Engine temp. and headlights

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Sep 30, 2004 | 11:45 PM

rioghalmo

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Freshman User

Joined: Jul 2004

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Engine temp. and headlights

I just put in a replaced my 300 with another 300 in my 79 150. My engine temp. reads normal when my headlights are off but buries the needle in hot when I turn them on. Which temp. is right and what is goin on? thanks.

Oct 1, 2004 | 01:53 AM

paragod

Senior User

Joined: Mar 2004

Posts: 198

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From: Rocky Point, North Carol

I would check your sending unit wiring and make sure nothing's crossed. You can also check the temp at the radiator with a temp gun. Sounds like a crossed wire or ground problem.

Oct 1, 2004 | 09:52 AM

hdgapeach

Elder User

Joined: Jan 2004

Posts: 767

Likes: 1

From: Franklin, GA

Any similar reactions from the other guages, like oil pressure increases? If so it's the instrument voltage regulator on the back of the instrument cluster. If it only affects the temp guage turn the headlights off and turn on another accessory like the heater blower motor, windshield washer, radio and see if the same results happen. If it only occurs with the headlights, there is a conflict between the headlight circuit and temp circuit.