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Hi, sorry if Iv posted this in the wrong section please let me know if I have and I'll remove it and re post in the correct section.
Iv been working on a Citroen relay van which I found to have a bad ground connection from the battery to the body.
I put my scope on the battery negative post and a pcm ground and it showed 2.5 volts. I did some different things like turning the engine over and turned on the lights and at times the voltage reading dropped below 0v I think it went to -0.5V.
My question is how is this possible ? I realise the meter measures voltage difference but I don't see how voltage anywhere can be lower than the battery negative post? I did have the com lead on the battery negative too not the red lead before anyone asks.
without a good ground you will see voltage on ground side maybe review ohms law and power and ground integrity testing I believe on a computer ground you don't want more that..1volts
Thanks for the reply, I realise I had a bad ground(which I fixed and the van is now fine) and I understand why you would see voltage on the ground wire with a poor ground, I just don't understand how my scope showed me minus numbers? Maby I should just concentrate on fixing the problems but I just don't feel I fully understand the numbers I was seeing?
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