Headlights flickering...

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

M

midwest

Full Access Member
Joined
Dec 28, 2021
Posts
188
Reaction score
202
Location
Indiana
First Name
Scott
Truck Year
1986
Truck Model
K20
Engine Size
350
First off, I probably know and understand less about wiring than anyone on this board, LOL... I replaced all 4 headlights in my K 20 (it started life as a 77 but has an 86 body on it.). The headlights had been in it for 15 years and a couple were burnt out. I just went with stock replacements from the local Oreileys. The first night driving it the lights started to flicker on an off, all of them. If I hit the high beams to switch to those they come on and it stops flickering for a few minutes. Then they start flickering again and if I switch from high to low or low to high it stops the flickering for a few minutes then the same thing. I had to do this for about a 10 minute drive home...
I didn't make any other changes, so I didn't know if a loose connection somewhere would cause this or somewhere else I should look.
 
R

Robert Bare

Full Access Member
Joined
Sep 13, 2020
Posts
107
Reaction score
176
Location
MT
First Name
Robert
Truck Year
1978
Truck Model
k20
Engine Size
5.7
Chances are your new bulbs are halogen, and drawing more current.
There is a circuit breaker built into the headlight switch, and chances are it is weak, and soon to fail. New switches are cheap.
BUT, you also could have a ground problem, or bad connections.
 
3 Ton

3 Ton

Member
Joined
Oct 14, 2024
Posts
39
Reaction score
70
Location
Pacific Northwet
First Name
Fred
Truck Year
1978-79 78 body, 79 gearing
Truck Model
K-15 Suburban
Engine Size
350
Switch is a good place to start, $20 at LMC, just got one. Im replacing all the switches.
The headlights have several connections from the light switch tot he bulb.
Bad grounding can cause this also.
 
AuroraGirl

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,693
Reaction score
6,875
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
whats a volt meter say at the battery, then at the headlight socket with the switch on ? low voltage means more current and these headlight systems are notorious for beeing WAYU too long on WAY too thin wires and also being 40+ years old

Get a relay harness regardless of what the fix is, youll have brighter headlights and youll stop pullinh the headlamp current through other things which causes voltage drop, dim lights, higher current, and wear
 
R

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
5,595
Reaction score
9,108
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
Robert Bare said:
Chances are your new bulbs are halogen, and drawing more current.
There is a circuit breaker built into the headlight switch, and chances are it is weak, and soon to fail. New switches are cheap.
BUT, you also could have a ground problem, or bad connections.
Click to expand...
This^^^ or a short in a headlight wire, which is tripping the breaker.And this is why GM uses a switch with a breaker,instead of fused headlights. With a fuse instead of low beam,flicker,off, highbeam, flicker, off, lowbeam is back,flicker,off. A fused head light circuit,is poof! You have no low beam instantly,poof you have no highbeam instantly. With the circuit breaker,slow blow flicker,you have time to slow down safely.
 
Last edited:
R

Robert Bare

Full Access Member
Joined
Sep 13, 2020
Posts
107
Reaction score
176
Location
MT
First Name
Robert
Truck Year
1978
Truck Model
k20
Engine Size
5.7
AuroraGirl said:
whats a volt meter say at the battery, then at the headlight socket with the switch on ? low voltage means more current and these headlight systems are notorious for beeing WAYU too long on WAY too thin wires and also being 40+ years old

Get a relay harness regardless of what the fix is, youll have brighter headlights and youll stop pullinh the headlamp current through other things which causes voltage drop, dim lights, higher current, and wear
Click to expand...
Ya, good points. 70's-80's Dodges were the kings of corrosion growing way up into harness wires, Chevy's undersized. Sometimes just adding driving lights could take out squarebody switches, and on the newer chevys burn up the headlight switches and connectors. I can't remember how many relays I have added to peoples vehicles, right at the headlights. Old yellow lights became almost white, halogens quit flickering, switches quit burning out.
 
M

midwest

Full Access Member
Joined
Dec 28, 2021
Posts
188
Reaction score
202
Location
Indiana
First Name
Scott
Truck Year
1986
Truck Model
K20
Engine Size
350
I am assuming the newer made switches are designed to handle the extra current drawn by the newer bulbs...
 
fast 99

fast 99

Full Access Member
Joined
Dec 31, 2021
Posts
2,090
Reaction score
3,065
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
midwest said:
I am assuming the newer made switches are designed to handle the extra current drawn by the newer bulbs...
Click to expand...
Not necessarily, changing original design could open up the manufacturer to unwanted liability such as an electrical fire. If higher amp draw is suspected run through a relay.
 
R

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
5,595
Reaction score
9,108
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
midwest said:
I am assuming the newer made switches are designed to handle the extra current drawn by the newer bulbs...
Click to expand...
No,most common would be just what was factory,maybe a little less with today's quality parts.But you couldn't up the amperage on the breaker in the switch unless people were also going to upgrade the wires otherwise wires would melt. As @fast 99 said relays would get more voltage to the headlights with less amperage through the switch. You could add relays and keep the old switch with relays the switch will see almost no load.
 
Last edited:
M

midwest

Full Access Member
Joined
Dec 28, 2021
Posts
188
Reaction score
202
Location
Indiana
First Name
Scott
Truck Year
1986
Truck Model
K20
Engine Size
350
Thanks, I'll still go ahead and try a new switch, then have one of my electrician buddy's help me with a relay.
 
R

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
5,595
Reaction score
9,108
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
midwest said:
Thanks, I'll still go ahead and try a new switch, then have one of my electrician buddy's help me with a relay.
Click to expand...
4 relays. 1 per headlight and function. Wired properly that way, a problem only results in the loss of 1 headlight not all 4 or even losing just high beams or low beams. Nbd in the driveway,a much bigger deal at 90 on the highway. Protect the circuit with breakers. Relay wiring #30 12 volt from battery. # 87 headlight power. #86 relay ground. #85 from old headlight power lead. For example, you turn on headlight low,the headlight low wire now triggers the relay,not the headlight. The relay closes and power flows from the battery to the headlight.
 
Last edited:
R

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
5,595
Reaction score
9,108
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
Before you do anything disconnect all headlights at the same time. Take a multi meter and check continuity to ground. Each headlight should have 1 wire with almost zero resistance to ground,all the other wires should show open if any of them get a reading other than open,I'd be looking for a short first.
 
Last edited:
You must log in or register to reply here.

Similar threads

C
Flickering headlights issue
Replies
4
Views
5K
Rickf
Rickf
Girth
LMC headlights/harness kinda wonky
Replies
2
Views
276
75gmck25
75gmck25
farmingwithJesus
86 C10 headlights went out
Replies
4
Views
878
farmingwithJesus
farmingwithJesus
D
Weird Headlight Problem
2
Replies
17
Views
900
Grit dog
Grit dog
J
Flickering headlights
Replies
2
Views
515
fast 99
fast 99

Latest posts

Forum statistics

Threads
44,411
Posts
956,918
Members
36,732
Latest member
blackmfcowboy
Top