Thread: Headlights affecting temp guage 300Tdi

The temp gauge is earthed to the body. The engine needs the earth cable to the body repaired or replaced so that the headlamp current from the alternator doesn't raise the engine block voltage relative to the body. Also check your dash earth is working, as sometimes a dash light will also create a voltage drop relative to earth.

Originally Posted by bee utey

The temp gauge is earthed to the body. The engine needs the earth cable to the body repaired or replaced so that the headlamp current from the alternator doesn't raise the engine block voltage relative to the body. Also check your dash earth is working, as sometimes a dash light will also create a voltage drop relative to earth.

Excellent explanation. Thanks for that.

I just started gaining 1/8 tank on fuel gauge every time I turn on lights- so I've been driving around with lights on alot- sounds like same sort of problem
Brett
110 300tdi

Definately a common defender earthing problem, try an extra earth strap from the battery neg to the bottom of one of the seat bolts that protrude into the battery box. Defenders can suffer from this if used off road lots or in damp/ tropical environment. It is caused by a breakdown in the earth 'connection' between panel to panel and chassis.

That extra earth can also make a lot of difference to the heater blower motor control etc

JC

My tacho used to gain 1000rpm when the lights were on. I solved that by an extra earth inside the binnacle. This on a RRC, discos should be a little better done than mine.

On the Defender the earths from the gauges are grouped with several tags under one of the nuts holding the gauges in place. If this nut is loose, this will give the symptoms described. Less likely is the earth between the binnacle and the bulkhead and the earth between the bulkhead and chassis. The battery is normally earthed to the chassis, but if it has been earthed to the engine, a poor connection engine to chassis can also cause it.

John