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zob

Fitting relays to headlights

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zob

On @steveo3002's recommendation I had a go at fitting a relay loom to my headlights just now but the idle became funny with the relays wired in so I promptly ripped the lot out.

 

I assume either A) There's something duff about my Chinese ebay loom or B) I wired it in wrong. No instructions so I went with:

3-pin male plug to one of the existing headlight sockets

Both 3-pin female sockets to the lamps

Red wire with the 40A fuse direct to the +ve battery terminal

Both blue wires with the rings on them to the nearest earth points I could find either side.

 

Not a big deal, just a nice-to-have if I can get it right eh.

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steveo3002

sounds correct ...some pics would help incase its made wrong

 

you need to unplug the thing near the fuse box with yellow wires

 

 

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zob
42 minutes ago, steveo3002 said:

you need to unplug the thing near the fuse box with yellow wires

 

Ah. Yes I certainly didn't do that. Thats the dimming resistor isn't it?

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steveo3002

does kinda sound like theyve wired it wrong  

 

wouldnt be hard to bench test if you have a spare bulb and some scraps of wire

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1vw2many

I wanted this mod and steveo gave me a link for the loom and replays . I haven't had time buying one yet . I shall keep my eye on your progress zob.

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zob

Had another look at it and everything appears correctly wired, or at least the wiring matches the diagram in that Daniel Stern link above. popped it back on the car (without routing the wires properly this time) and I could hear the relays tick on and off for low and high beam. However the car's idle is significantly worse with this loom in place, even with the lights off. The idle hunts - and actually it was a little worse than usual still after I removed the relay loom and started it up again.

 

Seeing as I've only -just- got this thing running nicely I'm not quite sure I want to get back on its bad side. Could it be my alternator (or its voltage regulator) is on the edge and drawing some extra amps is a little more than it can handle? Only thing I didn't do was unplug the yellow resistor - its soldered rather than spade connected so didn't want to faff around with it. Its just for the 'daytime running' mode right? With the loom connected there was no difference between main beam and daytime beam which makes sense.

 

All seems very odd.

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steveo3002

should be a plug on that yellow wire unless its been messed with 

 

cant think of a reason why it would spoil the idle ...lighting harness isnt really related to the engine loom 

 

the load should be similar with or without the relay  

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zob

I agree! Well, I'm going to leave this as its not essential and I wasn't particularly unhappy with my lights anyway. I'll revive the thread if I have another crack at it some time and get it working. 'Damp squib'.

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zob

Had a look at te relay wiring and that Daniel Stern page again with my morning coffee at work - the ebay harness has different relays, one of which is a 5-pin with the normally closed (NC) pin wired in to something. Is this the problem I wonder? The battery is directly connected to something while the headlights are off... if it was shorting to earth then that might explain the weird idling? You can see the 5-pin relay on the right.

image.png.2b76bba6de22095368190f761019001d.png

In the wiring diagram below there are two 4-pin relays used, dead simple, one for high-beam and one for low.

 

image.png.a3e8b3f72e64e6ede6619ab3d41842bc.png

I'm in the office so can't interrogate the loom but my gut feeling is that the 87a pin on the second relay is wired to something that is causing a big load which could explain why the performance on main beam with the loom was pretty guff but on full beam (switching away from that 87a terminal on relay 2) they looked alright. The idle is always a bit worse with the lights/demister etc on as the alternator is under increased load. Could it be that this NC terminal is shorting/loading the alternator enough to produce that slighty worse idle too?

 

 

 

 

 

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steveo3002

you would think something shorted to earth would pop a fuse or melt the wire rather quickly

 

sorry its dud ...it should be just like the diagram in the link , can probably adapt it to be correct , relays are cheap 

 

 

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zob

Yeah after writing that I thought better about an earth short - coffee hasn't quite got there yet!

 

Meh, its pretty good for 9 quid to be honest - be hard pressed to buy all the parts for that. I''ll have a go at adapting it to the diagram this weekend I think.

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steveo3002

yeah ive reccomended to several people , im sure you can make it work

 

i wonder if its made to keep low beams on with high beam or something daft ? 

 

couple of better quality relays wont hurt anyway

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nige8021
30 minutes ago, steveo3002 said:

 

i wonder if its made to keep low beams on with high beam or something daft ? 

 

 

That would be the only reason for having that change-over relay, check if both relay coils are wired in parallel ? 

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zob
30 minutes ago, nige8021 said:

 

That would be the only reason for having that change-over relay, check if both relay coils are wired in parallel ? 

 

Aye, will do

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zob

Had a proper look and probe of that loom and it made sense - both relay coils were wired parallel, honestly nothing wrong with the thing. So i shortened the wires i'd made and ran it straight off the alternator (closer to the lights at least, right?). Disconnected the dimming resistor too (found the plug, aye)

 

It works as it should. Honestly I think this idle weirdness is just a red herring mixed with my over-sensitivity for running issues at the moment.

 

I measured the voltage drop over the old wiring at 1.85v and over the new loom at 0.97v. Did it in the day so can't tell the difference in terms of light but that should be a fair bit brighter eh. Got 13.6-odd volts at the bulbs now, same as at the battery when the alternator is running.

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