make or break relay

[scottbott]

if wired up to vehicle and a multi meter is put onto posts 30 and 87 without the engine running should there be power showing on both of the posts,mine is showing power I thought it would show power to both only when the engine is running?,have not checked the trigger wire yet as too dark,the earth is good

[CovKid]

Yes, since each is directly connected to the positive terminal of each battery. They are independent/separated until the relay is energised by trigger signal at which point they are connected together. Hopefully diagram below will show how it works. The idea is that only starter battery is available during starting (no signal from trigger) but as soon as engine fires and alternator kicks in, the leisure battery also gets charged because the relay has linked them together (trigger live).

With engine off, if you put your black tester wire to chassis, and touch red tester wire to 30 and 87 in turn, you should find the voltage is slightly different as you're taking a reading from each battery. Digital meter more accurate in this instance.

[scottbott]

I am only using one battery that is for my webasto,on hook up it is getting charged fine but when I start the engine it is not showing ant charge,have a feeling I did a crappy connector on the trigger wire will redo it on saturday and have a good look at it,too dark when I get home

[scottbott]

been out playing around and when the engine is running the relay is not switching on,I have a "power probe" thing by Sealey for powering things up and checking out if connections are good,I connected this to my leisure battery with the engine running and when I connect the "earth"connector to the earth terminal of the relay it clicks and my battery is getting charge,disconnect and nothing,I have checked all of my leads for continuity and all is fine,changed battery earth leads and nothing,changed battery terminals if I put a lead from the leisure battery it clicks in straight away.The earth point is a brand new 12 connector negative busbar from 12 volt planet,it does not seem to be getting an earth from the battery right next to it,something so simple is doing my frigging head in