Fitting led lIght bar - Large Voltage Drop

[Lexlee]

Hi,
Just tried it, light bar works, take it the relay is goosed?

 

[westward10]

Possibly, it either needs testing or replacing. Can you see the switch rating of it.

 

[Lexlee]

Yes it clicks when power applied, rated at 40 amps..

 

[davesparks]

Hi,
Sean_ork... Have run a cable to Earth on battery.... No change
Connected earth back up then ran pos from light to battery it lights up. So I assume the earth is ok?
Davesparks ...... The cable (just used micrometer First time in years) is 3.5 mm and is rated at 17amp says he got it from H..fords. The earth for the relay he's has connected that to the original earth for the vehicle horn (air horn fitted drivers side) and also connected the earth from the light bar to the same point as the relay earth ( original vehicle horn)

3.5mm, is that the diameter? Conductor size is measured in square millimetres, I don't add the squared part as I'm not sure how on the iPad and everyone here understands how cable size is measured. I've just looked up automotive cables an 1sqmm cable is rated around 17A.

The earth point near the horn seems quite a distance from the usual places to install a light bar, could you not get a connection to the bodywork anywhere closer to the light bar?
The two possibilities I can see for this are either a high resistance connection or voltage drop, check that all connections are clean and tight and measure voltage at every point of connection with reference to the battery -ve to see where the voltage drops in the circuit.

 

[Lexlee]

Hi Dave,
Sorry forgot to mention light bar is at front in A-Frame in front of where it says Defender on the slam panel.

 

[westward10]

You have confirmed it functions when you bypassed the relay so the issue must lay there.

 

[Lexlee]

All wire and connections are new. With the bar disconnected there is 12v at the supply to bar, with it connected without the link in mentioned above their is 3v at the same point, there's only 1foot of cable to the light bar from that point.

 

[davesparks]

Hi Dave,
Sorry forgot to mention light bar is at front in A-Frame in front of where it says Defender on the slam panel.

Ok, I've got a pair of spots mounted to the A bar on my defender, each one is earthed directly to each spot's mounting bolt onto the A bar.
If it's the new plastic A bar then I'd probably go for one of the bolts which hold the bumper to the chassis rail at the bottom of the A bar.

If I remember rightly the horn is earthed to the inside of the wheel arch that it is mounted to, I'd not be keen to put a lot of current through that path.

 

[davesparks]

Having read the rest of the thread then I'd say Westwood has your answer, if it works when the relay is bypassed then the relay is probably goosed