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Speedometer repair help
I was driving the other day and smoke came out of the speedometer.
1987 911 Cab. Did some searching on this site and replaced the resistor on the speedo board. Also replaced the 100mF capacitor. Put the speedo back in and instantly smoked again. Reworked it. Looked hard at the wired connections in back and convinced myself that i had wired it up wrong. I have Red/blk going to the first port. Then Wht/red. Then two green wires and a black wire all going to the third port. Then 3 brown wires going to the last port. I fired it up and instantly smoked the speedo again. My questions. Is this wiring correct? Can anybody post a pic of a 1987 cab speedometer correct wiring? Second, without the speedometer in i ran the car and drove it a little. A cigarette lighter shows 13.8-14.1V pretty steady. What else might cause the resistor to smoke like this? Thanks in advance for the help. |
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09-09-2021, 12:44 PM
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Join Date: Feb 2012
Location: Hudson, NY
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Sorry, I couldn't resist.
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09-09-2021, 12:49 PM
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Can you post a picture of your wiring? The order of your wiring looks correct assuming the brown wires are on the ground terminal. You can tell it's the ground terminal because it's connected directly to the speedometer case and looks different than the other 3.
The only 2 wires that matter to diagnose the power issue are the ground (brown) and the positive (Red/Blk) which is on the opposite end of the connector. Assuming those are not swapped, the issue is likely with the driver board in the speedometer. There must be a short somewhere that is causing too much current through the resistor.
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1970 911E Sportomatic Albert Blue 1971 911T Sunroof Coupe w/ Twin Plug 2.5 MFI 1973 911E Glacier Blue 1973 911E RSR Tribute Viper Green w/ 3.5 Twin Plug MFI |
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09-09-2021, 07:45 PM
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Caveman Hammer Mechanic
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Check your alternator voltage.
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1984 Carrera El Chupacabra 1974 Toyota FJ40 Turbo Diesel "Easy, easy, this car is just the right amount of chitty" "America is all about speed. Hot,nasty, bad ass speed." Eleanor Roosevelt, 1936 |
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09-09-2021, 08:01 PM
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Is the voltage through the cigarette lighter voltmeter not the alternator voltage?
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09-13-2021, 02:38 PM
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Quote:
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1970 911E Sportomatic Albert Blue 1971 911T Sunroof Coupe w/ Twin Plug 2.5 MFI 1973 911E Glacier Blue 1973 911E RSR Tribute Viper Green w/ 3.5 Twin Plug MFI |
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09-13-2021, 02:43 PM
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So the voltage is about 14v steady. This should be ok. Attached are pic of the wiring. I realize the spade connectors are not all the way pushed in. Just attached it for the pics before I try turning it on again.
 
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09-13-2021, 03:10 PM
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14V is fine and your connections look OK. I suspect that there is a short on the board causing that resistor to keep frying. I'd be happy to take a look at it and let you know what it needs. Cheers
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1970 911E Sportomatic Albert Blue 1971 911T Sunroof Coupe w/ Twin Plug 2.5 MFI 1973 911E Glacier Blue 1973 911E RSR Tribute Viper Green w/ 3.5 Twin Plug MFI |
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09-13-2021, 03:18 PM
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Jbell959. What do you need to take a look at it? Picture of the board?
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09-13-2021, 05:02 PM
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Quote:
Sent from my SM-G991U using Tapatalk
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1970 911E Sportomatic Albert Blue 1971 911T Sunroof Coupe w/ Twin Plug 2.5 MFI 1973 911E Glacier Blue 1973 911E RSR Tribute Viper Green w/ 3.5 Twin Plug MFI |
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09-13-2021, 05:19 PM
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Waynec, John does great work. You can trust it coming out right. He rebuilt my 1985 speedo and tachometer.
Last edited by 911 SLANT; 09-13-2021 at 05:29 PM.. |
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09-13-2021, 05:25 PM
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Here are pictures of his work.
 
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09-13-2021, 05:28 PM
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