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Wiring headlights and driving lights.

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Bench testing a new loom and I’ve got almost all the way there with the light but slightly stalled and thought it wouldn’t hurt to ask for help. 
 

I have 3 switches. 
one for driving lights. 
One for headlamps 

and one to toggle main beam dipped beam. 
 

I have driving lights working ok on a relay. 
 

I have headlamps working ok with main beam dipped beam ok. 
The head Lamp works off a switch and relay. The relay then powers the second relay which toggles between main and dipped beam. 
 

all good so far. 
 

the challenge is I want to be able to switch on the driving lights independently AND have them come on IF the headlamps are on. 
 

I thought I could do this by taking the coil side of the headlamp relay and running that as a second trigger for the driving lamp relay (as well as the switch). 
 

as suspected that shorts  things out.  
 

Is there a proper way to do this? Maybe I need a fourth relay in the mix. 
 

ive added a truly awful diagram which worked until I added on the fancy part of triggering the driving lamp relay. 

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Solved

with 4 th relay 

 

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Only just seen this thread. If you need any more help let me know. This is what I do for a living lol. 

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Cheers mr Barry  

I think I’ve solved the lights puzzle  although there are w couple of bits need fine tuning  

ive got one fairly substantial wire for the main feed to headlights  

I’ve tried to do the right thing by isolating the switches and power to head lights via the relays. Is it ok to split that main feed out in order to power both the coil side of the relay and the switches power going through it? Or should I find a totally different cable to power the coil side? 

 

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I’ll do you a drawing later. 
 

what is the original wiring? You got a diagram?

not at home atm. 

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Thank you. Appreciated. The original loom is from a Sierra but I’m replacing it with a complete new loom because there were wires everywhere without a clue what they were doing. Random shorts everywhere. 
 

I’ve bought a 21 circuit loom which is good value but in reality not much more than wires laid out in bundles going through a fused box. 
 

No instructions but if I look at it long enough I’ve got most of it sussed I think. I’ve laid it next to the car and started it on the new loom so all good. Now I have the driving, headlight main and dipped I’m pretty happy although it feels messy at the moment joined together with blocks. 
 

the biggest challenge I think will be getting the brake light and reversing lights sorted. 
 

 

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Nothing complex about a car loom really.
 

As for head lights. Cable size depends on current, side lights use very little current they tend to be 5w so under 0.5 amps. Head lights are generally 55w IIRC so under 5 amps. Main beam 55W so under 5 amps. It’s 1 amp per 12 watts. 
 

Could you let me know what each of your lamp wattages are? 


side light:

dipped:

Main beam:

driving light: 

When exactly do you want them to operate? (Especially in relevance to each other and ignition) 

ill do you a drawing and quick explanation and post pictures for you. 
 

 

Reverse and stop lamps etc are a doddle. 

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Mr Barry, 

old loom out and new one in position. All going well so far. Could you advise on the alternator though please. Three wires on the previous loom.  Two thick brown and one thin blue. I’m presuming one thick to take the charge back to the look or battery +, the thin blue im presuming any ign live as an exciter wire and the other thick wrapped in yellow and green would be an earth? 

agree? 

yes, I should have put a multimeter on each of the wires before pulling the old loom out.  

B44B913A-F7DD-41CE-881C-576FEF12A281.jpeg

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DO NOT connect the thick brown wire to EARTH without checking.

This may cause a direct short and then you will want another loom or repair.

I would think that the wire had a bit of tape wrapped around to identify it from the other.

Normally alternators are Earthed direct to the mounting bracket.

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Also seemed a bit thick for an earth! 
 

so I can run it, but I don’t expect to get any voltage out of it until I put a 12v exciter into it right? A 12v exciter would only carry 12v low current from the ignition so it would be reasonable that’s the thin blue wire? Wish I’d tested them before taking it out. Another lesson. 
 

it looks most like an old Bosch alternator if anyone has anything similar. 

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Yes earth is via the mounting bolts normally. And the small with will excite the field. The larger wire will be the live feed to charge the battery. Make sure you have a clean earth because painting the mounting brackets is common web people want them to look nice, then they get no earth because they don’t clean the contact patches and it won’t work. 👍

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Makes sense. So what do you think the second thick brown wire with the tape on it is for? 

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Get a multimeter and bell out. It could be an earth. There’s no easy way to know on aftermarket looms how it’s been wired, everyone does it differently. Or connect a light bulb between the two and pop the battery on. Make sure they can’t touch earth or anything metal. If one is earth and one live you will have a light on. If not both will be 12v. You have to disconnect the light bulb before testing that tho or you will read 12v both sides of the bulb because there’s no earth puking it down. 

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So the middle thick wire is pushing out 14.5 volts

the other thick wire seems to pushing out 0.5 volts at idle. Although it did occasionally spike higher but that could have been my multimeter touching the other spade. 
 

so questions :

the wiring loom I am installing provides a cable to take that 14v back into the loom. However it does advise if the current produced by the alternator is greater than 80 amps then use a by pass wire to take the feed straight back to the battery. I have no idea what my alternator puts out and with only one set of hands it’s going to be challenging to rev the engine and measure current etc. Is the safest bet best to just take the 14v output from the alternator and run it back to the battery + directly to charge it? 
 

On the old loom there was a clip that looked a bit like a voltage regulator.  Having taken it apart it look so rusty I don’t even know if it was being used. I don’t know if the alternator has a built in regulator as I know more modern ones do. If I’m taking the output from the alternator back to the battery post, do I need to get some kind of inline regulator? 
 

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