[RBwonga]

Afternoon all,

Sorry for the probably basic question, I'm new to Suzuki's and to electrics.

Both my low beams turned off the other day when driving, high beams work still. I assumed dead globes. I have changed both globes and checked with a new combo switch, still no low beam. But I have figured out if I put a wire to the back of the low beam terminal and ground it, the light will come on. I also tried moving the factory earth from the little flat bar and still nothing.


Any help would be awesome!

[bumstein]

Gudday

Not sure this will be much help and it’s obviously difficult to know what’s causing a problem without being able to see the car first hand.

My first bet would have been on the combo switch but you say you’ve checked with another and that didn’t solve the problem? Just to check, have you plugged in a different combo switch and make sure it’s grounded properly before testing it?

When you tested an alternative combination switch did the high beams and any other functions (park lights, indicators etc) work?

Ground is the likely the cause but it can be a little difficult to chase down exactly where. Sierra’s are negatively switched which means:

-There is always 12v power to the headlights
-when you turn the headlights on you complete the circuit to ground
- when you turn them off it opens the circuit on the ground end

Most circuits work the other way, ie the switch completes the circuit on the positive side and allows the power to then flow through the headlights.

That might be confusing but it means your problem is downstream of the headlights. You grounded the low beam terminal (red wire with white tracer I think?) which bypassed the the whole switch assembly. That means there is power to the headlight and the globes work.

Have a quick look at the connectors near the headlights, ( it’s a round connector) and make sure they’re not corroded or broken.

If you’re sure the combination switch is definitely not the problem then it’s time to get a test light or multimeter and work your way from the headlight connectors down the line seeing where your voltage stops.

If you’ve got a multimeter I’d be doing it this way.

Disconnect the battery and hook your multimeter ground to the negative terminal on the wiring (not on the battery you’ve just disconnected.

Turn the multimeter to continuity with the beep function if it has one.

Turn the headlights switch on (remember you’ve disconnected the battery so there will be no voltage in the system.

Work your way from one end to the other. touch the positive wire of the multimeter to the headlight terminal that you grounded. I’m going to assume that there is no continuity between there and the negative battery terminal.

If it DOES NOT have continuity then the problem is further downstream.

Follow the wiring downstream from there towards the combination switch testing each part being the connectors in the wiring harness. When the beep finally goes off you know the problem is between there and the last spot you tested without a beep.

You’re following the red wire with white tracer (double check that, I’m going off memory). Not sure if that makes it clearer or more murky, but hope it helps somewhat

[MrRocky]

I had a similar issue, turned out the large earth wire under the glovebox (on the round crossbrace/dash support) had been getting a drip of water and had corroded.
Cleaned it up hey presto lights back. It did take me a couple weeks to figure that one out.

[HarryHoudini]

Common problem on Sierra's as they age, options have been detailed in the above Posts,you just have to put the time in to find the fault which is often a break in the wiring itself if its not earth/grounding problems due to corrosion.
At a $100+ ph its not really an option to seek help from an Auto Electrician,its easier and cheaper to run additional wires and/or replace switches.

Edit..my brother reminded me a local guy had exactly the same problem,swapped high beam connector to the low beam somehow and just left it at that,no high beam.

[RBwonga]

bumstein wrote:

Gudday

Not sure this will be much help and it’s obviously difficult to know what’s causing a problem without being able to see the car first hand.

My first bet would have been on the combo switch but you say you’ve checked with another and that didn’t solve the problem? Just to check, have you plugged in a different combo switch and make sure it’s grounded properly before testing it?

When you tested an alternative combination switch did the high beams and any other functions (park lights, indicators etc) work?

Ground is the likely the cause but it can be a little difficult to chase down exactly where. Sierra’s are negatively switched which means:

-There is always 12v power to the headlights
-when you turn the headlights on you complete the circuit to ground
- when you turn them off it opens the circuit on the ground end

Most circuits work the other way, ie the switch completes the circuit on the positive side and allows the power to then flow through the headlights.

That might be confusing but it means your problem is downstream of the headlights. You grounded the low beam terminal (red wire with white tracer I think?) which bypassed the the whole switch assembly. That means there is power to the headlight and the globes work.

Have a quick look at the connectors near the headlights, ( it’s a round connector) and make sure they’re not corroded or broken.

If you’re sure the combination switch is definitely not the problem then it’s time to get a test light or multimeter and work your way from the headlight connectors down the line seeing where your voltage stops.

If you’ve got a multimeter I’d be doing it this way.

Disconnect the battery and hook your multimeter ground to the negative terminal on the wiring (not on the battery you’ve just disconnected.

Turn the multimeter to continuity with the beep function if it has one.

Turn the headlights switch on (remember you’ve disconnected the battery so there will be no voltage in the system.

Work your way from one end to the other. touch the positive wire of the multimeter to the headlight terminal that you grounded. I’m going to assume that there is no continuity between there and the negative battery terminal.

If it DOES NOT have continuity then the problem is further downstream.

Follow the wiring downstream from there towards the combination switch testing each part being the connectors in the wiring harness. When the beep finally goes off you know the problem is between there and the last spot you tested without a beep.

You’re following the red wire with white tracer (double check that, I’m going off memory). Not sure if that makes it clearer or more murky, but hope it helps somewhat

You're a legend mate! Found the corroded plug underneath the dash on the passenger side. Have just bypassed the plug for now. Happy days!