inline of the coil wire (the wire that goes to the center of the distributer cap) then turned the key. I did not attempt to turn the engine over, I just turned the key clockwise until I heard that click that I usually hear before I start the engine. I checked the voltmeter and no voltage was being read.

What does this mean? Is my coil fried?

I'm glad you didn't crank it, as that spot you picked could make 60,000 volts
I was kinda thinking you had a power surge from your coil blowing, sending current to the bulbs, but what do I know I'm a newb

See if you get voltage going to the coil[+] side. Turn the key to the "on" position. If there is 12volts to the coil, then my guess is time to replace it. If you don't have 12 volts look back down that wire, till you do get 12volts. I don't have my wiring diagram in front of me, so I can't tell you color or where it comes from...

Hope it is the coil since that is an easy fix.... JMHO J.

[old man jimmy]

If you want to test for spark. You can't actually touch it to the frame. You just grounded that plug. I usually stick a phillips in the spark plug boot, and hold the metal blade of screwdriver about 1/4 in. from any good ground. Have someone else grind the starter, and see if you get a spark jump from blade of screwdriver to ground, If so you are getting fire to the plug. If not check voltage to coil as stated. But if your coil crashed when your lights went out, you wouldn't have drove it home in the dark as stated. One other thing, make sure your phillips has a good handle on it, or you will get bit. If that bothers you, just pull a spark plug wire, push a spare plug into it, and ground the plug to see if you get spark when someone esle cranks it. Good luck guy. Just noticed a typo (I think) on the above post. You must have 12 volts to + side of coil when key is on. And the wire goes from ignition switch to + side of coil. - side goes to dist.

[jaros44sr]

Originally Posted by old man jimmy

If you want to test for spark. You can't actually touch it to the frame. You just grounded that plug. I usually stick a phillips in the spark plug boot, and hold the metal blade of screwdriver about 1/4 in. from any good ground. Have someone else grind the starter, and see if you get a spark jump from blade of screwdriver to ground, If so you are getting fire to the plug. If not check voltage to coil as stated. But if your coil crashed when your lights went out, you wouldn't have drove it home in the dark as stated. One other thing, make sure your phillips has a good handle on it, or you will get bit. If that bothers you, just pull a spark plug wire, push a spare plug into it, and ground the plug to see if you get spark when someone esle cranks it. Good luck guy. Just noticed a typo (I think) on the above post. You must have 12 volts to + side of coil when key is on. And the wire goes from ignition switch to + side of coil. - side goes to dist.

Good point, I forgot he drove it home, so it has tobe something he did in the garage. Please go back and check all your connections, maybe one was put on loose.

How could I forget the coil wire goes to the switch, must be CRAFT... J

Ignition switch sounds like the culprit now, check it out...
Great thing about this board, if you give wrong advice someone is there to correct the situation!!!

[pound41]

When I brought home my 70 Blazer it had numerious wire hackerys. Toggle switch to start the compressor. Pigtailed wire to run the distributor. The ac switch was melted. Headlight switch had been hot. Printed ciruit had been hot. Anyway, it appeared that when it had a wiring issue. They just used country engineering and pigtailed wires off new sources etc. I went through and corrected all the problems. New ac harness etc. I was also driving it some during the corrections. I put on a new carb and start it up and the main wire harness where it sits behind the Drivers fenderwell goes up in smoke all the way across the front to the junction box. When I removed the burnt harness from behind the fender well you could see where one wire had rubbed through the insulation and had grounded out and shorted out the rest. I replaced all the burnt wires and never had a problem since. my guess was the insulation had worn and when it virbrated on to the metal it would short open circuits

[Green Monster]

Originally Posted by pound41

When I brought home my 70 Blazer it had numerious wire hackerys. The ac switch was melted. Printed ciruit had been hot. Anyway, it appeared that when it had a wiring issue. They just used country engineering and pigtailed wires off new sources etc.

I have had this issue. I have found a few wires that were cut off and just laying there. It is a bit of a mess.


I had my dad hold the plug wire with a screw coming out of it near a grounding point. He held it with a pair of insulated pliers. I cranked the engine and no arc or spark was observed.

When I hook the battery up it drains down slowly. About a volt an hour. This was happening before I even touched any wires. Sounds like I have multiple problems here. I think this is meant for a "professional."

[jaros44sr]

Hey you gave it your best shot, no harm no foul... J.

[Green Monster]

Originally Posted by jaros44sr

Ignition switch sounds like the culprit now, check it out...
Great thing about this board, if you give wrong advice someone is there to correct the situation!!!

