How to tell if the polarity has been reversed?

[TigerMoggie]

I went to help a friend try and get their car running. He'd taken the battery off to charge it and I noticed the earth was connected to the -ve terminal. I asked him if/when the polarity had been reversed and he didn't think it had. The car cranks over but won't start, there is fuel and a spark from the coil (a bit weak looking). Both fuses had also blown and none of the ancillary electrics work, although I did find one of the braided wires had come off the fuse panel connector (are the braided ones on older cars all earths by the way?).

If the battery were connected wrongly what if any damage can ensue? Or if we don't know the actual polarity of the car now, would flashing the dynamo correct it anyway? And for "originality" purposes should it be put back to +ve earth.

Appreciate your assistance.

[bmcecosse]

Leave it as is - polarity has no effect on starting......

[simmitc]

You can make the polarity whichever you want, with the battery connected, just re-polarise the dynamo. If it's had an alternator fitted, then it will almost certainly be -ve earth.

[mike.perry]

All earth wires are black with the exception of the thick black cable from the battery to the starter solenoid then starter motor. The thick braided wire from the battery to the car body is also earth.
When you have checked the wiring and replaced the two 35 amp fuses in the fuse box and 10 amp in line fuse then your ancillary electrics should work.

[bmcecosse]

Noted that error has been corrected.

[Alec]

Hello Tiger,

the polarity will make a slight difference to the spark if the coil hasn't been reversed. With the battery connected -ve earth, then the coil terminal to the distributor should be - (or sw if an old coil). This ensures the best spark.

BMCE, I don't think it's necessary to shout, we all make mistakes and it's very easy to mistype what you meant, surely a simple correction is enough?

Alec

[bmcecosse]

Alec - it was completely wrong advice and if followed by others could cause ruined alternator/wireless. And yes - of course the coil should be connected the correct way round depending on polarity - but the engine will still start either way round - and so I was keeping it basic here !

[simmitc]

Alec, thanks, couldn't have put it better myself. The annoying thing is that I spotted a typo in that I'd put "1ve" and attempted to correct it to "-ve" but ended up with a plus instead of a minus. It is a problem with these keyboards that don't understand what the fingers mean.

BMC - I have corrected the typing, so perhaps you would like to delete your reference to avoid any confusion.

[bmcecosse]

Yes - will gladly do so... It's important advice and needs to be correct.