Weird Alternator problem

[Hymie]

Since the dash was unceremoniously pulled apart by an Auto Elec trying to fix a wiring fault I've had a weird problem going on with my Defender.
Mine has an after market Tacho fitted and now it only works intermittently and last week I had a flat battery one morning. The battery is charged now however the Tacho fault persists. I've checked all of the accessible connections and all seems OK. Is there something in the Alt that could be causing the problem?
Please be gentle with me, I'm not good with electricals but I'm keen to do it myself as I have to learn.

[rainman]

Firstly I should say I'm not that good with electrics either! But I have played with tachos in Defenders a bit.

When you say you've checked all of the accessible connections, do you mean you have pulled off the instrument binnacle and checked behind the tacho?

The tacho would normally wired so that it is getting it's power (positive) from the same source as the fuel and temperature gauges (green wire), and the same would go for earth (black wire naturally). If they are not having the same problem then in theory any "power" issue would be basically behind the gauge. Check that the positive, earth, and feed from the alternator are on the correct terminals on the gauge. Is it possible for + and - to be put on opposite and cause a slow leak to earth through the gauge (and drain the battery)? Tdi Defenders don't use much power to run so a charged battery could last a reasonable while if you're not running high powered things like headlights or the starter.

The feed from the alternator is just a single wire straight through so as long as it's connected properly at either end there's not much that can go wrong there. Test the wire with a multi-meter?

Failing all this, it could be the alternator, but this is where my knowledge stops. If you rip it off and take it to an auto electrician they should be able to hook it up on the bench and tell you straight away if it's charging or not. Or, can anyone advise on how to test it yourself with a multi-meter?


James.