How do you determine if the ignition switch is bad. Is this the switch at the dash where I insert the key?

[jaros44sr]

Originally Posted by Green Monster

How do you determine if the ignition switch is bad. Is this the switch at the dash where I insert the key?

Yes on the location, and all you have to do is check volts going in and volts going out. Therefore, if current goes into it, it must come out. Think of a switch as one wire cut in half, all it does is rejoin a cut wire allowing current to flow on. I don't have an ignition switch in front of me but, power[12volts] comes into it, and goes out to feed the coil...J.

Haven't quite given up yet??? atta boy

[old man jimmy]

You didn't say if you have 12 volts at + side of coil with key on. Let us know that before you tear into the ignition switch. Don't get the cart ahead of the horse. As far a your headlight switch. You don't need to have it running to check it. Everything on your switch works the same, key off or key on. If you have 12 volts to + side of coil wire. Pop your dist. cap and make sure your points are opening. If you've been doing a lot of testing with key on and the points happen to be shut, they could have melted together. Old point type dist. do that. That's why they use to have an acc. side to the ignitions switch if you wanted to listen to the radio with engine off. With the key turned to acc. side the points are cold.

[Green Monster]

I popped the distributer off. The points are not melted. It looks good inside. The rotor looks good too. I checked the positive side of the coil. I pulled the two wires that were connected to the driver side (is this the positive post?) and placed my volt meter between the post and wires that were connected to it. Turned the key on and no volts. I still have a drain on the battery. I checked the other post on the coil just to be on the safe side. No reading there with the key on either.

I disconnected my headlight and disconnected my radio and check for a drain on the battery. I still have a drain on the battery.

I am guessing my ignition switch is the culprit... but I cannot get the wire harness disconnected. How does this thing come off? I see two plastic tabs and I'm pushing them in and pulling the harness toward the firewall. Am I doing this right?

I saw this thread for removing an ignition switch... http://67-72chevytrucks.com/vboard/s...light=ignition
I can't this to work either. I just want to unplug the harness from the back.

[72lb4x4]

Sorry if my earlier post was a bit blunt...

My statement in quotes below is backwards/inaccurate. If the light goes out (current flow stops) the problem is likely to be in the cab or wiring going to the rear of the truck.

"If your light goes out with the firewall connector disconnected, the problem is under the hood. If not, try disconnecting the read and black wires from the junction on the fender one at a time."

You can also disconnect the harness connector at the outer firewall that goes toward the passwnfer side. Then reconnect the connector that runs along the driver's inner fender. Check current flow from the battery. If its zero or close, check the disconnected part that runs toward the alternator, powers the solenoid for cranking, etc. Current still flowing suggests a drain in the cab.

Disconnecting big chunks of the system as described is a good way to get closer to the problem without a lot of work/suffering.

If the truck cranks, and the accessories work with the key on, I'd guess the ignition switch and associated wiring is ok.

In a negative ground system such as this, voltage measurements are made from some point (such as the + side of the coil), to ground. Ground should be but isn't always (due to bad grounds), the frame, body, or almost any metal part.

Voltage is not measured in series as you describe you are doing.

You might try disconnecting the small plug connector at the alternator, testing current flow (Amps), then if no change, disconnect the large red wire to the alternator, and testing current again.

A one Volt drop per hour on a known good battery is a lot! If that much current is flowing, your test light would fry. In a weel ventilated area, with all accessories off, the key off, the door closed, etc., if you remove the negatie battery cable and touch it to the negative battery post, do you get a good bunch of sparks? No suggests:

Maybe a bad battery? Have it tested...

If you have a timing light, try checking for spark with it. If it lights, you have spark. Now you need "gas." Open the throttle and shoot some carb cleaner into the carb. Try to start. If it fires and dies, it needs gas.

Sorry, that was long winded... Good luck!

[old man jimmy]

You need to go back and check the coil for voltage again. You can't do it the way you did. Hook the black wire of you tester to a good ground, then hook the red wire to the + side of the coil, then turn the key on & see what you get. On top of the coil they are marked + & - by the posts. Drivers side means nothing, as it's probably been turned in the bracket a dozen times. Just look for the + and hook the red wire of your tester to it. No point messing with your ignition switch till you find this out. You need to learn how to use your voltage tester.

