Chevy High Performance
Click here to find out more!

Electric system going crazy

  
Chevy High Performance
Item Posts    Sort Order

Electric system going crazy

 
leejustin2369 leejustin2369
New User | Posts: 7 | Joined: 12/13
Posted: 12/08/13
09:26 PM

Hello guys I have a 1979 Silverado 1/2 ton 350. I tried jump starting my truck and placed the jumpers on opposite terminals, in doing so i seen smoke coming from the engine bay and it ended up burning through one of the wires coming from the junction block. I replaced the wire and then all my trouble started. My truck will start and run just fine.. But heres the problem all of my electronics go haywire. For example when i turn the headlights on the drivers side is very dim and when i turn the steering wheel it goes back to normal brightness and when i turn on the heater blower the passenger turn signal turns on and lights dim and all of the gauges go crazy. Wipers only are very slow. The only way that everything works properly is if I'm not driving the truck and the heater is on full blast with headlights on and the steering wheel is in a certain position. I have torn the dash apart and looked for any signs of whats wrong.. I am pretty decent with electronics and the understanding of them so I've done some troubleshooting but now I am completely lost and any ideas will help.. Thanks in advance  

dond1965 dond1965
Enthusiast | Posts: 294 | Joined: 12/13
Posted: 12/08/13
09:56 PM

start with the turn signal switch and its ancillary wiring, ol wayne can get you a lot further than myself with wiring.... good luck bro!  

wayne712222 wayne712222
User | Posts: 197 | Joined: 10/13
Posted: 12/08/13
11:44 PM

please perform the second half of this test..


then post results.. by number...

1...
2...
3...
4...

this really does work...

this should be printable..

~~~~~~~~~~~~~~~~~~~

Voltagedroptesting


~~~~~~~~~~~~~~~~~~~~~~~  

wayne712222 wayne712222
User | Posts: 197 | Joined: 10/13
Posted: 12/09/13
12:00 AM

please. make sure that you have a braided ground strap from the back of the engine to the firewall.. and that its connected to the good locations that are clean..

Ground Strap 15 Inch Zpsbc9293c1

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


you will need to print this one also.. or slide it to the right..

please continue the voltage drop test... between the positive battery post and the terminal block shown at right..its actually on your firewall just to the passenger side of your distributor...  i have found so many of those with burned connections and you could also have a partially melted fusible link there.

77 80 Chevytruck Fusible Links  

wayne712222 wayne712222
User | Posts: 197 | Joined: 10/13
Posted: 12/09/13
12:08 AM

80S Chevy Truck Battery Cables  

leejustin2369 leejustin2369
New User | Posts: 7 | Joined: 12/13
Posted: 12/09/13
04:48 AM

I just got to work for the day i will try this when i get home.. So you think that my problem is some voltage is being lost some where due to a bad ground? Ive checked most of my grounds that i could see but i didn't check the one from the back of the head to the firewall i will make sure to run the test and then check that.  

leejustin2369 leejustin2369
New User | Posts: 7 | Joined: 12/13
Posted: 12/09/13
10:30 AM

Also on the voltage drop test it says to turn the headlights on.. In my post i said that the only way the headlights work is if i turn the steering wheel in a certain position. Should i turn the steering wheel where the lights are on or off for the voltage drop test?  

leejustin2369 leejustin2369
New User | Posts: 7 | Joined: 12/13
Posted: 12/09/13
10:31 AM

Also on the voltage drop test it says to turn the headlights on.. In my post i said that the only way the headlights work is if i turn the steering wheel in a certain position. Should i turn the steering wheel where the lights are on or off for the voltage drop test?  

leejustin2369 leejustin2369
New User | Posts: 7 | Joined: 12/13
Posted: 12/09/13
07:29 PM

Okay so when i got home first thing i checked was for that ground strap from the head to the firewall.. Couldn't gind any such thing so as a method of checking grounds i took a pair of jumper cables and put one of the black leads on the negative terminal of the battery and the other black lead to a bolt on the firewall i then took on of the red leads and placed it on the alternator mount and the other red to another bolt on the firewall. Turned my headlights on and instantly brighter. Even if i turn the steering wheel the headlights stay on along with the heater (unlike before where they both turned off) so from there i wired up a ground from the negative battery terminal to the firewall. Used thick gauge wire to do so but now i have a new problem. When my lights are on the flashers are on but not flashing just a steady solid light but when i turn the left turn signal on the left starts to flash on the outside BUT the indicator on my dash shows that the right flasher is going off. So i ran the voltage drop test and got this

1. 10 volts
2. 0 volts
3. 0 volts
4. 0 volts
I know that you said 0 was an invalid answer but no matter where i tried thats what i got..  

dond1965 dond1965
Enthusiast | Posts: 294 | Joined: 12/13
Posted: 12/09/13
08:19 PM

sir you MUST have a ground from the engine block to the body and or frame, it is priority one!! take care of this step first, then see if you still have problems.that turn signal switch still seems suspect, but so does the emergency flasher switch. fix the ground and ol waynes advice shall get you somewhere.  

