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Car stereo problem

Onebad68

Onebad68

Kind of a big deal
Joined
May 19, 2020
Member Number
189
Messages
61
Loc
Hermiston, Oregon
I have a 1968 Shortbox chevy 2wd c10. It was a frame off everything replaced/upgraded including a new aftermarket blade fused wiring harness. I modified the dash, shaved the ashtray and installed a double din touchscreen stereo with navigation and backup camera. Full on infinity component speakers, amps and subs. Stereo works great if you turn the key to ACC or ON everything works as it should. Start the truck and everything goes off. I have 13.5 volts when running and have 13.5 volts on the red and yellow ACC wire and constant power, I am also getting a good ground. Turn the key off, kill the motor and put the key back to on or ACC and everything comes on as normal.

Has anyone ever heard of this? I have no idea where to start since it is getting both 12v inputs and ground????
 
Last edited:
Does the start pos of the ign switch kill the acc power or does it keep the acc feed powered?
 
^ Might be the ignition switch killing accessory power upsetting the head unit. What brand head unit are you running?
 
92 s dime said:
Does the start pos of the ign switch kill the acc power or does it keep the acc feed powered?
Click to expand...

I just uploaded a video of it doing it.


Yes it does when cranking, all the factory 67-72 switches are the same. I am running a dual stereo, I know it’s not great but it was the only one I could find at the time with a bezel to cover the hole around the stereo.
 
Ted_Kaczynski said:
Only thing changing between running and not running is alt. Charging.
Click to expand...


I forgot to mention I even unhooked the alternator to rule that out. I am completely stumped on this, I have even tried starting it quick and not giving it a chance to start powering up before the starting circuit drops again he power out.
 
M92PV4U said:
Where do you have your ground connected?
Click to expand...

I have a common bolt on the firewall for everything in the dash. I have a braided ground strap from firewall to valve cover stud, #4awg copper from frame to body, #4awg engine to frame, 2/0 battery to same stud on engine. All of them are good and clean, this has about 5 miles on it since the rebuild.
 
I thought the ground might be switching polarity when you start the engine but it doesn't sound like that is the problem.
 
Try this
turn the key from acc to off and back fast like you would if you were starting it
start the engine and then apply power to the red wire
 
so we're currently thinking that it's just the low voltage during cranking that causes this or it's the key switching the power off momentarily right?

what happens if you hot wire it directly to the battery and then start the truck?

if it's just the voltage drop it should behave similarly. a capacitor could probably fix it.

if it's actually getting shut off at the key, rewire it.
 
87manche said:
so we're currently thinking that it's just the low voltage during cranking that causes this or it's the key switching the power off momentarily right?

what happens if you hot wire it directly to the battery and then start the truck?

if it's just the voltage drop it should behave similarly. a capacitor could probably fix it.

if it's actually getting shut off at the key, rewire it.
Click to expand...

Thats the thing I cant wrap my head around, you can turn it to run or ACC and it will powere up, turn it to off and back to run or ACC and it comes on, Once you go to start and the key goes back to run it will not turn on, I have verified good ground, constant and switched power at the back of the unit while running and get 13.5volts on both along with a good ground. I do have a 2.0Farad capacitor for the amps behind the seat I could tie into but feel like that is a bandaid. This is going to drive me crazy not being able to pinpoint the root cause.
 
Been a while since I've been in a GM of any sort...

Is RUN a separate circuit from ACC in that vintage? Are other things that are wired to ACC working correctly?
 
Onebad68 said:
Thats the thing I cant wrap my head around, you can turn it to run or ACC and it will powere up, turn it to off and back to run or ACC and it comes on, Once you go to start and the key goes back to run it will not turn on, I have verified good ground, constant and switched power at the back of the unit while running and get 13.5volts on both along with a good ground. I do have a 2.0Farad capacitor for the amps behind the seat I could tie into but feel like that is a bandaid. This is going to drive me crazy not being able to pinpoint the root cause.
Click to expand...

backprobe the radio connector and see what the fuck actually happens to that circuit when you start the car.

I built a cheapo o scope kit so I could easily see shit like that.
 
rockota said:
Been a while since I've been in a GM of any sort...

Is RUN a separate circuit from ACC in that vintage? Are other things that are wired to ACC working correctly?
Click to expand...

what he said.

I'd put a multimeter on the acc wire and start the truck to watch what happens.

If nothing changes there, I'd start the truck and check the constant power wire for continuity.
 
