Where to start?

[Locknut]

Hi guys, a bit of a strange one... hoping there might be some blokes that can point me in the right direction

When the car headlights (factory) are turned on the rear floodlights (aftermarket) turn off. A few points to note:
- rear floodlights are not connected to an activation wire, only a relay with an in cab switch
- rear lights are connected to the aux battery and earthed via the chassis
- this issue only happens within the first few minutes of the car being started, however both aux and main battery never drop below 13v (except for the initial start), so all relays should work normally

I’m not sure if the issue is related to the headlights or that there is simply a load on the car when the headlights are turned on. As the rear floodlights are not connected to any reversing lights (factory) or fuse taps I don’t think it’s a negative activating relay issue. I’ve tried activating other circuits which are all powered via the same aux battery bus then turning on the headlights but they operate normally.

Any ideas on where to start would be greatly appreciated.

[flip9]

When it starts working again after the first few minutes, does it coincide with the dual battery system starting to charge the aux battery?

As a test try connecting the negative of the flood light directly to the aux battery rather than to chassis.

[Locknut]

No to your first question, I have a voltage and amp gauge inside the truck. It seems to coincide with when the aux battery is fully charged, I’m only talking about a very small overnight discharge. My battery charger will take around 10 seconds to start charging the aux battery then about another 2-5 mins to top up the battery.

I’ll connect up the ground directly to the aux battery and report back

[flip9]

Ok. Grab a multimeter and measure the voltage between pin 85 & 86 (relay coil) and then measure Pin 87 to Ground.

This will let you know if the relay coil is being energized or no power is being fed to the lights.

Try another relay too since it only takes 2 seconds to swap.

[Locknut]

Sorry for the delay, had a back injury so I was immobilised for a few days. Here goes:
85-86 12.3v with the high beams off
85-86 0v with the high beams on
87-GND 12.3v with the high beams off
87-GND 0v with the high beams on
Tried another relay and switch but no luck
Also ran a direct line between the return ground and aux ground

Any ideas? This stuff really makes my head hurt!

[flip9]

Sorry for the delay, had a back injury so I was immobilised for a few days. Here goes:
85-86 12.3v with the high beams off
85-86 0v with the high beams on

Any ideas? This stuff really makes my head hurt!

Okay so the relay coil is losing power. Do you know where the in cab switch is connected to?

To me it sounds like you have it connected to the headlight circuit? This will act like 12v when the headlights are off but will turn to GND when high beam is selected.

[Locknut]

I think you’re spot on now that I think about. I reckon I’ve piggybacked an earth tap from the spot lights! Thanks a million! I’ll verify this tomorrow

[Locknut]

Thanks for taking the time to answer my question flip9, you were spot on

[flip9]

All good mate. Just find a constant 12v power source and she'll be alright