Headlights not working MKV Prelude

km666 · Post by **km666** » Tue May 28, 2019 4:41 pm

Seems the issue wasnt the nasty aftermarket headlights. I found a replacement OE set and this is what happens.

Dipped beam = Drivers side - Dipped beam bulb ON, half brightness. Gives 12v earthed to body
- Full beam bulb ON, half brightness, Shows 0 volts
Passenger side - Dipped beam bulb ON, full brightness, Gives 12v earthed to body
- Full beam bulb ON, half brightness. Gives 12v earthed to body
Full beam = Drivers side - Dipped beam bulb OFF, Shows 0 volts
- Full beam bulb OFF, Shows 0 volts
Passenger side - Dipped beam on, full brightness, Gives 12v earthed to body
- Full beam on, full brightness. Gives 12v earthed to body

All bulbs and holders in headlights have continuity. Wierdly as do all the connections that plug into the back of the headlights, each of the 4 connections show continuity across pins and continuity from power pin to earthing bolt on the wing for either side.

What am I looking at with all this? Is it wiring or relay issues? Its as though both of the bulbs in the passenger side are acting as high beam, which is why drivers side is turning off completely, with low beam spread across all 4 main bulbs although passenger side low beam is at full level brightness. Yet the two are seperate sections of loom, they dont bridge under the bumper support like they do on other cars. The driver side loom seems to do drivers side headlight, driver side fan switch and both horns, it also has one unused honda type connector set low and one unused single round pin conenctor similar to a HT lead. Passenger does passenger headlight and passenger side fan switch, AC motor and has mirrored one unused honda type connector set low.

Post by **newkid** » Wed May 29, 2019 11:20 pm

Anything like the 4th gen it will be

https://www.ebay.co.uk/p/H4-X-2-Bulb-Ho ... FwQAvD_BwE

Obviously get correct fitment for 5th gen.

They dry out an go green inside giving a poor connection.

km666 · Post by **km666** » Thu May 30, 2019 12:13 pm

I'll have to give them a try, they seem packed with some kinda of grease.

Post by **newkid** » Thu May 30, 2019 3:47 pm

Chances are it's melted on the inside giving a bad earth. Could be stalk but your getting 12v.

Only other thing is to check all fuses. Sure the headlights have a fuse per side in the engine bay fuse box.

YouTube · Post by **Sailor** » Thu May 30, 2019 9:38 pm

I'm with @Newkid, in that it does sound like an earth thing. The relay(s) seem to be operating, so it must be wiring or earths?

km666 · Post by **km666** » Sat Jun 01, 2019 5:22 pm

I ordered a relay along with the new wiring. I had checked the fuses before and swapped the L and R headlight fuses around but the issue remained on the drivers side so didnt think it was a fuse issue. However when I plugged the 'new' relay in the headlight fuse popped straight away and by swapping the L and R fuses could shift the issue to the other light if that makes sense.

I can hear the 'new' relay clicking when dipped are turned on and again switching to full beam, where the old one didnt make any noise. Seems very odd to me but they're now both working and switching between high and low.

The bulb holders were pretty manky and looked as though they'd reacted with something, they were covered in a black sticky paste as well as the insides being packed full of a tan coloured grease so I replaced those anyway since they were only a few quid for the set.

I know with my BMW on canbus it'll detect a bulb is out and illuminate a different bulb to compensate but obviously the Prelude isnt on canbus.