wayne712222 wayne712222
User | Posts: 197 | Joined: 10/13
Posted: 12/09/13
10:32 PM

One step at a time.. LETS get the main ground wires hooked up first..

without the main grounds hooked up properly.
neg bat to engine block.
neg bat to body
engine to body..
it will be like plugging in an extension cord and a circle saw.. but the wires from your house to the pole have not been installed yet..  must need a new saw.. it does not work..  wrong..

lets fix the grounds.. the braided strap i posted above has a part number on it that should be available at almost any parts store for about 5 bucks..

why the braided . its more flexible.. the wires are finer and there is more of them.. and electrons travel on the surface of the wire.. the electrons can also jump from strand to strand to take the shortest route..



run the test without the jumper cables..

i wonder if your alternator is actually working with 10 volts.. but ..

if its not putting out close to 14 volts.. you will have issues..

got a test light..

engine off.. headlights off..  key off..

test light hooked to the alternator housing or mounting bolt..

probe the wire on the stud on the back of the alternator.. do you have power???

probe the large red wire into the side of the alternator.. do you have power???

the small wire on the side of the alternator is hooked to the light in the dash board.. and the other side of that bulb is hooked to the alternator light if you have one.. you could on a 79 have a volt meter.


say... also.. when you are running the 4 part test.. without the jumper cables.. try it on a WORKING CAR.. just to check it out..  in fact try it on TWO different cars.. chances are that one might need service..

if you get 0.00 volts ON test 2, 3, and 4..  please change the meter setting to 2 volts DC scale..

the drawings above.. with the red wires marked out is a 77 to 80 chevy truck  as is the other image..  with the green and red lettering..  

wayne712222 wayne712222
User | Posts: 197 | Joined: 10/13
Posted: 12/09/13
10:35 PM

battery negative to battery positive.. expected 14.1 to 14.8 volts.

Battery Negative to the engine block  expected 0.04  volts..

Battery negative to the body.. expected 0.02 volts

Engine block to the body.. expected 0.02 volts

these will be off if the alternator is not working..  

dond1965 dond1965
Enthusiast | Posts: 294 | Joined: 12/13
Posted: 12/10/13
06:39 PM

wayne you really do good work bro!  

leejustin2369 leejustin2369
New User | Posts: 7 | Joined: 12/13
Posted: 12/10/13
07:13 PM

So i made all of my grounds good.
negative terminal to alternator mount
Negative terminal to firewall
Firewall to alternator mount

When i did that i re ran the voltage drop test
1. 14.19 volts
2. -.02 volts
3. -.01 volts
4. -.03 volts

My alternator is brand new i replaced it when i fried the original wire on the firewall that started my problem so i don't know if that makes a difference if you're determining if its a bad alternator.

Also another symptom of my lights problem is that when the dims are on it works fine when the brights are on they flash opposite  

wayne712222 wayne712222
User | Posts: 197 | Joined: 10/13
Posted: 12/10/13
09:32 PM

those numbers look great..

14 volts is great.
the rest are fine..



lets look at the front lighting for more ground issues...

i am thinking that you are talking about the headlights being on DIM/LOW.. and brights /HIGH

follow the electrical wiring from the back of the headlights.. i don't recall if its grounded on the inside of the radiator core support or on the outside..  but there are 3 wires on a LOW beam.. light green  and a Tan wire but a third is black.. black is the ground and it needs to be connected to the body..  and the body to the battery negative..

you can also .. engine running.. headlight on.. run a voltage drop test to the ground ring terminal from the headlights..

you might also want to run from the negative to the radiator core support to make sure its not insulated by the paint..

lets do the same thing for the turn signal and parking lights on the front ..

3 wires..   brown is running lights..    light blue or dark blue are the turn signals..  black will be a ground..  again.. these are usually connected to the radiator core support also..

now.. i don't recall which turn signal sockets are used on a 79...

if the front or rear turn signal lights are giving you issues..

Groundtestingbulbs Zps32d937b7



if you are talking about the side marker lights..

on a 79... they will flash out of phase with the turn signals.. because of the cool way they are wired..

prior to .. 76/75.. the side marker lights came on with the parking or tail lights and were connected to ground...

after that time..  they removed the ground side of the connection.. and wired it to the turn signal on that side.  this makes them flash when the turn signals are on..




parking lights on...     brown wire hot..    thru side marker light to turn signal wire.. thru turn signal filament to the ground on the turn signal bulb to make the side marker light glow...

the side marker filament is much smaller than the turn signal filament so it does not glow when this happens..

when you turn on the turn signals on that side.. when there is power in the turn signal circuit.. the side marker lights cannot get any ground thru that short cut so the bulb goes dark.. as there is positive voltage on both sides of the bulb...
so it flashed out of phase with the turn signal lights..

lastly.. when the parking/headlights are NOT on..  when the turn signal circuit is active.. the power goes thru the side marker bulb the other way and gets a ground thru the parking lights filaments.. since there are more than one parking light filament on that circuit.. there is enough current to turn on the side marker lights..


try to describe the issues.. i am taking wild guesses.. hope i am right..