Need help on 3rd brakelight problem on a 90 vert.
Thread Starter
Intermediate
Joined: Aug 2001
Posts: 35
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From: Columbus NJ
Need help on 3rd brakelight problem on a 90 vert.
Forum members,
Failed NJ inspection last week due to the third brakelight being inoperative. The bulb & socket are good. Have 12 VDC at the base of the bulb and the ground is good. It appears to be an issue with the current being too low to operate the light. I believe this is a common failure, because I remember reading something here on the forum months ago. Any advise would be appreciated.
Regards,
Failed NJ inspection last week due to the third brakelight being inoperative. The bulb & socket are good. Have 12 VDC at the base of the bulb and the ground is good. It appears to be an issue with the current being too low to operate the light. I believe this is a common failure, because I remember reading something here on the forum months ago. Any advise would be appreciated.
Regards,
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: Need help on 3rd brakelight problem on a 90 vert. (Charcoal Grey 90)
If you have 12v on one wire on the brake light and the other wire is indeed ground, and the lamps are good, then they should light. I have had trouble with one socket that doesn't make good connection to the lamp pins. Try jumping 12v to the 12v wire and if no light, also jump the ground wire to ground, if no light, then the lamps are burned out or poor connection to the lamp pins from the socket pins. I am working on a LED replacement for the middle brake light and will announce it when finished.
Thread Starter
Intermediate
Joined: Aug 2001
Posts: 35
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From: Columbus NJ
Re: Need help on 3rd brakelight problem on a 90 vert. (jfb)
Yep! Tried that and the socket and bulb are good. I removed the socket from the vehicle and jumped it across a battery. I then hooked the voltage side of the bulb back to the vehicle and used an alternate ground. Still not working. I get about 11 or 12 volts at the base of the socket (measured with voltmeter), but it seems to be a bad connection, switch, ect due to lack of current. If someone has a service manual for the 1990 model or simular experiance, I'd like to know if this is a common problem. As I mentioned, I remember this topic being discussed in the past on this forum.
Thanks for your response,
:seeya
Thanks for your response,
:seeya
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: Need help on 3rd brakelight problem on a 90 vert. (Charcoal Grey 90)
If you plug a known good lamp (check with an ohmeter) into each socket one at a time (all other sockets empty), then with 12 volts applied, the lamp should light or there is no connection from the socket pins to the lamp pins. I would also check the circuit board that the sockets are soldered into. The board traces may have a hairline crack or the solder joints on the socket pins to the circuit board are defective. A high impedance voltmeter draws so little current that it will show 12v on the socket pins but the pins have enough resistance to not pass enough current to light the lamps. Your ohmeter should show essentially the same resistance as the lamp when you plug the lamp into each socket one at a time with your ohmeter across the wires to the circuit board.
Intermediate
Joined: Apr 2002
Posts: 30
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From: Palmer MA
Re: Need help on 3rd brakelight problem on a 90 vert. (Charcoal Grey 90)
I have an 87 coupe that failed the mass insp. for the same reason, I traced every wire in the car looking for the problem. I found the problem to be in the very expensive ABS relay box. I wired the third brake light directly to the brake light switch. It works fine, passed inspection, only comes on when I hit the brakes. I went in behind the light unit, cut the blue and the black wire, spliced in a new ground to body and ran a blue #14 wire in the wire harness to the brake light switch, Pulled the plug off the brake light switch and checked the pins with a volt meter to find the one the sends power to the brake lights when I make the switch, I installed a Y connector in the terminal and an insulated plug on the new wire and plugged it in. It cost me $4.00 and everything looks normal.
Thread Starter
Intermediate
Joined: Aug 2001
Posts: 35
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From: Columbus NJ
Re: Need help on 3rd brakelight problem on a 90 vert. (mrfix)
Wiring from the switch to the brakelight sounds like a good alternative. Can you advise where the ABS relay box is located? Also I was wondering if the wiring scheme is the same since the 1990 was the first year for the new dash. I have a service book for my 1992 which shows the a wire from the switch directly to the bulb (not routed through the ABS). If someone has a service manual, can you check and advise which is correct for the 90.
Thanks,
Thanks,
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: Need help on 3rd brakelight problem on a 90 vert. (Charcoal Grey 90)
Why would you want to wire from the switch to the brake light? The factory already did this and you measure 12v at the lamp socket which proves that the factory wire is ok. A new wire will do the exact same thing and the lamps will still not light. Your sockets must not be making contact with the lamp pins, otherwise the 12 volts you measure will make the lamps light up.
Intermediate
Joined: Apr 2002
Posts: 30
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From: Palmer MA
Re: Need help on 3rd brakelight problem on a 90 vert. (jfb)
The ABS stuff is behind the drivers seat below the storage compartment bottom, just pull it out, you will see the ABS valving and the relay box.
You can have 12 volts and not enough amperage to light the bulbs, I am assuming that the blocking diode for the brake light and the directional light wiring is faulty, when you wire directly to the switch, you are energizing the third brake light directly and not the rear brake lights, they are still powered normally. If you add an after market third light to and 86, that's how it's done. Trust me, I did it, it works.
You can have 12 volts and not enough amperage to light the bulbs, I am assuming that the blocking diode for the brake light and the directional light wiring is faulty, when you wire directly to the switch, you are energizing the third brake light directly and not the rear brake lights, they are still powered normally. If you add an after market third light to and 86, that's how it's done. Trust me, I did it, it works.
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