327IROC85

Hello folks,
First post on this forum but I have been a lurker. Lots of great help on the forum and I am hoping someone may have knowledge to my questions.

The ride is a 1985 IROC Z28.
I am probably the 4th or 5th owner of the vehicle and the wiring in this vehicle is a nightmare.

Situation:
When I pull the headlamp switch all the way out, I get lights on all four headlamp with the inner lights, high-beams just a touch dimmer.
When I toggle the high-beam switch the outer lights, low-beams will remain on and appear to be a touch dimmer while the inner lights, high-beams are now brighter.

Question:
What module or relay circuit regulates the voltage to this?

Why?:
I am installing a light harness and most of these relays are off (0V) or on (12V). So as you can imagine I either get lights or NO lights (dangerous!!!) if I toggle the high-beam switch and need to push in the headlamp switch for full off and pull back out to lights again.

Voltages as measured (battery was a bit low):
Regular driving mode Low-beam plug, Low filament wire = ~10.35V
Regular driving mode Low-beam plug, High filament wire = ~9.33V
Regular driving mode High-beam plug, filament wire = ~9.33V

High-beam driving mode Low-beam plug, Low filament wire = ~0V
High-beam driving mode Low-beam plug, High filament wire = ~9V
High-Beam driving mode High-beam plug, filament wire = ~11.05V

I either need to find a relay that can toggle based on voltage changes or find what is controlling this in the vehicle to disable it.

Side question:
I understand the side markers share a ground or rather pulse on and off - what is the best way to 'splice' in a ground because my driver side does not work now that I 'fiddled' with headlamps =(

Sorry for the long post but I rather be detailed with the ask request.
Thanks in advance for anyone/everyone's time!

deadbird

This is for 86, all years the same...

327IROC85

Hi deadbird,
Thank you for the schematic.

Do you know what the "F1" to "A2" is? Is that the bridge that provides some power to the high-beam circuit?

I do not clear see on the diagram how the high-beam and low-beam circuit receives partial voltage power?

MoJoe

iTrader: (5)

F1 and A2 are in the C100 connector, which is the big one through the firewall, closest to the driver side fender.

The only thing that will drop resistance in this circuit is the wiring itself... Hence, the market for a relay switched harness power straight from the battery, where the factory wires just control the relays.

If the highbeams are on in both switch positions, either you have a bad switch or a short in the wiring, connecting the low beam to the high beam circuit. Another answer could be a bad ground... voltage on the low beam circuit goes through the low beam filament to the ground wire, with nowhere to go but back through the high beam filament to find another ground.

ETA: Note there are two grounds: G103 & G104, one for each side. Make sure both of those grounds are clean and secure.

327IROC85

Thank you for the response.

Please note, the high-beam is not on full bright during normal operation with the low-beam, only partial brightness.

When I toggle to high-beam operation, it comes on full bright.

Help me understand something. If I were measuring voltage on the wires during regular driving mode, what would be the expected values?

Would it be:
Regular driving mode Low-beam plug, Low filament wire = ON ~12V
Regular driving mode Low-beam plug, High filament wire = OFF 0V
Regular driving mode High-beam plug, filament wire = OFF 0V

If you have this manual, what is on page 100-5?
I am curious to know what C100 and C102 are.

Are the G103 and G104 the ground wires coming off the headlamp plug ground wire to the light-housing then to the chassis?

MoJoe

iTrader: (5)

10V-12V when on. The drop is due to wire resistance.

G103 & G104 run from the hi & low plugs to chassis ground. Each side is separate.

327IROC85

Turns out I had "dirt" preventing the nut on the chassis ground of the driver lights to connect well. Once I clean it up, the side markers were working as expected however my headlamp issues still remain. I believe I will need to pull the dash to investigate the switch.

Thank you everyone for the feedback - I am on track =)

MoJoe

iTrader: (5)

Glad you found the ground issue. The headlight switch provides power to the hi/lo switch which is on the steering column. Since you don't have a problem with the basic on/off portion, but the hi vs lo, look to the steering column.

Remove the trim panel. Remove the two nuts holding up the column. It may droop enough for you to get at the switches. Move the turn lever forward/backwards, find the rod that is moving to find the switch.

Pull the plug with three wires... hot, low beam, high beam. Turn on the headlights... which won't because you've interrupted the circuit.
Jumper any two connections:
- low to high will get you nothing
- hot to low should give you just low beams
- hot to high should give you just high beams.

Before doing all this, do you have fog lights? Check that relay, near the charcoal can and horns. IIRC turning on the high beams cuts out the fogs. Make sure that wiring isn't buggered.

327IROC85

Thank you for the wiring test run down!
No fog lights. That said, I will still search high and low as I am not the first owner and clearly previous owners had "monkeyed" around =(

I have to pull the dash and steering column anyway to figure why the mist/windshield fluid spray is not working. I may just splice in a separate pump as was done factory for newer models as my wiper pump motor is extremely close to the motor after the swap.

Thanks again for all the information!