car electric question

stranger12

hi guys,

why when you do a continuity test from some fuse to another fuse it seems to have a connection or even to the chassis ( ground) which soon changes when you open the ignition?

wildmandy

Huh? What?

Rain_Shadow

Try asking on the 'Motoring' board.

But, TBH, you may have to try harder with your question.:rotfl:

forgotmyname

Because your item is earthed..

eg..

EARTH --- BULB --- FUSE --- SWITCH --- BATTERY +

Connect one lead from the meter between FUSE and SWITCH and the other to earth and you have a circuit.

SWITCH on and you still have a circuit but the bit between the FUSE and SWITCH is not 12v positive.

stranger12

What i mean is i you take a multimeter and use continuity check, you can that almost all of the fuses have contiunity to each other which i don't understand

This sometime changes when you switch ignition on

thescouselander

forgotmyname wrote: »

Because your item is earthed..

eg..

EARTH --- BULB --- FUSE --- SWITCH --- BATTERY +

Connect one lead from the meter between FUSE and SWITCH and the other to earth and you have a circuit.

SWITCH on and you still have a circuit but the bit between the FUSE and SWITCH is not 12v positive.

Add to that, more often these days, a lot of stuff is wired using a switched earth:

EARTH --- SWITCH/ECU ---- DEVICE --- FUSE --- +VE Feed

Basically when an ECU is switching in a device it often completes the connection to ground.

In this case many of the fuses will be wired to a common +ve bus which is why you get continuity between them. Continuity testers are designed to be used on de-energised circuits which is why you're getting strange results with the ignition on.