Does the head unit have a rem input? It's usually a blue wire rem out to trigger power to amps and such after the head unit is powered up. Does your head unit have a rem input that's wired wrong or something?
 
rockota said:
Been a while since I've been in a GM of any sort...

Is RUN a separate circuit from ACC in that vintage? Are other things that are wired to ACC working correctly?
Click to expand...

I have it wired as the same circuit, it’s got an aftermarket wiring harness in it
 
87manche said:
backprobe the radio connector and see what the fuck actually happens to that circuit when you start the car.

I built a cheapo o scope kit so I could easily see shit like that.
Click to expand...

acc power drops out while cranking but instantly comes back after cranking
 
Ted_Kaczynski said:
Does the head unit have a rem input? It's usually a blue wire rem out to trigger power to amps and such after the head unit is powered up. Does your head unit have a rem input that's wired wrong or something?
Click to expand...

Here is what I am working with. It does have a remote for the amps, they are not powering up either when it’s running

A27F7399-692A-4727-AA39-41729D3853E5.jpeg
 
Onebad68 said:
I have it wired as the same circuit, it’s got an aftermarket wiring harness in it
Click to expand...

I think you need to doublecheck that.... it really sounds like you’re shutting power off, especially since it’s happening to the amps as well.

what happens if you put the key in RUN but don’t start the truck?
 
Onebad68 said:
acc power drops out while cranking but instantly comes back after cranking
Click to expand...

and your cheap radio obviously doesn't like that.

move the power to a circuit that remains on during cranking.

I don't understand how you frame off restored this truck and installed amps and speakers and decided to go with a $150 walmart head unit.
 
rockota said:
I think you need to doublecheck that.... it really sounds like you’re shutting power off, especially since it’s happening to the amps as well.

what happens if you put the key in RUN but don’t start the truck?
Click to expand...

It does shut power off for about a second, it has a sniper fuel injection unit on it and pops off right away when starting. I cant replicate this when switching from RUN or ACC to off and back simulating the Start-Run sequence. If I put it from Off-Run it works great it only starts acting up from the run-start-run sequence. I have built a 67 SWB, 67 LWB 4wd, 72 Jimmy and a 72 blazer- same wiring harnesses and wired the same way with no problem. My 3rd gen dodge has a nice pioneer in it and it shuts off while cranking but comes right back on like every other vehicle I have had an aftermarket stereo in.
 
87manche said:
and your cheap radio obviously doesn't like that.

move the power to a circuit that remains on during cranking.

I don't understand how you frame off restored this truck and installed amps and speakers and decided to go with a $150 walmart head unit.
Click to expand...

Read above, It was the only radio I could find at the time that had a bezel/trim ring in a double din. Everything else has a plastic install kit to put in a new car. I even had to go to a local stereo shop to find a double din "cage" to mount it in the dash as most all the new head units dont come with them .
 
Onebad68 said:
It does shut power off for about a second, it has a sniper fuel injection unit on it and pops off right away when starting. I cant replicate this when switching from RUN or ACC to off and back simulating the Start-Run sequence. If I put it from Off-Run it works great it only starts acting up from the run-start-run sequence. I have built a 67 SWB, 67 LWB 4wd, 72 Jimmy and a 72 blazer- same wiring harnesses and wired the same way with no problem. My 3rd gen dodge has a nice pioneer in it and it shuts off while cranking but comes right back on like every other vehicle I have had an aftermarket stereo in.
Click to expand...

Don't care about the sniper or other vehicles - just trying to help with your issue.

Issue: Head unit shuts off after starting vehicle.
Issue: Amps shut off after starting vehicle.

Correct?

If I'm reading the above correctly:
Key in ACC: Stereo works
Key in RUN: Stereo works.
Key from Run-Start-Run: Stereo doesn't work.

Correct?
 
rockota said:
Don't care about the sniper or other vehicles - just trying to help with your issue.

Issue: Head unit shuts off after starting vehicle.
Issue: Amps shut off after starting vehicle.

Correct?

If I'm reading the above correctly:
Key in ACC: Stereo works
Key in RUN: Stereo works.
Key from Run-Start-Run: Stereo doesn't work.

Correct?
Click to expand...

That is correct. The amps and everything work as they should BEFORE trying to start. Once started it will not turn back on by itself or by sitting there pressing the power button, it is completely unresponsive until you turn the motor off and back to ACC or RUN
 
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