Pre 84 Trucks 1st gen pickups

GM Alt install problems

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Old 11-14-2012, 03:10 AM
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With the engine running, take your test meter and check if you have a steady voltage output and what the voltage output is the on "L", "F" and "P". Do not put 12 volt (Red Ignition Wire) power on "L". Let me know your results.
Old 11-14-2012, 03:28 PM
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Well I figured out what was wrong with my dash lights and tail lights. I didn't have the white wire that goes to the battery hooked up because I thought It came straight from the old alternator so I left it undone. After consulting my FSM I realized what I did lol.
Old 11-15-2012, 02:01 PM
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Also I think I may just leave the charge light circuit wired to switched 12V because without any power on it the thermostat/choke thing doesn't recieve power so the truck stays at high idle. This keeps the charge light off at all time but the dash brake light is still functional with the hand park brake.
Old 11-15-2012, 04:23 PM
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Alright suncomb1 I have idea and I want your opinion on it. In the old system did the voltage regulator send a signal to the alt to adjust voltage or did the adjusted voltage actually come out of the regulator and then to the system? I was thinking it was the 10/12 awg white wire from the alt that charged the battery and adjusted the voltage on this wire too. I'm thinking what If I put the old voltage regulator back in and connect the plug all except for whatever "output" that controls the voltage. Lets trick it into thinking its still working and that way it will control the charge circuit properly and eliminate the issues I have. What do you think?
Old 11-16-2012, 02:51 AM
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The Choke Heater Coil is supplied by the Yellow wire or "L" from the Toyota Voltaqge regulator. The Yellow wire / "L" also supplies power to to the Emissions Control Computer.
Did you perform the test on "L", "P" and "F" on the GM alternator? To get your Choke Heater Coil and Emission Control Computer working you could put a jumper from the Red Ignition wire to the Yellow wire in the harnes going into the cab; make sure the jumper wire is at least the same size as the Red Ignition or Yellow wire which ever is larger.

Last edited by suncomb1; 11-16-2012 at 03:09 AM.
Old 11-19-2012, 03:44 PM
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Originally Posted by suncomb1
With the engine running, take your test meter and check if you have a steady voltage output and what the voltage output is the on "L", "F" and "P". Do not put 12 volt (Red Ignition Wire) power on "L". Let me know your results.
No voltage on L,F, or P. Only wire hooked up was S during this test. Sorry for the delay, been busy with other stuff while it was warm this weekend.
Old 11-20-2012, 03:19 AM
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You need to check with the supplier of the GM alternator to find out if "L" should have voltage comming out of it. According to the wiring diagram you referenced, showing the indicator light circuit, the indicating light will not work unless there is voltage on "L". If the voltage has to be supplied to "L" via the ignition circuit then the resistor they show has to be installed. Let me know what you find out.
Old 11-20-2012, 05:11 AM
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Originally Posted by suncomb1
You need to check with the supplier of the GM alternator to find out if "L" should have voltage comming out of it. According to the wiring diagram you referenced, showing the indicator light circuit, the indicating light will not work unless there is voltage on "L". If the voltage has to be supplied to "L" via the ignition circuit then the resistor they show has to be installed. Let me know what you find out.
Power has to be supplied to L to excite the alternator so I guess I need to put that resistor somewhere.
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