Temp alarm and Temp gauge fault

1984 Mk 1 Golf Cab
 (Please
Hi
Need some more help
See photos
1, Dash High temp alarm, check the rocker cover earth seems fine, expansion tank connection seems fine, but how do you verify the expansion tank alarm,, Open circuit or short circuit, not sure of the overall circuit functionality.

2. Temp Gauge 0-150 Deg (Not sure if oil or water that is being measures 321919541 VDO)
Not sure if its been fully wired (My sons car) I have never seen the gauge work
Can anybody confirm the connections on the gauge, see photos

Depending on the year there may be a coolant level sender issue, as they can get Calcified and not register correctly.  For the senders you have to have a 50/50 blend of A/F to Distilled water other wise it can flash the light.  A light fully on and no deflection is usually the cap on the gauge (internallly) or cold solder joints.

Also the Temp gauges are "iffy" at best the older they get.

They are prone to a Capacitor failure on the pcb, as well as cold solder joints on were the wires attach to the gauge posts.  I can't remember the specific value of the Cap…Maybe Rubjohnny does of the top of his head.

If you have replaced the Coolant, and didn't take time to BURP the hoses to remove the Air Bubble from hades, then you may have a temp sender that isn't touching the
coolant.

To prevent this you fill the Radiator from the upper hose then the block from the upper water outlet.  Going forward you should drill a 1/8 hole in the lip of your t-stat to prevent this.

In the signature I have a link to the how-to's that I have made over the years, and there are a couple about flaky water temp gauges.

Capacitor is 10uF, replace with a tantalytic bead instead of the electrolytic. More reliable.

The separate gauge in the 1st picture is for oil temperature, coolant gauges only go up to 120 and oil are 150.

I guess the oil temperature gauge has not been plumbed in as there is already a oil temperature display on the MFA.