Headlight Wiring

meego · Nov 17, 2021

I’m having a nightmare with this. Fitting new headlights. Standard Wipac replacements so nothing fancy. Connected to existing wiring and only getting a dull light on dipped and no main beam. I’ve crimped new connectors on the three wires going to the bulb, I have a good known earth, checked power to bulb with a test light and it’s fine. Still getting only a dull dipped beam. Also tried a new bulb with same result. Any thoughts ??
Edit. Should also say I’m only on the drivers side. Near side is original and looks fine.

marjon · Nov 17, 2021

Check fuses, I had a really manky burnt fuse would only light the bulb dim although it all checked out ok at the light itself. with a meter.

J

kermit_rr · Nov 17, 2021

wipac is an LED replacement? it could be duff internal circuitry. can you try a regular bulb as a test?

meego · Nov 17, 2021

marjon said:
Check fuses, I had a really manky burnt fuse would only light the bulb dim although it all checked out ok at the light itself. with a meter.
I only done a visual on the fuses. I’ll try cleaning up the terminals. Cheers.
J

kermit_rr said:
wipac is an LED replacement? it could be duff internal circuitry. can you try a regular bulb as a test?

These are standard mate. The kit came with a halogen bulb

kermit_rr · Nov 17, 2021

ok in that case i'd suggest checking the voltage at various places around the circuit. from the positive terminal, to the positive at the bulb.. then the negative at the bulb.. any connections inside the unit you can see.. then do the same with earth and see if there are any discrepancies

meego · Nov 17, 2021

kermit_rr said:
ok in that case i'd suggest checking the voltage at various places around the circuit. from the positive terminal, to the positive at the bulb.. then the negative at the bulb.. any connections inside the unit you can see.. then do the same with earth and see if there are any discrepancies

Ok. Engine running or not running ?
I did check the voltage at the terminals where the headlight wiring connects to the loom and I was getting a low reading on both main and dipped. With the test lamp at these terminals I’m getting a dull light on the main beam wire even when it’s not switched to main beam at the light switch ??

kermit_rr · Nov 17, 2021

meego said:
Ok. Engine running or not running ?

wont matter, but you dont want to flatten the battery

meego said:
I was getting a low reading on both main and dipped. With the test lamp at these terminals I’m getting a dull light on the main beam wire even when it’s not switched to main beam at the light switch ??

sounds like a dodgy connection somewhere
disconnect the main beam wire, does it still have a reading? does the mainbeam connector on the lamp have a reading?

marjon · Nov 17, 2021

meego said:
I’m getting a dull light on the main beam wire even when it’s not switched to main beam at the light switch ??

Sounds like an earth.
Is this the same on the both sides?
Could be switch or stalk.
Need to work you way along the system to find out where the voltage changes.

J

kermit_rr · Nov 17, 2021

marjon said:
Sounds like an earth.

its always earth

apart from when its not, just to trick you.. then its earth somewhere else

meego · Nov 17, 2021

I’ll head out after work and follow both of your advice and let you know.

doriz · Nov 17, 2021

When I did this job I renewed all the earth cables too. The difference was very noticeable.

meego · Nov 17, 2021

doriz said:
When I did this job I renewed all the earth cables too. The difference was very noticeable.

There’s an earth in the loom that goes through the wing, but I’m thinking of earthing everything to a good earth point on the very front bolt of the inner wing. Does it matter where it’s earthed as long as it’s good ?? Could I also earth the loom black wire to that point ??

doriz · Nov 17, 2021

meego said:
There’s an earth in the loom that goes through the wing, but I’m thinking of earthing everything to a good earth point on the very front bolt of the inner wing. Does it matter where it’s earthed as long as it’s good ?? Could I also earth the loom black wire to that point ??

I earthed mine to the coolant cradle, behind the bolt. Just find somewhere close that has a good conductivity.

meego · Nov 17, 2021

doriz said:
I earthed mine to the coolant cradle, behind the bolt. Just find somewhere close that has a good conductivity.

I’ve just rebuilt the full offside front corner. When I was putting everything back together I made sure every touching face was well coated with paint to slow the tin worm down, but the downside is finding good earth

Disco1BFG · Nov 17, 2021

meego said:
. With the test lamp at these terminals I’m getting a dull light on the main beam wire even when it’s not switched to main beam at the light switch ??

Sounds like one of the headlamp switches is kaput for you to get this crosstalk ... either the stalk switch is fubar - or the main switch - both are pretty notorious for such "features"

meego · Nov 17, 2021

Disco1BFG said:
Sounds like one of the headlamp switches is kaput for you to get this crosstalk ... either the stalk switch is fubar - or the main switch - both are pretty notorious for such "features"

I didn’t manage to get on it tonight. Tomorrow the plan is to ensure good earth, then start from the switch and work my way forward with the MM to see what I find. I’m assuming as it’s a 12v bulb I’m looking for at least that reading all the way ??

marjon · Nov 17, 2021

meego said:
I didn’t manage to get on it tonight. Tomorrow the plan is to ensure good earth, then start from the switch and work my way forward with the MM to see what I find. I’m assuming as it’s a 12v bulb I’m looking for at least that reading all the way ??

Yes.

I don’t really know how to explain this right but will try.

Check the first point, then skip a few, then skip a few.
That way you can skip the hard to get to connections until you find the problem then back track.

J

Disco1BFG · Nov 17, 2021

meego said:
I didn’t manage to get on it tonight. Tomorrow the plan is to ensure good earth, then start from the switch and work my way forward with the MM to see what I find. I’m assuming as it’s a 12v bulb I’m looking for at least that reading all the way ??

Yep - main feeds to switches should be more or less battery voltage - decreasing slightly as the circuit gets longer - but only by a tiny bit - less than 0.5 V loss ...

It can be helpful to load the circuit with an appropriate load - I.E. a headlamp bulb (!) - connecting it temporarily at various points in the circuit, it should quickly show you where the issue is ...

There's a guy on the tube who is really good at electrical troubleshooting, and even better at explaining it too - here's one of his for your perusal....

he's got plenty more

Dr Strangeglove · Nov 18, 2021

Disco1BFG said:
Yep - main feeds to switches should be more or less battery voltage - decreasing slightly as the circuit gets longer - but only by a tiny bit - less than 0.5 V loss ...

It can be helpful to load the circuit with an appropriate load - I.E. a headlamp bulb (!) - connecting it temporarily at various points in the circuit, it should quickly show you where the issue is ...

There's a guy on the tube who is really good at electrical troubleshooting, and even better at explaining it too - here's one of his for your perusal....

he's got plenty more

Well for someone like me that doesn't have a scoobie about electrics, that was really informative. It also shows why electrics would be the killer for older cars (unless of course the low emission zones kill them first!).

meego · Nov 18, 2021

Disco1BFG said:
Yep - main feeds to switches should be more or less battery voltage - decreasing slightly as the circuit gets longer - but only by a tiny bit - less than 0.5 V loss ...

It can be helpful to load the circuit with an appropriate load - I.E. a headlamp bulb (!) - connecting it temporarily at various points in the circuit, it should quickly show you where the issue is ...

There's a guy on the tube who is really good at electrical troubleshooting, and even better at explaining it too - here's one of his for your perusal....

he's got plenty more

Excellent video. I don’t think I’ll need to bother worrying about a BCM on my 90 though

I’ll be checking out more of his stuff for sure. Cheers.

Headlight Wiring

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