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Old 07-31-2018, 08:26 PM   #1
bsager79
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1972 blazer electrical problems

Im new to the site and tried searching to see if this issue had been covered but the search option wouldn't work.
I have blinker, hazard, brake light, and back-up light problems.
When switching the blinker in either directions all of the blinkers light up. When i apply the brake and hold it all blinkers light up. Hazards dond seem to do anything. The back-up light fuse was missing, but when i put a fuse in it the started flashing rapidly.
Im lost. Everyone tells me its a bad ground but i dont have a clue where start.
Thank you in advance to anyone who can help.
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Old 07-31-2018, 10:31 PM   #2
billthompson
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Re: 1972 blazer electrical problems

i would start here

http://outintheshop.com/faq/wiring/wiring.htm

you may need to click on a link when themsite comes
up.

most if not all the lights you are speaking of use the body itself as ground so id think if
they are working at all your ground is good. my best guess is there is a short connection between one of the blinker wires and the others and id guess that is
in one of the connectors coming out of the cab or the harness itself has rubbed up against something. the wiring in these trucks is pretty simple. also, if someone has added a trailer light connector might be another place to look. id suggest finding and tracing all the
wiring harnesses. just find them and visually check everything over. then get back with us with what you find
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Old 07-31-2018, 11:36 PM   #3
Greenlee
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Re: 1972 blazer electrical problems

A bad ground can do weird stuff like that. When I replaced my wood bed the lights started acting up. Putting a ground strap from the frame to the bed fixed it.
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Old 08-01-2018, 08:17 AM   #4
jaros44sr
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Re: 1972 blazer electrical problems

Have you replaced the blinker module on the fuse block, while your under there it might be a good time to replace your horn relay(I've heard these fail and melt your harness)


good luck and keep us posted on your findings


we need pics of your truck and welcome aboard
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Old 08-01-2018, 12:30 PM   #5
paul mora
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Re: 1972 blazer electrical problems

I would start with checking each light a verifying that it turns on when it get power. Start by turning on the lights. That tell you the bulbs are ge some power and are grounded then go to the turn signals that will agin tell you if that bulb has power. If all that works pull the flasher and test the brake lights and turn signal. That will tell you that circuit is fine or the flasher or flasher switch is bad.
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Old 08-01-2018, 01:55 PM   #6
Utahboy
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Re: 1972 blazer electrical problems

I recently had a similar issue after putting everything back together form a complete tear down. I found the issue was that the circuit panel on the back of the gauge cluster was not completely grounded. There are certain screws that ground the circuit panel to the back of the Cluster. Some of the screws were not completely tight resulting in issues with the turn signal indicators not working properly.
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Old 08-01-2018, 09:17 PM   #7
bsager79
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Re: 1972 blazer electrical problems

Thank yall for the advice. I have tried damn near everything yall proposed. The only change is the speakers no longer thump in unison with the blinkers.
All of the blinkers still blink when engaged in either direction. Hazards do nothing unless the blinkers on and then turning on the hazards kills the blinkers.
Back up lights still flash with truck in park when i install the fuse. I found a few bad spots in the wire along the frame and replaced all the wires from the firewall to the rear plug. I thought that was it, but wrong.lol. Thanks again for the advice. Im gonna keep tinkering.
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Old 08-01-2018, 11:42 PM   #8
billthompson
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Re: 1972 blazer electrical problems

id be happy to share the techniques i use to trouble shoot electrical problems if you want. like i say the wiring on these trucks is pretty simple. hopefully your trucks wiring is stock or
close to it. if so it should be a snap to figure this out.
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Old 08-01-2018, 11:45 PM   #9
bsager79
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Re: 1972 blazer electrical problems

Ive been studying the diagram you sent. Thank you. It seems pretty clean but i believe my problem is around the fuse box. There are alot of wires going nowhere.
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Old 08-02-2018, 12:36 AM   #10
billthompson
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Re: 1972 blazer electrical problems

yep thats where it almost has to be. if you checked the basics like bonding wires and damaged harnesses then the most logical place to look is under the dash.the part of your problem that makes it challenging for me is the back up
lights. they arent part of the signal light circuit at all. and you said the speaker was making noise?. if you double checked bonding grounds then you might look for damage under the dash and steering column
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Old 08-02-2018, 09:17 AM   #11
billthompson
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Re: 1972 blazer electrical problems

post some pictures of your under dash wiring and ill see if i can spot anything
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Old 08-02-2018, 09:58 AM   #12
bsager79
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Re: 1972 blazer electrical problems

👍will do. Its a rats nest.
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Old 08-02-2018, 10:46 AM   #13
billthompson
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Re: 1972 blazer electrical problems

the last guy didnt do you any favors. i see several modifications. most of that stuff hanging and unhooked is wrong and could be a source of your problem. you may have better luck fixing it if you take it out of the truck. trust me. it really aint that hard. i prefer to have it on my bench so i can go wire by wire. thats what i would do at this point.
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Old 08-02-2018, 10:57 AM   #14
billthompson
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Re: 1972 blazer electrical problems

whats that thing off to the left on the kick panel
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Old 08-02-2018, 11:30 AM   #15
bsager79
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Re: 1972 blazer electrical problems

I was thinking its some thing to do with the ignition. The truck has a big block and theres not alot of room under the hood.
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Old 08-02-2018, 12:36 PM   #16
billthompson
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Re: 1972 blazer electrical problems

im assuming your truck starts and runs. does your truck have a column shift either automatic or 3 speed? im asking because i see a pair of purple wires in a plug under the steering column. i think thats suppose to be hooked to your neutual switch down on the column to keep the truck from starting unless its in park or neutral. i also see dark green wires hooked to that hanging flasher. one thing dark green is for is backup lights witch is also hooked to the neutral switch of a column shift truck. i can only go off what i can see so i can be wrong but i think that might be another place to look
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Old 08-02-2018, 01:06 PM   #17
billthompson
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Re: 1972 blazer electrical problems

im almost confident somebody has put the hazard flasher in the plug with the green wires instead of where its supposed to be in the upper left corner of your fuse box. that would probably explain why your back up lights flash and your hazards dont work
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