Fog lights not getting power, What else to check? |
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Fog lights not getting power, What else to check? |
saigon71 |
Dec 15 2018, 01:27 PM
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#1
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Advanced Member Group: Members Posts: 2,000 Joined: 1-June 09 From: Dillsburg, PA Member No.: 10,428 Region Association: MidAtlantic Region |
My fog lights don't work on either side. After trying different bulbs, I tested for power with a VOM - no power. Next, I swapped the fog light relay out with several others...still no power.
What are the next logical things to check? Do the fog light switches go bad? Thanks. |
Spoke |
Dec 27 2018, 07:14 AM
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#2
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Jerry Group: Members Posts: 6,991 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
Here's a simplified schematic of the foglight circuit for a '74 914 as detailed in the Haynes shop manual.
There are 5 main components in the foglight circuit: o Foglight switch o Foglight relay o Headlight dimmer relay o High beam filament o Headlight switch To operate the foglights, the following conditions must be met: o The headlight switch must be in the headlight position (2nd click outwards) o The headlight dimmer relay must be on low beams. o The foglight switch must be pulled out. With conditions above met, current flow for the foglight relay coil goes through the headlight switch -->> foglight switch -->> foglight coil -->> headlight high beam filaments. The foglight relay coil shares 12V with the headlight high beam filaments. With standard headlights, the high beam filaments are much lower in resistance than the foglight relay coil thus most of the voltage drop is across the relay coil and the relay closes and foglights are on. If the headlights are high impedance LEDs, it is not clear if the foglight relay coil will energize. The foglights can be made independent of the high beams by removing the wire from pin 86 of the foglight and attaching it to ground bypassing the high beam filaments. Attached thumbnail(s) |
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