Technical Strange headlights

[Tom Atkinson]

We've got a 2004 Fiat based motorhome and mot is due at the end of the month. Checking lights over and dipped beam won't work. If I turn them on first and then turn ignition on they come on but won't come on if ignition is on first . Any ideas please?

 

[Anthony489]

Hi

I attach an elearn diagram for the dipped headlights on the X244 model. This I have marked up in yellow. Please note that elearn is not infallible, so treat it as a guide.

The dipped headlamps are both driven by a single relay. The coil of this relay is driven by the H090 switch control panel "black box" which sits in the centre of the dash behind the switches. It gets commands from the ignition and lighting switches, and is an early version of the more comprehensive Body Control Module used from 2006 onwards. Note that it is designed to extinguish the dipped headlights if the foglights are in use, so check that first ! From your description it would seem likely that the headlights, headlight wiring, fuses and relay are OK. The fault is likely to be within H090.

As this is an electronic unit, no data is published on its internals. What is known is that if this unit does not have all its connectors fitted and all its voltage supplies present and correct it can behave strangely. I'd therefore check that you don't have a fuse blown somewhere on a seemingly unrelated circuit which is preventing H090 from getting the supplies it expects. I'm sure you know that there are fuse boxes both under the bonnet and under the dashboard (plus a scattering of larger ones which would show obvious symptoms if they blew).

This earlier thread may also be of interest: https://www.fiatforum.com/threads/headlights-problem-not-yer-normal-problem.488368/

If you do end up needing a new H090, bear in mind that these are getting hard to find even secondhand.

 

[Communicator]

I cannot add much to the excellent post from @Anthony489 above, other thah to add that while it does not appear on eLearn diagram E2011, Fuse F24 is essential for dipped beam operation. It seems that there are two fuses designated F24. The fuse in question is that in the LH cab fusebox. Upper row fifth from left tan coloured 5A rating. However ii is my understanding that if F24 was faulty, the dipped beams would remain off.

Like wise F37 lower sixtth from left is essential for main beams,

Attached is my wiring connection chart for H090.

 

[Tom Atkinson]

I had the centre dash out earlier this week to replace the heater fan switch.
Just removed it again to make sure I'd not disturbed anything and can't see anything.
I'm sure lights were working before this through.

 

[Communicator]

Some thoughts.

Is the battery in good condition? (When you switch the main beams on, is their brightness OK?) I am just wondering if turning on the ignition causes a drop in the voltage applied to the Switch Control Unit and perhaps the relay for the dipped beams. Also, is the main chassis earth point on the RH inner wing below the battery, in good condition?

 

[Tom Atkinson]

Some thoughts.

Is the battery in good condition? (When you switch the main beams on, is their brightness OK?) I am just wondering if turning on the ignition causes a drop in the voltage applied to the Switch Control Unit and perhaps the relay for the dipped beams. Also, is the main chassis earth point on the RH inner wing below the battery, in good condition?

New battery but not checked the earth point. Will check tomorrow and also check the fuses you mentioned.
Thanks for your help. Mot on Tuesday so could do without this.
Do you think replacing heater fan switch could have anything to do with it?

 

[Communicator]

I cannot see that changing the heater fan switch itself would cause this problem. However did you disconnect and remove the Switch Control Panel to gain access, or could you have inadvertantly disturbed the connectors?

 

[Tom Atkinson]

I cannot see that changing the heater fan switch itself would cause this problem. However did you disconnect and remove the Switch Control Panel to gain access, or could you have inadvertantly disturbed the connectors?

Is the switch control panel where hazard light switch is? If so didn't disconnect it and coul have possibly disturbed something.
Something else to check tomorrow.

 

[Communicator]

Short answer is yes. There is obviously much more behind the switches, It functions as the direction indicator/hazard flasher.

 

[Tom Atkinson]

Checked all fuses this morning and all ok.
Earth wire is good.
Switch control panel is plugged in correctly.
I'm stumped. No dipped beam at all now.

 

[rayc]

Checked all fuses this morning and all ok.
Earth wire is good.
Switch control panel is plugged in correctly.
I'm stumped. No dipped beam at all now.

Time to get a meter out and check for correct voltages, including negatives, as per Anthony's diagram. Are the relays being operated correctly including when ignition is turned on? Does the switch panel pass the negative through? If you do not feel confident then it would be bread and butter for a competent auto electrician.

 

[Communicator]

Checked all fuses this morning and all ok.
Earth wire is good.
Switch control panel is plugged in correctly.
I'm stumped. No dipped beam at all now.

Hi Tom,

@rayc posted while I was writing this. While methods may differ, we seem to be in agreement.

As @Anthony489 has suggested it seems that the problem may be due to a fault in the Switch Control Panel. Have you checked that the direction indicators and hazard lights function are OK?

Before taking more drastic measures it may be worth proving that the problem does lie in switch control panel. This could be done by checking with a small 12V test lamp, as supplied in some fuse kits. (Due to its high sensitivity, a multimeter can give seemingly reasonable results via a high resistance connection.)
A second stage approach would be after disconnecting the battery negative to remove all connectors from the Switch Control Panel, link A8 to D17 on the harness side. Reconnect battery, and dippedbeams should work. With battery disconnected again, remove temporary short, and replace connectors.

If your vehicle is not fitted with foglamps, you may be able to make a more permanent patch between A8 and D17, but to avoid creating further problems this should entail the cutting of the grey wire leading to D17. Leave sufficient length of wire for possible future reconnection.

Test all at least all obligatory lights after working on Panel.

 

[Tom Atkinson]

Thanks for all your help but I'm not confident enough or knowledgeable enough to dig any deeper.
Anyone know of a good auto electrician near Blackpool who's free this weekend?

 

[Tom Atkinson]

Anyone know what this is and if it should be plugged in somewhere?

 

[Tom Atkinson]

 

[rayc]

Anyone know what this is and if it should be plugged in somewhere?

I had a similar connector some years ago to connect a CD changer to my radio

 

[Tom Atkinson]

I had a similar connector some years ago to connect a CD changer to my radio

Thought it was a spare to do with radio.
Clutching at straws.

 

[Communicator]

Thanks for all your help but I'm not confident enough or knowledgeable enough to dig any deeper.
Anyone know of a good auto electrician near Blackpool who's free this weekend?

Please post the final outcome on this thread, as it may help others including me.

 

[Tom Atkinson]

Will do.

 

[Tom Atkinson]

"A second stage approach would be after disconnecting the battery negative to remove all connectors from the Switch Control Panel, link A8 to D17 on the harness side. Reconnect battery, and dippedbeams should work. With battery disconnected again, remove temporary short, and replace connectors."

Tried this today and lights still not working. I'm determined to find the fault.