[old man jimmy]

72 4X4 beat me to it. But as I said way back. The more you tear apart the more likely you are to create other problems. It's obvious your not a mechanic. I suggest first off you find out why it wont start. Forget your battery drain for now. The problem could be one and the same. But a lot easier to track down your starting circuit first. I repeat.. One thing at a time. It kinda scares me when you talk about disconnecting this and that, like radio etc. You drove it home & parked it. It was running then. You kinda got a one track mind, when it comes to your "voltage drain" I wish you'd just put everything back the way it was when you got it home, & we'll go from their. I was a mechanic at a Ford dealership for years, and I can't tell you how many cars we got in that people tried to fix themselves, and didn't know what they were doing. Only makes a small problem into a big one. I am glad you describe how you are testing things. If we just assume you're testing it right, and you're not. We're up a creek on giving advise. And yes I would keep your battery cable off while you're not their till we get this worked out.

[Green Monster]

Thanks for the advice. I appreciate it. I really do. I'm learning as you teach me. I will follow the advice you guys gave me. As requested, I will connect my headlight switch and radio then get started with the checking the coil again this afternoon after work.

[Green Monster]

Originally Posted by old man jimmy

You need to go back and check the coil for voltage again. You can't do it the way you did. Hook the black wire of you tester to a good ground, then hook the red wire to the + side of the coil, then turn the key on & see what you get. On top of the coil they are marked + & - by the posts. Drivers side means nothing, as it's probably been turned in the bracket a dozen times. Just look for the + and hook the red wire of your tester to it. No point messing with your ignition switch till you find this out. You need to learn how to use your voltage tester.

I followed these exact instructions: Black wire to a bare bolt on my engine. Red wire to the + side of my coil. Turn key on with battery connected. No voltage is showing on my meter.

[jaros44sr]

Originally Posted by Green Monster

I followed these exact instructions: Black wire to a bare bolt on my engine. Red wire to the + side of my coil. Turn key on with battery connected. No voltage is showing on my meter.

Dbl. check that your meter is working on some known voltage source, like the battery.

Doesn't look like the coil, ign. switch???? JMHO J.

Wierd tho, can't figure how you drove it home

[Green Monster]

Okay! I got her started and running again! I'm so excited. I had to do some wire tracing...

I traced a brown wire out of the from my firewall to my gas tank. Then I went back to that brown wire at the firewall and traced it into my passenger cabin. It was just floating in front of my fuse block. I plugged it into the open slot and walla! My gas gauge came back to life. I followed my + ignition coil wire to my firewall and found I had it plugged into my radio slot. I plugged it into the slot that reads "un-fused". Plugged the radio into the radio slot. Turned the key she started right up.

Now, I still have this drain on the neg. side of the battery that was an issue before I touched a single wire. Hmmm...

[Green Monster]

Originally Posted by 72lb4x4

Sorry if my earlier post was a bit blunt...

My statement in quotes below is backwards/inaccurate. If the light goes out (current flow stops) the problem is likely to be in the cab or wiring going to the rear of the truck.

"If your light goes out with the firewall connector disconnected, the problem is under the hood. If not, try disconnecting the read and black wires from the junction on the fender one at a time."

You can also disconnect the harness connector at the outer firewall that goes toward the passwnfer side. Then reconnect the connector that runs along the driver's inner fender. Check current flow from the battery. If its zero or close, check the disconnected part that runs toward the alternator, powers the solenoid for cranking, etc. Current still flowing suggests a drain in the cab.

Disconnecting big chunks of the system as described is a good way to get closer to the problem without a lot of work/suffering.

If the truck cranks, and the accessories work with the key on, I'd guess the ignition switch and associated wiring is ok.

You might try disconnecting the small plug connector at the alternator, testing current flow (Amps), then if no change, disconnect the large red wire to the alternator, and testing current again.

A one Volt drop per hour on a known good battery is a lot! If that much current is flowing, your test light would fry. In a weel ventilated area, with all accessories off, the key off, the door closed, etc., if you remove the negatie battery cable and touch it to the negative battery post, do you get a good bunch of sparks? :

Yes, your previous response was a bit "blunt". I can get over that. I prefer blunt over no help at all. I don't claim to be a mechanic or an electrician. I do claim to be persistent. I do want to learn. However, I do appreciate your help, and everyone else's help as well. I have a few questions and comments about your statements.

1. How do I disconnect my firewall connector? Is it one plug or a series of smaller plugs, or neither? I took a picture of what I think you are talking about.

2. When connecting the ground cable to the battery, I do get sparks.

[jaros44sr]

That single bolt in the middle of the connecter has to be unsrewed, but it may not come all the way out. Sometimes they have a retaing clip that keeps the bolt from dropping all the way out, not sure...anyway loosen the bolt and you should be able to pull the connecter straight out.

Don't know where he is going with the neg. sparks, but it sounds like a short in a ground. J.