Relays for headlights (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

TEXASgirl

TEXASgirl

Joined
Nov 23, 2009
Threads
20
Messages
75
Location
Dallas, TX
The quick version: What relay is needed to run the headlights?


So we've got the "no headlights" issue narrowed down to a 4 post power relay (12volt 30 Amp). We ran a "cheater wire" from the light switch (by-passed the relay) and ran directly into the headlight...left all other wires hooked up to the relay and the lights worked fine (low beam only).

Any ideas?
Does it require a single throw or double throw relay?

Thanks,

J & B
 
I just used two relays.
One for lowbeam, one for high. Cheap, simple, and if one relay breaks then i'll at least have one setting.

attachment.php

pic taken from https://forum.ih8mud.com/40-55-series-tech/49007-h4-relay-headlight-upgrade-diagram.html
 
Last edited:
Summit sells a headlight relay kit for about $25 bucks. I bought it but ended up not using it w/ my painless wiring harness. Seemed like a pretty good kit for both high and low beams.

Nick
 
I've bought brand name headlight relays from the big rig shops (Western Star Lines) for $3or4.

Those trucks are worked hard day and night.
:)
 
That diagram is GREAT. Looks like our problem might not be a bad relay but mixed up wiring by the PO. Looks like more chasing down wires...for my husband. Haha!

Thanks for the feedback guys. Any additional recomendations on where to locate affordable relays. All the parts stores want $20 and up for them!
 
I don't like that diagram.

It would be much cleaner to ground the switch to activate the relays.
 
psreno said:
I don't like that diagram.

It would be much cleaner to ground the switch to activate the relays.
Click to expand...

I politely disagree. The headlight switch is simply a low current pass through to allow the high/low switch (combo or dimmer) to control the appropriate relay. The relays handle the high draw headlights. No need for the headlight switch to be a relay as there isn't a lot of voltage passing through it.

I need to put some relays into my off-road light circuits to get all that amperage out of the cab.:hillbilly:
 
I bought the painless headlight relay kit from summit and saw a noticeable increase in brightness on both the low and high beams.
 
You can politely disagree all you want, but you are going to be running a lot more wire.

Would it help you if I said "ground the switch TO THE RELAY to activate the LIGHTS". I'm not talking about abandoning the relays, just how they are wired is inefficient.

Your method will still have 12V coming through the cab when the lights are OFF. I don't like that and it doubles the amount of wire needed (hence higher resistance and current).
 
psreno said:
I don't like that diagram.

It would be much cleaner to ground the switch to activate the relays.
Click to expand...

Any chance you could draw a diagram? I would like to see that. It IS a lot of wiring.
 
IDave said:
Any chance you could draw a diagram? I would like to see that. It IS a lot of wiring.
Click to expand...

yeah, I'd be interested in seeing that wiring too. I understand it conceptually, but I am still a :banana: newb.

Thanks.. :flipoff2:
 
For cheap relays:

Head to a pick-n-pull junkyard and look under the hood of about any newer vehicle. Another poster suggested a heavy truck repair shop (usually found at the bigger truck stops).

Wiring thoughts:

I bought a truck that used a IPF headlight relay kit. It plugged into the existing headlight harness (as in you removed both plugs from the back of the headlights and plugged one of those into the IPF harness). No extra wiring back into the cab; you just used the stock wiring. The IPF harness pulled juice from the battery directly (with a fuse on the hot side like the wiring diagram already posted) to power the headlights with their own plugs.

Nick


TEXASgirl said:
That diagram is GREAT. Looks like our problem might not be a bad relay but mixed up wiring by the PO. Looks like more chasing down wires...for my husband. Haha!

Thanks for the feedback guys. Any additional recomendations on where to locate affordable relays. All the parts stores want $20 and up for them!
Click to expand...
 
