Voltages

[PhilNW 44]

Simple question, If I am getting roughly 14.4 volts on the battery when engine running and charging, what voltage can I expect at say the headlamp bulbs?

 

Got the impression the headlights look a bit dim, (compared with modern lights) allowing for the fact that the car is 30 years olds 

 

Got Osram Nightbreakers bulbs and earths are good (< 1 ohm) 

 

 

Edited February 12, 2023 by PhilNW

[DamirGTI 342]

Should be near the same voltage as on the battery .

 

Checked/cleaned the earths for the headlights ?

 

To test how much there's loss of voltage in the loom , impacting headlight illumination quality , park up against the wall or similar outside at night or in the garage with garage lights off .

Take an piece of wire , switch on the lights and bridge/connect directly from battery positive to the top horizontal bulb terminal - then you'll see how much illumination you're losing if the lights then brighten up (very likely they will , depends how much % , the worst the wiring loom state the higher % difference) .

 

Pretty common problem , because of the old degraded often oxidized wiring and connections made without moisture insulation ...

 

Best solution is cutting off majority of the OE headlight loom in the engine bay and wiring up the headlights separately via two relays .

 

I've done that on a few 205's including mine , and the difference is now really significant , so much better lights like on a modern cars .. added also an pair of Phillips +130% "Extreme vision bulbs" they're really good and long lasting , definitely not a gimmick , thus i recommend especially if you often drive at night .

 

D

[PhilNW 44]

Thanks for that Damir

 

I had taken some voltage readings previously and thought something was wrong. Repeated them today and losing about 1 volt between battery and headlamp connector.

 

Without Engine running Battery @ 12.4, main beam supply 11.4

Spots with direct supply from battery through a relay, nominal voltage drop.

All  Earths rechecked and less than 0.2 ohms. 

Not done the direct feed from battery to headlights but looks like a partial rewire is called for.

 

 

 

 

 

[Gaz D 6]

That sounds about right for voltage drop. Only 12volt and 0.5mm cable? Powerful lamps  fed from fuse box to stalk them to lamps

[petert 587]

Add a relay close to lights/battery to minimise the voltage drop.

[PhilNW 44]

Where is the best place to take new feeds (say 10 amp min) from, i.e. fuse box? At the moment I have the spots wired direct to the battery terminal  

 

Looking to tidy the wiring a bit

Edited February 14, 2023 by PhilNW

[welshpug 1,657]

Ring terminal from Shunt box into a fused relay would be easiest.

Edited February 14, 2023 by welshpug

[PhilNW 44]

3 minutes ago, welshpug said:

Ring terminal from Shunt box into a fused relay would be easiest.

Which/Where is the shunt box?

[PhilNW 44]

6 minutes ago, PhilNW said:

Which/Where is the shunt box?

OK found it, wondered what that box was called..

[Spesh 31 1 Cars]

Are those voltages you measured with it under load? 

[PhilNW 44]

 

3 minutes ago, Spesh said:

Are those voltages you measured with it under load? 

Took those readings without load to assess the condition of the wiring.

 

Since measured the resistance of the wiring from the battery through the switch to the bulb connector and got 0.4 ohms  

[Spesh 31 1 Cars]

worth measuring it with a load on it, you'll likely find a sgnificantly worse volt drop

[PhilNW 44]

2 hours ago, Spesh said:

worth measuring it with a load on it, you'll likely find a significantly worse volt drop

It was worse, which is I asked the question in the first place .. Did not quite believe the number I got..

 

Dont you just love 30 year old French electrics.

[Spesh 31 1 Cars]

4 hours ago, PhilNW said:

It was worse, which is I asked the question in the first place .. Did not quite believe the number I got..

 

Dont you just love 30 year old French electrics.

I'm not entirely convinced they were up to much 30 years ago when new lol :p