No low beam headlights.How to use HOA mod to fix?? '03 Avy

So I hopped in the truck the other night and I had no headlights. You need headlights between 4:30pm to 8:00am and its fresking cold..Anyway.. I did a little research and came across people saying they solved similar issue with the High-on-All mod.. I tried connecting the low beams to the highbeams just fine..but the low beams will not come on without the highbeams. The relay works and fuses look fine. Any help would be greatly appriciated.
I dont care if I get AOH but I need my low beams?

JVZL1 said:

The first I wold check would be the diodes. They are directional you can check with a meter you would also eliminate the diodes. I'm sure more will come. 

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He posted the low beams only come on with the high beams so the diodes are good.



Sounds like a switch to me.

Have you tried swapping the relays

Yes I did try swapping the relays. Relays are working.....So the fact that the lowbeams turn on with the highbeams(with the mod) but not Automaticallyor when switched to low beams. Would that be a indication of a broken/bad ground wire?

RabidLab said:

Yes I did try swapping the relays. Relays are working.....So the fact that the lowbeams turn on with the highbeams(with the mod) but not Automaticallyor when switched to low beams. Would that be a indication of a broken/bad ground wire?

Click to expand...

That is one possibility.  Some basic electrical troubleshooting is required here.  Since you have an 03 the relay switches the ground side - you should always have + voltage at the bulbs' sockets when the truck is running.

I gambled and replaced the switch...It is not the switch. Relays are good, both low beams will come on when the diode is ran from High beam relay to low beam relay Pin 85 to 85.... looking for a 9v battery for my multimeter.

enoniam said:

That is one possibility.  Some basic electrical troubleshooting is required here.  Since you have an 03 the relay switches the ground side - you should always have + voltage at the bulbs' sockets when the truck is running.

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Probably wouldn't worry about diodes & the pins' 85.  Follow this man's advice & go where the evidence leads.

On an '03, there could be a broken wire almost anywhere in the harness. 

Something else to consider:

Tilt steering wheels have been known to take its toll on wiring, over time.  Double-check the condition of the associated wiring & connectors that feed the multi-function switch.

Since you have done the "all on" mod you may want to inspect the socket that the relay goes into. This is the sort of issue that can happen when pushing the diode into the socket along with the relay.

You should be feeding +12 volt to two of the pins in the relay socket and one should be ground when the lights are turned on.
Be careful when testing the pins in the socket and only use a digital VOM otherwise you can damage the BCM.

You MAY get a ground on the pin going back to the light but likely won't.

If you are getting the correct voltages at the relay socket then the installation of pins into the sockets has likely damaged them and you will need to try bending the pins in a manner that allows them to contact the relay properly.

This is why when I did this mod I soldered wires to the bottom of the relays and did NOT insert anything into the socket its self.

MS03 2500  has mentioned a circuit board that someone made that does this mod for you too and looked like it doesn't cause this pin damage.

If you check and your not getting the voltages then I would strongly suggest disconnecting your battery and pulling up the under hood fuse panel and check for rodent damage.

The rodent issue gets worse, on the later models.

Some of the relays on the '03 become non-seviceable on the GMT-900's.  Maybe, sooner.

Here's a list of non-serviceable PCB (printed circuit board) GMT-900 relays that could cause problems, even though the associated wiring & fuses are intact:

Underhood Fuse Block, Re-Considered

When you think about it, the fuse block is a multi-layered printed circuit board.  Some components are soldered-in. Some, are "serviceable."

So, all a rodent has to do is use the fuse block as a warm place to go to the bathroom.  Wires, underneath, can still be good.

Non serviceable relays is a very stupid idea.
Relays eventually go bad due to arcing of the circuit within the relay causing the contacts to weld together. Unless using a solid state switch that doesn't have this issue it makes it an expensive repair for what is a $2 part normally...

Rodney