Headlight harness upgrade

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Sam_C

Club Member
I’m finally getting round to putting relays into my headlight harness. In order to cut down on wire length and keep things tidy I’m planning to tap off the alternator at the battery lead connection rather than going directly off the battery. Can anybody think of any reason why this is not a good idea?
Ta
 
Rob Gaskin

Rob Gaskin

Treasurer
Staff member
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That will work because the alternator is connected to the battery anyway to charge it.

Don't forget inline fuses. Have you got a diagram sorted? I'm asking because the headlight circuits can be confusing.
 
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Sam_C

Club Member
Hi Rob. Thanks for that. Yup, two relays independently fused so there’s no single point failure path. Keeping the fuses as close to the supply as possible, and earthing the relay activation pins through the original wires back up to the dip switch.
I looked at all the various wiring diagrams out there plus my service manual wiring diagram to work out what was going on. A bit baffling at first but once you “get it” the changes become self-explanatory.
Having said that, my next post will probably be asking for help on replacing burnt-out wiring looms..
 
Rob Gaskin

Rob Gaskin

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Ok. You just have to operate the relays with the existing wiring and supply power to the headlights via new circuits through the relay contacts and earth the bulb as a normal car.
 
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Sam_C

Club Member
Lot of good info in there Zbloke, thanks.
As for making my new harness - is there anybody in the U.K. who supplies the Datsun-style 3-pin connector/plugs? I’ll put an ad in the wanted ads too,,just in case someone has passed this way before and has some spares.
 
zbloke

zbloke

Club Member
Your best option, in my opinion, is to contact "Minksport" on here and ask if he has any old wiring harnesses he can cut the correct OEM plugs off
 
Farmer42

Farmer42

Club Member
Recently converted mine using a universal H4 harness that plugs into the socket that fits on the back of the headlight bulb. The downside that I may need to overcome is the single point of failure if the fuse blows but I would still have sidelights which are part of the headlight unit and on a separate circuit. However, my reckoning is that if the fuse blows on a normal headlight circuit it would cut the dip beam and if that happened I wouldn't drive round with main beam on instead. I would use sidelights which is what I have. Cost me £13, I didn't have to cut anything and it looks pretty tidy. Mine uses the LH headlight as relay switch feed and the live runs under the inside of the wing in the engine bay to my battery which is on the LH side being a RHD car. Simples!
 
Rob Gaskin

Rob Gaskin

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Farmer42 said:
Recently converted mine using a universal H4 harness that plugs into the socket that fits on the back of the headlight bulb. The downside that I may need to overcome is the single point of failure if the fuse blows but I would still have sidelights which are part of the headlight unit and on a separate circuit. However, my reckoning is that if the fuse blows on a normal headlight circuit it would cut the dip beam and if that happened I wouldn't drive round with main beam on instead. I would use sidelights which is what I have. Cost me £13, I didn't have to cut anything and it looks pretty tidy. Mine uses the LH headlight as relay switch feed and the live runs under the inside of the wing in the engine bay to my battery which is on the LH side being a RHD car. Simples!
Click to expand...

Next time you are driving down an unlit country road at night try switching your headlights off. Perhaps my rallying days have influenced my thoughts.

Can you remember when cars only had one hydraulic brake circuit?

I still think the factory idea of the left and right headlights fed by different fused circuits is the best but failing that it's good to be able to have a back-up (dip or main).
 
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zbloke

zbloke

Club Member
You can always add more fuses and relays so RH and LH dip and main are all on separate circuits - so if your LH dip fuse blows, you'll still have LH main and RH dip and main

Proper rally car wiring, eh Rob? ;)
 
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Sam_C

Club Member
Farmer42 said:
Recently converted mine using a universal H4 harness that plugs into the socket that fits on the back of the headlight bulb. The downside that I may need to overcome is the single point of failure if the fuse blows but I would still have sidelights which are part of the headlight unit and on a separate circuit. However, my reckoning is that if the fuse blows on a normal headlight circuit it would cut the dip beam and if that happened I wouldn't drive round with main beam on instead. I would use sidelights which is what I have. Cost me £13, I didn't have to cut anything and it looks pretty tidy. Mine uses the LH headlight as relay switch feed and the live runs under the inside of the wing in the engine bay to my battery which is on the LH side being a RHD car. Simples!
Click to expand...
I think I’d be a bit wary of the quality of components in a £13 loom to be honest! But if it works...crack on Did you find a big difference to the light output?
I guess the point to be made about losing both dip and main beam.. you rightly say that you wouldn’t normally drive around on main beam but what a nice temporary back up to have if you lose the dipped when out in the middle of nowhere.
One thing is sure.. the lights aren’t going to fail as you potter along down Tooting High Street, but the minute you go touring in the Welsh hills.....
 
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Sam_C

Club Member
Thanks for the offer Nigel but I’ve already got my harness 3/4 made. Just waiting for my new plugs and I’m done.
 
Farmer42

Farmer42

Club Member
Sam_C said:
I think I’d be a bit wary of the quality of components in a £13 loom to be honest! But if it works...crack on Did you find a big difference to the light output?
I guess the point to be made about losing both dip and main beam.. you rightly say that you wouldn’t normally drive around on main beam but what a nice temporary back up to have if you lose the dipped when out in the middle of nowhere.
One thing is sure.. the lights aren’t going to fail as you potter along down Tooting High Street, but the minute you go touring in the Welsh hills.....
Click to expand...

I did consider the quality of the components but if it fails I just rip it out and re-install the original wiring. I had nothing to lose. The headlights work great and they are a lot brighter. The main thing is that it is taking all the load off the switch which was the reason for using relays with H4 bulbs. I may consider separating the different sides out or using separate feeds for dip and main beam but to be honest, I don't do an awful lot of night driving in the Zed. Thinking back to when I had the original bulbs in a sealed unit, they were not much brighter than the side lights I have now.
 
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