C4 Headlight Ground Location
08-30-2014, 01:31 AM
#1
Drifting
Thread Starter
C4 Headlight Ground Location
I am having problems with my headlights being dim on my 1990 C4. I measured the voltage between the black wire (ground) and the tan wire (low beam positive) on the headlights, and found the voltage is 11.5v, lower than it should be. I've come to the conclusion that either a contact is bad in the headlight or there is a bad ground connection. My problem lies in the fact that there are tons of grounds, and I'm not sure which one is for the headlights. Does anyone know?
08-30-2014, 06:13 PM
#2
I am having problems with my headlights being dim on my 1990 C4. I measured the voltage between the black wire (ground) and the tan wire (low beam positive) on the headlights, and found the voltage is 11.5v, lower than it should be. I've come to the conclusion that either a contact is bad in the headlight or there is a bad ground connection. My problem lies in the fact that there are tons of grounds, and I'm not sure which one is for the headlights. Does anyone know?
The 11.5 at the lamp isn't surprising. Use a jumper and put the alternator out-put voltage to the headlamp and see what the lamp does. If that makes a dramatic difference consider using the alternator voltage through relays to power the headlamps. It should make an impressive difference. What does your alternator show as out-put voltage?
You checked both sides? Check also @ high beam terminal.
The grounds are left side @ the frame near the park/turn lamp and the right side is the same location on the right.
Last edited by WVZR-1; 08-30-2014 at 06:21 PM.
08-30-2014, 06:32 PM
#3
Drifting
Thread Starter
You measured that with just lamps on or with key-on/engine off OR engine running at idle? Pick up the RPMs and measure or start and measure voltage again @ 2000RPM maybe. I doubt it's a lamp issue but maybe a charging system issue. Could it be? certainly.
The 11.5 at the lamp isn't surprising. Use a jumper and put the alternator out-put voltage to the headlamp and see what the lamp does. If that makes a dramatic difference consider using the alternator voltage through relays to power the headlamps. It should make an impressive difference. What does your alternator show as out-put voltage?
You checked both sides? Check also @ high beam terminal.
The grounds are left side @ the frame near the park/turn lamp and the right side is the same location on the right.
The 11.5 at the lamp isn't surprising. Use a jumper and put the alternator out-put voltage to the headlamp and see what the lamp does. If that makes a dramatic difference consider using the alternator voltage through relays to power the headlamps. It should make an impressive difference. What does your alternator show as out-put voltage?
You checked both sides? Check also @ high beam terminal.
The grounds are left side @ the frame near the park/turn lamp and the right side is the same location on the right.
The alternator voltage gauge is always good when I drive (not sure the exact volts, but probably 2/3 of the way to max).
It was getting late, so I didn't check high beam voltage too, but I will next time I have a minute to do so.
08-30-2014, 06:42 PM
#4
I measured it with key on engine off. The battery voltage read about 12.5v at the time.
The alternator voltage gauge is always good when I drive (not sure the exact volts, but probably 2/3 of the way to max).
It was getting late, so I didn't check high beam voltage too, but I will next time I have a minute to do so.
The alternator voltage gauge is always good when I drive (not sure the exact volts, but probably 2/3 of the way to max).
It was getting late, so I didn't check high beam voltage too, but I will next time I have a minute to do so.
08-31-2014, 03:20 AM
#5
Race Director
The grounds for the headlights are on the frame rails next to the horns.
The voltage on the headlights goes through the headlight switch and connector C100 on the firewall.
The voltage on the headlights goes through the headlight switch and connector C100 on the firewall.
09-01-2014, 07:33 PM
#6
Drifting
Thread Starter
Okay, I cleaned one of those grounds already. I'll do the other and see if it helps.
10-07-2014, 11:38 PM
#7
Drifting
Thread Starter
Now that I've gotten it smogged, I finally had time to check the voltages with the engine running.
Driver's side light: 11.05v
Passenger side light: 10.95v
Looking back, I see that previously I measured 11.5v. How would the voltage be less with the engine running?
It was just at idle, but once my dad is able to help me I'll check with it at 2000 RPMs.
If the problem is my lamps, I've heard that Hella makes a set that seem to be highly regarded for use in the C4?
Driver's side light: 11.05v
Passenger side light: 10.95v
Looking back, I see that previously I measured 11.5v. How would the voltage be less with the engine running?
It was just at idle, but once my dad is able to help me I'll check with it at 2000 RPMs.
If the problem is my lamps, I've heard that Hella makes a set that seem to be highly regarded for use in the C4?