Gauge wiring questions Options

[lmcchesney]

I'm trying to add a temp gauge and ammeter meter to the 914. The gauges are from the FLAPS and not VDO's.
The temp gauge and sender instructions says to insert the sender into head source with wire connected to back of gauge. I wanted to test the gauge and be sure the readings are correct. My understanding of these gauges are that they produce a mV current which is read by the gauge. Thus, I'm thinking the sender creates the current but you need a ground (casing of the sender and case of the gauge) to complete the circuit. Thus for a test I placed a jumper cable from the case of the sender to the case of the gauge. Placed the sender in boiling water and waited. The gauge does not move after an extended period of time. Thoughts?
Also, the schematic for the ammeter describes connection of one of the poles of the gauge to the large amp wire from battery to the starter solenoid and the other pole to the "Hot Wire". My understanding is that the gauge is placed in line with alternator to the battery. What am I missing?
Thanks,
L. McC