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Temperature Gauge Wiring

Gmilburn

Member III
The previous owner of my E29 had disconnected the Water Temp gauge for the Universal A4--as he believed it had a short. I have searched the web for a wiring diagram for the four terminals on the back of the gauge--with no luck. I actually tried to remove the gauge from the panel but it seems to be corroded in--and I was unsuccessful, with even gently using a pipe wrench to twist it out. Sooooo, before I tear it up getting it out and rebuilding another control panel, I wanted to try one last time to salvage the gauge.

There are four posts--and Im sure one goes to the temp sending unit from the A4--and one goes to positive and one to negative. But which is which? And the fourth post?

If anyone knows how I might hook it back up to test it--Id appreciate it. Otherwise I will have to tear it out, order a new gauge and sending unit from Moyer Marine and start fresh.

I've enclosed a couple pics to assist in the endeavor.

Thanks in advance.
 

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treilley

Sustaining Partner
It definitely had a short with any power connected to either of the central posts.

The two tall center posts are for mounting. Normally there is a U shaped piece of metal that had 2 holes in it. See photo. The two at the top are connected to the sending unit and the ignition switch(on position). Look for some markings on the back of the gauge. One may be marked "S". This is for the sending unit. There should be no ground. If it does not work, connect a ground to one of the central posts.

swback_lg.jpg
 
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mherrcat

Contributing Partner
The gauge usually has an aluminum bracket that holds it in place; I believe I can see one at the edge of your pic on the other gauge. As noted, the bracket may be missing and something connected to the mounting studs, which probably have no electrical purpose.

You can probably whack the gauge out of the panel from behind, but before replacing the gauge I would try to get it wired up correctly to see if it works; it may be fine.
 

treilley

Sustaining Partner
Now that I look a little closer, just remove that red wire and see what happens. That is probably the short.
 

jkenan

Member III
I pulled my A4 panel out this past weekend to rewire it at home (since the original wire is now 30 yrs old - might explain why your PO thought there was a short). I was actually studying all guages and their wiring last night to understand them before disconnecting everything. I'll take a photo tonight of the back of the temp guage and post it for you, along with labels for the different connections.

Might be tomorrow before I get it posted.
 
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