Stop Lamp Failure
Racer
Joined: Sep 2015
Posts: 287
Likes: 4
From: Portland, OR
Reflowing the solder inside my 1986 lamp check unit made it work like new, if that turns out to be the issue. There's a fairly massive double induction coil on the circuit board that I suspect puts a lot of strain on the solder and causes tiny cracks. No idea how different the 1989 unit is though.
Rennlist Member
Joined: Jul 2006
Posts: 5,421
Likes: 627
From: Bloomfield, MI
My diagram for the 89 GT is too blurry to read on the stop light pin out the '90 states its pin 13 to the stop lamp bulbs. Going back and looking at the 89 diagram it looks like pin 13 too.
Power off, disco the lamp controller connector (pulls straight up).
Check pin 13 to ground (make sure it is not a direct ground and shows resistance with bulbs installed) w/o out bulbs it should show "open circuit".
Now take a 12v supply (fused, 5 amp?) now put +12v's to pin 13 of the connector (other end of power supply to ground) stop lamps should light, unless a wiring harness issue.
Pin 11 looks to go to the third(center) Brake light also.
Pin 7 is from the Stop lamp switch and you should see 12v there when the peddle is depressed (switch closed).
Is that what you see?
Like I said my drawing is not real clear, however if you use Fused 12v's and do some pre testing for grounds you should be able to power all the monitored lights via that connector.
Dave
Power off, disco the lamp controller connector (pulls straight up).
Check pin 13 to ground (make sure it is not a direct ground and shows resistance with bulbs installed) w/o out bulbs it should show "open circuit".
Now take a 12v supply (fused, 5 amp?) now put +12v's to pin 13 of the connector (other end of power supply to ground) stop lamps should light, unless a wiring harness issue.
Pin 11 looks to go to the third(center) Brake light also.
Pin 7 is from the Stop lamp switch and you should see 12v there when the peddle is depressed (switch closed).
Is that what you see?
Like I said my drawing is not real clear, however if you use Fused 12v's and do some pre testing for grounds you should be able to power all the monitored lights via that connector.
Dave
Racer
Joined: Feb 2014
Posts: 344
Likes: 10
From: Winston Salem, NC
This is not true, the lamp controller does power all the bulbs it monitors.
It does the "monitoring" by measuring the current flowing in each circuit and is "in-line". Unplug the Lamp controller and any bulb it monitors will not work.
It is actually a great place to start troubleshooting your issue.
You should be able to light up the Brake lights by supplying (fused) 12v's to the output of the Lamp controller's female connector that feeds the Brake lights.
The pins vary by model year as different bulbs were added to be monitored.
What year is your car?
Dave K
It does the "monitoring" by measuring the current flowing in each circuit and is "in-line". Unplug the Lamp controller and any bulb it monitors will not work.
It is actually a great place to start troubleshooting your issue.
You should be able to light up the Brake lights by supplying (fused) 12v's to the output of the Lamp controller's female connector that feeds the Brake lights.
The pins vary by model year as different bulbs were added to be monitored.
What year is your car?
Dave K
When I say "control" I'm thinking you get a signal then turn X output in. My thinking is the bulb control unit us only measuring voltage drop across a shunt resistor.
Rennlist Member
Joined: Jul 2006
Posts: 5,421
Likes: 627
From: Bloomfield, MI
Nope it is in series with the bulbs (like I already stated 
The connector (female) contains both Inputs (like from the stop lamp switch) and outputs to the various bulbs(lamps) like the Stop.
When I install LED's in the tail, Stop, Side marker, etc. I unplug the Lamp controller's connector and install Jumpers from the Inputs to the outputs, thus by-passing the Lamp controller completely.
So it is possible to have a bad Lamp controller which will cause an "open" or break in the corresponding lamp circuit.
Their is a write up that explains how it works and the resistors used to compare the current flow of the known good (standard stock) bulbs.
This is why it is important to use the correct Wattage and the same bulbs in each location.
Dave
The connector (female) contains both Inputs (like from the stop lamp switch) and outputs to the various bulbs(lamps) like the Stop.
When I install LED's in the tail, Stop, Side marker, etc. I unplug the Lamp controller's connector and install Jumpers from the Inputs to the outputs, thus by-passing the Lamp controller completely.
So it is possible to have a bad Lamp controller which will cause an "open" or break in the corresponding lamp circuit.
Their is a write up that explains how it works and the resistors used to compare the current flow of the known good (standard stock) bulbs.
This is why it is important to use the correct Wattage and the same bulbs in each location.
Dave
Thread Starter
Rennlist Member
Joined: May 2012
Posts: 1,128
Likes: 4
From: Ontario Canada
My diagram for the 89 GT is too blurry to read on the stop light pin out the '90 states its pin 13 to the stop lamp bulbs. Going back and looking at the 89 diagram it looks like pin 13 too.
Power off, disco the lamp controller connector (pulls straight up).
Check pin 13 to ground (make sure it is not a direct ground and shows resistance with bulbs installed) w/o out bulbs it should show "open circuit".
Now take a 12v supply (fused, 5 amp?) now put +12v's to pin 13 of the connector (other end of power supply to ground) stop lamps should light, unless a wiring harness issue.
Pin 11 looks to go to the third(center) Brake light also.
Pin 7 is from the Stop lamp switch and you should see 12v there when the peddle is depressed (switch closed).
Is that what you see?
Like I said my drawing is not real clear, however if you use Fused 12v's and do some pre testing for grounds you should be able to power all the monitored lights via that connector.
Dave
Power off, disco the lamp controller connector (pulls straight up).
Check pin 13 to ground (make sure it is not a direct ground and shows resistance with bulbs installed) w/o out bulbs it should show "open circuit".
Now take a 12v supply (fused, 5 amp?) now put +12v's to pin 13 of the connector (other end of power supply to ground) stop lamps should light, unless a wiring harness issue.
Pin 11 looks to go to the third(center) Brake light also.
Pin 7 is from the Stop lamp switch and you should see 12v there when the peddle is depressed (switch closed).
Is that what you see?
Like I said my drawing is not real clear, however if you use Fused 12v's and do some pre testing for grounds you should be able to power all the monitored lights via that connector.
Dave
