headlights (main beam)

[fredsajs]

Any thoughts on fuses blowing every time switch to main beam ?.
My donner is a combination of Cortina Mk 3 & 4.
It started with nearside side lamp fuse blown. I traced fault to earth problem and remade earth and cleaned out semi corroded stop/tail lamp holder, fitting new bulb and fuse.
Next day whilst driving noticed main beam warning illumination slightly comimg on/off whilst on side lamps.
Switched on main shell lamps to dipp beam and main warning lamp got brighter.
Assumed switched to main in place of dipp, so stalk switched to dipp. warning lamp went out. But main lamps angle not changed ?, so must have ben on dipp all time.
Switched again to main and lights diddnt change, but main beam warning lamp came on.
Next day found main beam fuse blown. Replaced it ,tryed lights to main beam !, fuse blown again.
Since then and 8 fuses later combinnation of things, headlamps removed from circuit, side lamps removed, all earth to lamp cases tested, all wires to lamps tested for short, all fuse position checked for shorts,Colume switches removed and tryed for shorts and opporation. Every time same main been fuse blows.
Manual says a headlamp relay in circuit. but not original builder and unable to locate it. Found and identified relays I did find. But no main beam relay.
Help...

[andyf]

Re: headlights (main beam)

Check the resistance from the output terminal of the fuse to earth. It may not be a dead short it could be leaking just enough current to blow the fuse.

[Dane_Rescueman]

Re: headlights (main beam)

The headlight system on the Cortina Mk III & Mk IV is a nightmare. Ford used switched earths in some instances and switched live in others. For instance, if the main beam warning light bulb has blown, the main beam relay won't work. This took me a while to work out ! The lighting was operated by a chunky metal relay box containing two relays; both interconnected to react to a switched earth for the change from dipped to main. it also contains the main beam and dipped beam fuses. If your car has been rewired to remove this box then the front lights would need rewiring to avoid the stray switched earths from the Cortina column switch. You can check the big plug on the bottom of the relay box for shorts and corrosion, and the old grey connectors on the engine firewall if you still have them. The Relay box takes its power on a substantial red wire which is swaged in to the main lead from alternator to battery. I found this completely rotten in my car and had to replace the lot. You can make sure that the lights are wired correctly. I found one of mine that had the feed to the bulb case and earth to the bulb centre contactor! This upset the relay box too.
It all boils down to starting from the column switch (I have been through 3 now) and tracing each cable to check correct polarity and for mechanical damage,chafing and rot.
Good luck with it - you will get there in the end.

[fredsajs]

Re: headlights (main beam)

Whot JOY !
18 hrs over 4 days and found fault by pure chance.
Got my head around eventualy that, if I had seperate dipped beam main beam and sidelight left and right all seperatly fused . Then looking for relay that proberble was never fitted,was a time wasting.
So rechecked again and realised a simple mistake. I had been checking for continuety with-out power on cables and shorts to earth. But not checking shorts between cables !.
Found total short within one head light assembly of all wires, but they all looked fine?. Tracing under car found joint of all five head-lamp cables badly water corroded. On pulling appart found unable to free cables from head-lamp shroud via st/st flex conduit.
Removed headlamp and conduit and on stripping found all cables within headlamp conduit were melted together and had water staining all over them.
On checking other headlamp cable conduit found it full of water held in place by cable joint and pvc tape over zelious wrapping.
So morral is .
If you have st/st flex conduit supplied 1986/90 wich is not inner shieved, then it is not waterproof, check and change, esspecially if at base a water dripp hole size is not available to drain away.
Thanks all for helpful idea`s.

[andyf]

Re: headlights (main beam)

Well at least you found it, sometimes it just takes a bit of luck!