Signal works, but brake light doesn't ?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Scrub · 02-09-2004, 01:52 AM

Both my rear signals work, but my left brake light doesn't come on? I know the same wire feeds the same filiment for both brakes and signals.
Is there some diode that might be toasted.

It's a 70 GMC 3/4 ton

Thanks in advance.

mshirey · 02-09-2004, 02:34 AM

There are two wires that feed the brake/tail lights and two filaments in the bulb. Since the tail lights are working I would say the ground is probably ok. Best guess would be a short either in the rear harness or in the intermediate harness that runs along the left frame rail.

cdowns · 02-09-2004, 03:02 AM

sounds like you need a new light bulb#1157

Longhorn Man · 02-09-2004, 08:11 AM

Looking liek a turn signal switch.
The parking light works off the brown wire. The brake light AND the left turn signal work off the green wire. (And the green wire only)
If the light lights up for thesignal, and not the brakes...then that proves that the wire and all connections are good south of the switch.
I can't see any way it can NOT be the turn signal switch.

JimKshortstep4x4 · 02-09-2004, 09:00 AM

I would have to agree with Longhorn. Try moving the turn signal lever while holding the brakes on to see if the lights will light up.

Jim

tom hand · 02-09-2004, 09:26 AM

Yep...turn signal switch. Try removing your steering wheel and cleaning the contacts before replaceing it....sometimes it's just dirt.

TsgtE662 · 02-09-2004, 11:58 AM

I'd change the bulb first. Its easier and cheaper.

Blue Beard · 02-09-2004, 12:36 PM

If only the left brake light isn't working, sounds like it would be towards the back.

Generally speaking the yellow and green wires are turn signal, and the brown is running lights.

Longhorn Man · 02-09-2004, 05:53 PM

Some of you are not realizing that the brake light folows the exact same wire as the turn signal.
So if his turn signal works, then the bulb is good, as is the wires going all the way back to the tail light.

tom hand · 02-09-2004, 08:57 PM

Quote:

Originally posted by Longhorn Man
the brake light folows the exact same wire as the turn signal.
.

The brake light IS the turn signal in the back. When you put on your blinker, it flashes the BRAKE light. So with the problem described above, the problem is going to be in the switch. I had the same problem after I painted my truck, because I had gotten some paint into the switch. Removed the steering wheel, cleaned the contacts, and it works like new.

Scrub · 02-10-2004, 01:06 AM

Thanks to all.
The old girl has over a million miles and still goes great. I guess it's time to clean up the turn signals again.

Longhorn Man · 02-10-2004, 01:48 AM

I knew some one on here had me beat in the mile department....I just couldn't remember who.

02-09-2004, 02:34 AM	#2
mshirey Registered User Join Date: Apr 2000 Location: San Diego, CA Posts: 110	There are two wires that feed the brake/tail lights and two filaments in the bulb. Since the tail lights are working I would say the ground is probably ok. Best guess would be a short either in the rear harness or in the intermediate harness that runs along the left frame rail. __________________ Mike 67' GMC Fleetside

02-09-2004, 03:02 AM	#3
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	sounds like you need a new light bulb#1157 __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

02-09-2004, 09:26 AM	#6
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Yep...turn signal switch. Try removing your steering wheel and cleaning the contacts before replaceing it....sometimes it's just dirt. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

02-09-2004, 11:58 AM	#7
TsgtE662 2A674 Tank Rat Join Date: Jul 2003 Location: Maryland Heights, Mo. Posts: 625	I'd change the bulb first. Its easier and cheaper. __________________ '92 GMC Sierra, Sportside, 2wd, 350, Black '92 Chevy Silverado Extended Cab 4 x 4, Blue USAFR = 2A674 = Aircraft Fuel Systems Maintenance i.e. Tank Rat

02-09-2004, 12:36 PM	#8
Blue Beard Registered User Join Date: Jan 2003 Location: Washington State Posts: 8,831	If only the left brake light isn't working, sounds like it would be towards the back. Generally speaking the yellow and green wires are turn signal, and the brown is running lights. __________________ 1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00 1978 Silverado 2005 Monte Carlo

02-09-2004, 01:52 AM	#1
Scrub Collector of rusty Items Join Date: Dec 2001 Location: Sisters,Oregon USA Posts: 731	Signal works, but brake light doesn't ?? Both my rear signals work, but my left brake light doesn't come on? I know the same wire feeds the same filiment for both brakes and signals. Is there some diode that might be toasted. It's a 70 GMC 3/4 ton Thanks in advance. __________________ Scrub Sisters, Oregon - Home of the Sisters Rodeo. 70 GMC 1,000,000 + miles 72 K-20 project, 456 Dana60 front, Corp14 rear w/locker, 265R19.5 tires 20-ply. Warn 12k winches both ends, Cross-over steering with raised tie-rod, Powerbox steering, 4500 watt 120-AC power, Air, Hydraulic aux power, 4 inch lift, 5000 lb air-bags both ends.

02-09-2004, 08:11 AM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Looking liek a turn signal switch. The parking light works off the brown wire. The brake light AND the left turn signal work off the green wire. (And the green wire only) If the light lights up for thesignal, and not the brakes...then that proves that the wire and all connections are good south of the switch. I can't see any way it can NOT be the turn signal switch.

02-09-2004, 09:00 AM	#5
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	I would have to agree with Longhorn. Try moving the turn signal lever while holding the brakes on to see if the lights will light up. Jim

02-09-2004, 05:53 PM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Some of you are not realizing that the brake light folows the exact same wire as the turn signal. So if his turn signal works, then the bulb is good, as is the wires going all the way back to the tail light.

02-10-2004, 01:06 AM	#11
Scrub Collector of rusty Items Join Date: Dec 2001 Location: Sisters,Oregon USA Posts: 731	Thanks to all. The old girl has over a million miles and still goes great. I guess it's time to clean up the turn signals again. __________________ Scrub Sisters, Oregon - Home of the Sisters Rodeo. 70 GMC 1,000,000 + miles 72 K-20 project, 456 Dana60 front, Corp14 rear w/locker, 265R19.5 tires 20-ply. Warn 12k winches both ends, Cross-over steering with raised tie-rod, Powerbox steering, 4500 watt 120-AC power, Air, Hydraulic aux power, 4 inch lift, 5000 lb air-bags both ends.

02-10-2004, 01:48 AM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	I knew some one on here had me beat in the mile department....I just couldn't remember who.

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