Changed Alternator Now No Headlights ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

54blackhornet · 12-15-2018, 03:45 PM

The bearings in the alternator on my 71 C20 where getting noisy so I swapped in one I had on the shelf. Now I have no headlights, any thoughts...

Andy4639 · 12-15-2018, 05:25 PM

You left a wire off.

Changing the alternator shouldn't effect the lights. Look and see if you blew a fuse. Do you have any power at all?

mr48chev · 12-15-2018, 05:52 PM

I'd go with left a wire off but first take your test light and check both sides of the headlight fuse. You should have power to the fuse all the time and if you don't have power to the fuse start backtracking on the power feed.

Check any connection you took loose when and before you pulled the old alternator off to see if you left something off.

Looks for non factory wires that may have been installed to bypass a suspect circuit and feed power to the lights that you may not have reconnected. Half of these trucks have an extra wire on them to run power to something because of bad connection that wasn't fixed to be the way it was designed.

54blackhornet · 12-16-2018, 05:21 PM

Thanks guys ! Funny not many wires behind the alternator ? I do have marker and dash lights. I’ll start tracing wires....

Andy4639 · 12-16-2018, 10:00 PM

Dimmer switch!!!!

Shinysideup · 12-16-2018, 10:37 PM

Quote:

Originally Posted by Andy4639

Dimmer switch!!!!

Beat me to it!

68 P.O.S. · 12-16-2018, 10:42 PM

x3 on the dimmer switch

rockyrivermark · 12-17-2018, 05:06 PM

take a light 12v tester and see if you have power at the headlight socket with switch on. use body ground on tester and not the ground at socket.
could have knocked a ground off somehow.
if no power, see if power comes out of switch for headlights.

Andy4639 · 12-18-2018, 08:16 AM

Power comes out of head light switch to dimmer switch in the floor. The dimmer splits the power to the low side and high side. Check the dimmer first thing.

12-15-2018, 03:45 PM	#1
54blackhornet Registered User Join Date: Jul 2008 Location: Eastern Oregon Posts: 2,251	Changed Alternator Now No Headlights ? The bearings in the alternator on my 71 C20 where getting noisy so I swapped in one I had on the shelf. Now I have no headlights, any thoughts... __________________ 71 C-20 07 Magnum RT AWD

12-15-2018, 05:25 PM	#2
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Changed Alternator Now No Headlights ? You left a wire off. Changing the alternator shouldn't effect the lights. Look and see if you blew a fuse. Do you have any power at all? __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

12-15-2018, 05:52 PM	#3
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,268	Re: Changed Alternator Now No Headlights ? I'd go with left a wire off but first take your test light and check both sides of the headlight fuse. You should have power to the fuse all the time and if you don't have power to the fuse start backtracking on the power feed. Check any connection you took loose when and before you pulled the old alternator off to see if you left something off. Looks for non factory wires that may have been installed to bypass a suspect circuit and feed power to the lights that you may not have reconnected. Half of these trucks have an extra wire on them to run power to something because of bad connection that wasn't fixed to be the way it was designed. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

12-16-2018, 05:21 PM	#4
54blackhornet Registered User Join Date: Jul 2008 Location: Eastern Oregon Posts: 2,251	Re: Changed Alternator Now No Headlights ? Thanks guys ! Funny not many wires behind the alternator ? I do have marker and dash lights. I’ll start tracing wires.... __________________ 71 C-20 07 Magnum RT AWD

12-16-2018, 10:00 PM	#5
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Changed Alternator Now No Headlights ? Dimmer switch!!!! __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

12-16-2018, 10:42 PM	#7
68 P.O.S. Registered User Join Date: Jan 2007 Location: Puyallup, WA Posts: 1,661	Re: Changed Alternator Now No Headlights ? x3 on the dimmer switch __________________ 72 C10 lwb fleetside -stock 350/350 combo

12-17-2018, 05:06 PM	#8
rockyrivermark Registered User Join Date: Apr 2011 Location: Fairview Park, Ohio Posts: 1,027	Re: Changed Alternator Now No Headlights ? take a light 12v tester and see if you have power at the headlight socket with switch on. use body ground on tester and not the ground at socket. could have knocked a ground off somehow. if no power, see if power comes out of switch for headlights. __________________ My build page http://67-72chevytrucks.com/vboard/s...d.php?t=764662 My cabinet building site http://www.cbcabinets.com Last edited by rockyrivermark; 12-17-2018 at 05:16 PM.

12-18-2018, 08:16 AM	#9
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Changed Alternator Now No Headlights ? Power comes out of head light switch to dimmer switch in the floor. The dimmer splits the power to the low side and high side. Check the dimmer first thing. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.



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