Basically you run the power from source to relay. Split it there and jumper the 12V to one of the switched leads on the relay. Then run a wire from the other switch lead to the switch, and from the switch to ground (usually where it's mounted). Yes, it will still have live 12V into the cab, but when you activate the switch to ground it energized the relay coil and waalaa, power to the load comes off the relay. This way it is also all coming off of one fuse (you can add more, smaller fuse inline the switch if you want).
 
FWIW, Radio Shack will sell the relays (Bosch most likely) and they aren't cheap. However Radio Shack will not sell the pigtail adapter. You will need to go to Sandy's or like electronics store.

Salvage yards have oodles, cheap, inside most doors and some trunks for the window/lock operations.
 
psreno said:
You can politely disagree all you want, but you are going to be running a lot more wire.

Would it help you if I said "ground the switch TO THE RELAY to activate the LIGHTS". I'm not talking about abandoning the relays, just how they are wired is inefficient.
Click to expand...

Hmmm. In the diagram the switch is grounded through the relay. Not a lot less wire to run two wires backward from your jumpers through two fuses (advisable) to the combo/dimmer and then a single wire to the switch and then to ground. The diagram doesn't show the OEM fuse box location but it's presumed to be at the firewall thus the change in wiring color at that point. The only wire I can see that gets eliminated is the bat thru firewall to switch. I guess you'd simply cut that one (or pull the fuse) if you're still running a factory wiring harness. Sorry for being so dim.

psreno said:
Your method will still have 12V coming through the cab when the lights are OFF. I don't like that and it doubles the amount of wire needed (hence higher resistance and current).
Click to expand...

Yes, the wire to the switch (in the diagram) is hot but there is no draw when the lights are off and can now be fused with as little as 5 amps - maybe less. No more dangerous than the radio circuit. Are there any OEMs that wire switches your way? I'm only used to seeing the equivalent of the H4 diagram but I have limited experience.

NOTE: The junkyard is a great place to get relays but there are multiple versions that, for all intensive purposes, appear the same. Some switch current and some shut it off, etc, etc. Sorry, I don't remember the Bosch part numbers.
 
relays are pretty cheap, maybe $3-$5 at an auto-parts store or Radioshack, and even cheaper if you have a cruiser buddy that is an EE. You can do this for less than $20. These vehicles are fairly old, and you might as well replace the wiring now. This only took maybe 20min to wire up after soldering/crimping and running wires. Very noticeable increase in light output. Before this upgrade i was only getting 9volts to the headlights in the old/stock config.
 
For the 2 switch wires you can run speaker wire instead of 2 individual strands. I don't think you have to go with monster cable, but I wouldn't use the real skinny stuff just because any corrosion at all will eat right through.

Here's a good relay resource, the relays here are $2.90:
Hella Relays & Connectors - Waytek, Inc.  - Waytek Wire

I'm bummed that I can't find the link to a relay diagram generator that I've used quite often (I am an EE after all). It has 3 pull down filters and pulls up the diagram for whatever you want to do such as running a reversible motor or locking latches. I'll post it if I can find it.

Numby, switch is a switch, so when I wire in a steering column it does whatever I wire it to. I'm sorry if I'm being cavalier - I didn't take the diagram as anything but a general idea, not a vehicle specific diagram. You are correct in that some relays haven't all their terminals. Usually a relay will have a normal open as well as a normal closed terminal. In mass they save some cents without the extra terminal.
 
You must log in or register to reply here.

Similar threads

yomumsbum
79 fj45 headlights help please
Replies
14
Views
1K
45Dougal
45Dougal
69FJ40NJ
Headlights and parking/turn signal lights issue
Replies
8
Views
684
45Dougal
45Dougal
newlandcruiserguy
Headlights not working + 4Plus bumper and winch!
Replies
4
Views
735
Strait Cruisin
Strait Cruisin
Kschep
Headlight juice
Replies
18
Views
1K
Kschep
Kschep

Users who are viewing this thread

Total: 2 (members: 0, guests: 2)

Share this page

Back
Top Bottom