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Discussion Starter · #1 ·
I have an L67 in a Fiero and I'm using a 95 Bonneville ECM. I installed a Proform shift light and all was well until I decided to change over to a VDO tachometer. In order to get the VDO tach to work off of the Bonne ECM a friend of mine whipped up a little circuit( seems the VDO needs a 12v p-p signal and the ECM gives a 5V p-p signal). The circuit is an npn transistor with the ECM signal going thru a 470 ohm resistor to the base. 12V thru a 1000 ohm resistor to both the tach imput and the collector and the emitter to ground. The circuit makes the tach work great but now my shift light won't work (light input is tapped into the white wire from the ECM before it hits the circuit). If I disconnect the tach the light works. I have talked to both Proform and VDO - Profrom has no clue and VDO is "working on it". Any ECM/ Electronic gurus on here have any ideas.
 

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If you post the manuals and/or the schematic I'd be glad to help (I'm a EE) Just give me some time once you post the links to the manuals...
 

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My first thought since it will take me a while to find specs on these parts and your ECM, is that the shift light is getting the right voltage, but is not beind supplied enough current to turn on, thus when you unhook all this jazz the load is reduced and you can turn the light on. So, if you can find out the required current needed to turn the light on (or the draw of the light depending on how they phrase it) and go out there and measure what you are supplying it. My bet would be it's not enough, or in fact it may not be enough voltage.

Most likely if it was enough current but not enough voltage it would be dim but it would still be on. In your case there will prolly be enough voltage since its parallel with the ECM, but not enough current to turn it 'on'.

Let me know and I will still try and figure all this out for you. Other than that tell your friend this was a very good idea, I like it!
 

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Maybe adding a relay in there to supply the power needed for the shift light may help. Connect the trigger wire to the input of the relay, add a ground and power wire and the connect the light to the output of the relay. If it needs 12v then this will give it 12v and I think around 25 to 30 amps.
 

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I'm with the other two on this. Use a relay for the shift light.

I'm looking at the colors for a standard Bosch relay. Hook up the signal from the ECM to the white wire '85' on the relay. Then the black/yellow wires '86/87' are hooked up to a 12v constant. The blue wire '30' is the output to the shift light. '87a' is not used.

Someone pelase correct me if I'm wrong, but I believe this is how it's setup.
 

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Abysalone said:
Maybe adding a relay in there to supply the power needed for the shift light may help. Connect the trigger wire to the input of the relay, add a ground and power wire and the connect the light to the output of the relay. If it needs 12v then this will give it 12v and I think around 25 to 30 amps.

*edited to think*

Also, the relay is rated up to 30amps, it won't put out that much. It'll only put out as much as the wire you're hooking it up to allows (the wire that post 86 hooks to).
 

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Discussion Starter · #10 ·
I don't believe that a relay is the way to go - the ECM puts a 5V p-p puls signal to the shift light and the electronics inside the light light the light and a certian frequency. I'm afraid that a relay would be "fluttering" like a bandit and most likely couldn't cycle fast enough to work plus it would burn out in a very short time . But thanks for the thoughts. The light flashes when I first turn the key like it should but it just won't light at the set RPM
 

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Phil, question, what are all of the wires that are need to hook up the tach and shift light, and what do they need? Please list all components that come with the shift light/tach assembly as well.

the tach should need a 12v ign, a ground, and a tach input. The shift light from what I can think of, would need a 12v ign (possibly), ground, and tach input. Right? Also, I'll assume "P-P" means positive-pulse?
 

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ChaosStarter said:
Abys, if say you had a (-) trigger parking lights, and a negative output from an alarm, then you would hook it up the way you said. In your case, hooking up the black (86) to 12v and yellow (87) to ground, and used white (85) as your input and blue (30) as your output, then that would make the output a (-) trigger.

Also, the relay is rated up to 30amps, it won't put out that much. It'll only put out as much as the wire you're hooking it up to allows (the wire that post 86 hooks to).
Im probably wrong here but I think in order to make it a negative trigger you would need to ground the positive on the relay and add power to the negative side. Dont take my word for it though. Go to an alarm companys home page and look through their manuals or do a search online about bosch relay's.
Phil, I think your right about the fluttering effect. Sorry I cant help you more.
 

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actually, the info i posted was dumb of me cause i didn't realize what i was actually typing.

if you have a negative output from the brain, and a negative trigger (12v normally shows) then you wouldn't need a relay as the negative pulse would do the job. you only need relays to change a negative trigger to a postive (or vice-versa) or to amplify a positive output moreso. also, there are no real postive or negative sides on a relay, just a bunch of inputs and outputs.

i'm going to try to figure out this setup for wtf i was trying to talk about before. :confused:

phil - why did he use a 1k ohm resistor for the 12v signal to the VDO? also, found this on 12volt.com:

Pulsed to Steady Output
If you have cornering lights and want them to come on only when your turn signal is on and you do not have a steady output, use the following for each side. This will give you a steady output while the turn signal is on. Increasing the size of the capacitor will give you a longer output if needed.
 
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