I have a 2000 F250 SD reg. cab, that I swapped the 7.3 from an OBS. I have aftermarket Auto Meter phantom series gauges on a piller. Lately Iv noticed that if I put a demand on the electrical system (blower motor on high, head lights on, etc) that my temperature gauge goes from around 190+/- to 200 instantly. I find this very strange and I'm looking for some suggestions. The gauge is electrical and uses a 5 Volt reference signal to measure temp. My temp. Gauge on the dash is unhooked because it never read right, hence the after market gauges. The batteries are both fairly new and the alternator works just fine. I'm wondering if maybe this is a sign of a weak alternator, or something along those lines. Also Iv noticed every now and then if I turn my headlights on while driving the radio will suddenly turn off for a second and turn back on. i have done all the work on the truck and fairly mechanically inclined but I'm lost at this point. Any help would be appreciated. Thank you!