Dash turn signals |
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Dash turn signals |
Cal |
May 24 2016, 05:08 AM
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#1
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Senior Member Group: Members Posts: 615 Joined: 19-November 14 From: Philadelphia Member No.: 18,138 Region Association: North East States |
Question.....when I turn on the turn signals in either direction both indicators on the dash board light up at the same time. Any idea what the problem might be?
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toolguy |
May 24 2016, 08:54 AM
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#2
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Senior Member Group: Members Posts: 1,270 Joined: 2-April 11 From: San Diego / El Cajon Member No.: 12,889 Region Association: Southern California |
You're probably going to find this hard top believe, but check the wattage of the bulbs in all four corners. .
I had this happen when I installed all new bulbs. . After a couple of hours of checking grounds, connectors and circuits, I traced it down to not using the correct wattage bulbs. . Once I put in the old original bulbs the dash indicators worked correctly again. I never figured out the 'why' of it and chalked it up to the old military electronic explanation that always applies. . "PFM". . Pure F-ing Magic. . |
Spoke |
May 25 2016, 09:57 AM
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#3
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Jerry Group: Members Posts: 6,992 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
You're probably going to find this hard top believe, but check the wattage of the bulbs in all four corners. . I had this happen when I installed all new bulbs. . After a couple of hours of checking grounds, connectors and circuits, I traced it down to not using the correct wattage bulbs. . Once I put in the old original bulbs the dash indicators worked correctly again. I never figured out the 'why' of it and chalked it up to the old military electronic explanation that always applies. . "PFM". . Pure F-ing Magic. . I can take a bit of the PFM out of it for you. See the diagram below with the flasher in the top right corner. Notice the 2nd small coil. When heavy exterior bulb currents flow when the flasher is flashing, the secondary coil connects the "K" lead to 12V. The K lead is connected to a common wire between the dash indicators. When the heavy exterior bulb current flows, the K lead connects to 12V, thus one of the dash indicators has 12V across it and lights while the other indicator has 0V across it and is off. 2 scenarios cause both to light: 1) Exterior bulb current is not enough to close the secondary relay; both indicators flash at 1/2 voltage. 2) The secondary coil loses its efficiency over time and heavy exterior bulb current doesn't close the secondary relay. My flasher suffered from the 2) issue. On the first flash, only the correct indicator lit, then on subsequent flashes, both indicators lit. I solved this by removing the common wire between the indicators from the K lead and attached the common wire to tach ground. This is a common fix. If you do this fix, you'll find the opposite indicator lights. (RT indicator lights with LT side and visa versa). Swapping the bulbs and bulb holders LT to RT will solve the opposite indicator issue. Attached image(s) |
Dave_Darling |
May 25 2016, 04:03 PM
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#4
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914 Idiot Group: Members Posts: 14,991 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
2 scenarios cause both to light: You forgot one scenario: Your early 1974 914 has a wiring harness that is only set up to have one turn signal indicator in the tach. It also has a leftover early-style tach with two arrows in it. So the guys at the factory spliced in another section of wire to daisy-chain the two arrows together so both light up at the same time. I'm pretty sure this is the OP's issue, because he mentioned he had an early 74 car. --DD |
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