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Old 02-21-2011, 10:02 PM
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92 k15 full size blazer elec problems

Ok guys here's the low down. Ive been having some odd electrical issues with my 92 k15 full size blazer. Initial red flags were while running my head lights if I turned on my heater my speedometer would bury itself at max. Also when i turned on my blinkers my speedometer would jump up and down. The deal breaker was when I was cruising down the free way at 11 pm my headlights went out completely. I quickly began trying to sort the issue out inside my cab at 60 mph and i turned on my heater. The headlights then came back on. I should also add that although my headlights went out my engine never died nor did it sputter. SO I think I have a ground issue OR I may have a bad alternator that just went **** up, but im leaning more towards a bad ground. I replaced the toggle switch for the head lights and got a weird result. If I turned on my headlights (after I installed the new switch) my heater display screen would black out. I could still control the heater ie. turn it off and on and adjust fan speed, tempreture and flow route but the screen just went black, and it would light back up when I turned the headlight off. Also the heater control unit made a weird clicking kind of noise when the headlights where on. Ok so here's what I've done to trouble shoot it. I looked at my headlight grounds,they looked ok,I looked at my audio system grounds,also looked good and I looked at my alternator ground,which there doesn't really seem to be one so im assuming its grounded directly to a bracket which is in turn grounded to the frame via the main engine ground strap. Now as far as my main ground strap is concerned it goes from the back of my block to the fire wall then a seperate strap is bolted to the same bolt and then goes to the frame on the passenger side. As far as i can tell that ground strap looks good but the bolt that is holding to the engine has oil and gunk all over it. I know this is a long post but im trying to give everyone all the details so you can help me out. Ok last thing I did to trouble shoot it is I fired up the truck and then disconnected the battery which caused the truck to instantly die which leads me to believe the alternator is bad. Ok so if the alternator is bad would I have all those electrical problems? If its the main engine ground can I just re ground it where ever I want and if so do I need to go engine to firewall to frame or can i go engine to frame. Have at it guys and thanks alot. You can also send me emails at ashshaynesyd@yahoo.com and title them blazer help. Photos are great if u got em lol. Thanks again.

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Old 02-22-2011, 04:59 AM
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If the Alt is bad, which you have indicated, I'd replace that 1st and see if the problem goes away. My advice is to tackle one problem at a time.

When you say the grounds look good, how did you detirmine that? Bare metal to metal contact is a good ground, metal to rust isn't.
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Old 02-22-2011, 06:01 PM
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I would bet the ground from the firewall to the head is rotted off and the ground is being pulled through other devices.
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Old 02-22-2011, 06:08 PM
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Bulkhead wiring, all day long. Had it before,easy to check turn everything on have a buddy watch the lights and grab a hank of wiring next to the bulkhead connector and wiggle. Betcha you find it there.
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Old 02-22-2011, 06:23 PM
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I agree with the bulkhead connector
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Old 02-22-2011, 07:27 PM
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ok?

So when you say bulk head wiring,do you mean the ground strap from the fire wall to the engine block or what,I hate to sound inexpierienced but this problem is a tough one for me so I just want to make sure im getting your suggestions right before I begin to address each one.
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Old 02-22-2011, 08:37 PM
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The bulkhead connector is where the wires from the engine bay pass thru the firewall into the fuse box. Sometimes there is 1 or 2 screws that hold the connector to the fuse block etc..... since it is a connector, they sometimes get corroded etc..
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Old 02-22-2011, 09:25 PM
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found it,no problems.

I found the spot where it all plugs in and I did the "wiggle" test, no signs of any issues at that point. Do think that a ground strap can go bad just due to age? As I said it looks to be intact and the only thing I think may be causing an issue with the ground strap is all the oil and gunk build up on the bolt that holds it on to the block.Other then that I cant find any thing else that may be causing it besides the alternator being bad. And I still dont see how a bad alternator would cause all those problems that ive been having
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Old 02-23-2011, 08:08 AM
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An easy test for the ground is to take a jumper cable and connect it from the negative battery cable to the body somewhere and see if the issue goes away.
Thinking back I had one of those that the harness that runs across the front of the truck to feed lights got damaged and it caused all kinds of weird issues. Runs in front of the radiator
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Old 02-23-2011, 08:24 AM
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X2 on using a jumper to ground a circuit for testing. Be sure the connections are made to bare metal.

Removing the battery terminal isn't a check for the alternator output, and can damage the alternator, so don't do that anymore.

You mentioned at one point the headlights went out. This is almost always because the circuit breaker tripped, causing the lights to go out until the breaker cooled down enough to reset.

This can be caused by a bad headlight switch or just the ground for the switch, and because initially the speedometer was involved (electric speedo, I'm going to say), this probably points to the ground being shared by the headlight switch and the speedo (and possibly the HVAC display as well).

I would start looking under the dash for any grounds that would go between the cluster and a metal brace, etc. adjacent to the cluster. Then continue to the ground straps you mentioned, ending up where ever the last headlight ground is located.

If you still find nothing, the switch could be the culprit.
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Old 02-23-2011, 11:50 AM
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I would take e a real hard look around the "Audio System" to make sure something didnt get disconnected during the install process. If I remember correctly there is a ground stud on that cluster to the left of the wheel up high. Everything that is not working is somehow attached to the cluster controls.
Find it and make sure the ground is still attached. It seems they had a habit of coming loose
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Old 02-23-2011, 05:09 PM
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Ground sounds like the right way to go
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Old 02-23-2011, 09:53 PM
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update

First off let me just say that you guys are all awesome and I appreciate all your input. I have found the problem and fixed. Since you are all car guys im guessing you all want details . Ok so cobalt i had already replaced the switch before you made your suggestions because obviously replacing a switch FIRST is much easier then doing all the stuff you suggested first lol. So it wasnt the switch. It was however the last ground leading from the head lights to the fended body. After I did the wiggle test that latech suggested I decided to do that to a bunch of other stuff. So when I wiggled that ground wire from the headlights the truck instantly died. BINGO. So what i did was unhooked it cleaned it up with a solvent then electical connection cleaner then i lubed it up with white grease (electrical connection grease) and it was p[roblem solved,no speedo jump,no surge when running lights heater blinkers nothin. Also when I turned on my headlights my heater control screen stopped blacking out. I also went through after that and replaced every ground strap I could find and of course lubed up all the new ones and the battery terminals and all the switch contacts got greased to. Unattached the bulkhead wiring pack and cleaned and greased those connections so im solid now.Thanks again guys.
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