My cooling and oil temp gauges move when headlights come on

Mike

Mine do that too, but much less. I am not an electrician, but I could imagine the reason being the single ground for both instrument functions, the actual readout and the instrument's lighting. The readout is always using the ground, when you switch on the lights, additional current flows through the same wire, and probably changes the available capacity for the instrument's ground, therefore moving it slightly.

Maybe an electrically unchallenged member could chime in?

Cheers
Urs

 

It is a special feature of most older Italian cars, consider it your headlights on indicator, it is also useful to help you practice your gauge reading discipline and cause a slight elevation for your heart rate when you notice it as we all know that watching the gauges is something you have to do in old machines. : )

 

I had a Porsche 924 that read hot when it wasn't. I thought it was overheating, so I changed the water pump, coolant etc. Then realized it was electrical and changed out the alternator and battery. After everything else was changed, I realized the one thing I missed was the large ground wire between the motor and the frame. Changed that out, and all of my electrical and "heat" problems vanished forever.

 

Paul might be right, When I was doing my shift shafts seals I noticed that the ground cable is just near the speed sensor and was totally corroded as it is on the same level of your lower frame. This easily gets wet/moisty and if, sort of speak, it is not protected by leaking engine oil, nature elements take control.

I don't know if I had this issue as at the time I was doing a lot of maintenance before I could drive. I took it off and cleaned it. I could not find any bare metal anymore on the ends of the ground cabel when I took it off.

I'm not sure if this would fix it, but what Paul is saying could makes sense of what I saw with my ground cable.

HTH
MvT

 

Totally agree with everyone. When I recently had mine up on the lift when I had the new oil cooler fitted, I noticed the engine ground which is a thick braided wire was totally covered in dirt and oil where it bolts on the chassis and engine. It's only a short thing, about 6 inches and looks easy to do if you can get underneath.

It's on my to do list when I get the chance and seems quite cheap to buy.

 

Re-doing the engine ground didn't change anything re the instruments moving with the lights on, on mine...

 

I just went for a drive and checked ours. The coolant gage moves up about a needle width when the lights are switched on. I'm guessing it's the voltage regulator and totally normal.

Dave

 

My gauges also go up when you turn lights on. I know I had my alternator checked. Is there a diagram from all grounds?

 

hmmm, i wonder if this is why my dash lights dont work. I no longer have my lifts so can someone tell me which side it is on when looking at the ass end?

 

Mine also does it, if I am running low on fuel I switch the headlights on and hey presto more fuel in the tank.

 

Same thing happens on my 328

 

hehe, Design bugs

I checked mine after 1hour drive and I do not seem to have it I'll go to the dealer, because this isn't right! Strange as I do not have a new fuse box or other new wire replacements other then my ground cable and new battery lines.