Turn on headlights, water temp guage goes NUTS!

What's up with this? Been messing with the lights (I no longer get dash lights when I step on the brakes!). All is mostly well, except this minor problem. When I turn on the headlights, my temp guage (this is a guage dash, real temp guage in a '71 Sprint) goes way past 250, like my fuel guage did before I fixed the sending unit.

Please don't tell me my printed circuit is shot; I don't want to hear that!

ADVthanksANCE...

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Cecil Hawkins
San Diego, CA
1971 GMC Sprint
The Project
All I need is time...and some $$$
"Tourist, go home! And take someone with you!"