Horn Relay Retrofit for First-Gen 4Runners and Earlier Trucks

[RAD4Runner]

(Revised using different photo host because Google Photos Links Got Messed Up)

Why this mod?
Because my horn sounds like Mickey Mouse with his balls caught in a mouse trap - LOL!
Why?
Because the current for the first gen pickup and first gen 4Runner runs from battery, to horn, TO CABIN, TO HORN BUTTON ON STEERING WHEEL, back to engine compartment, to ground point on inner fender; No different from the convoluted path of headlight and starter relay current. This causes lots of voltage drops along the wiring and horn button, and subjects horn button to full load current; worse if one upgrades to higher power horn.

This mod will fix that, and allow us to put higher power horn(s) if we want.* I think this Horn Relay Retrofit will apply to all First-Gen and earlier which do not have horn relay. (I don't know about the 1989 pickup.)
Yes, I will still inspect/fix the sliding pin/contact in the steering column.

Second gen 4Runner has horn relay to carry horn load current:

HERE'S HOW I WIRED MINE:
Schematic explains most details.
IF you want to add an outrageously loud and powerful horn, I suggest you power pin 30 of relay with separate fused line from battery.

OVERVIEW AND GENERAL WORK AREA IS UNDER RIGHT -SIDE FENDER, FRONT CORNER (BELOW):

SNIP WIRES "A" AND "B" AT POINT WHERE IT WOULD BE EASY TO SPLICE / SOLDER.

SPLICE EXTENSION WIRES TO REACH RELAY IN ENGINE COMPARTMENT:
I put mine forward of the fuel injector resistor bank. Two feet of wire per extension worked well for me.

I LINED TOP SURFACE OF WHEEL-WELL WITH THIN RUBBER SHEET TO PROTECT WIRES.

I ALSO WRAPPED WIRE BUNDLE THROUGH THE GROMMET WITH SAME RUBBER SHEET FOR EXTRA PROTECTION.

I did not bother buying wires with stock colors so i just labeled new wires

ALSO ON YOTATECH HERE

 

[Dropzone]

As always [MENTION=80771]RAD4Runner[/MENTION] you write ups are awesome

 

[OzSurf]

Great write up! Definitely something I will need to do to my 1st Gen, my horn sounds exactly as you have described :rofl:

You mentioned the starter/headlights are wired in a similar fashion, is there a way to upgrade the stock wiring for these too? My headlights are terrible and my RPM's drop when I turn them on while idling, figure it probably wouldn't hurt to do some re-wiring.

 

[RAD4Runner]

Great write up! Definitely something I will need to do to my 1st Gen, my horn sounds exactly as you have described :rofl:

You mentioned the starter/headlights are wired in a similar fashion, is there a way to upgrade the stock wiring for these too? My headlights are terrible and my RPM's drop when I turn them on while idling, figure it probably wouldn't hurt to do some re-wiring.

Thanks, MateS!

Adding or Correcting Wiring of Starter Relay: http://www.toyota-4runner.org/class...d4runners-mods-restoration-7.html#post2182599


Re: Headlight
4Crawler, describes the problem here:
Brighter Head Lights

He also shows schematic of H4Relay Conversion Harness. You can buy one online or just make your own

I rewired mine by just adding a single relay here.
Difference in voltage drops (wasted energy) before and after are there.
In my case, even if the relay spots working, contact 87a stays closed, and I will still have my low-beam.

Idle dropping when headlights are turned on means either:
1) Weak alternator or battery,
2) Poor connection between battery positive and fuse block and fuses, (OR more likely)
3) Poor connection between Alt and fuse block (The Thick "B" wire on the alternator stud terminal).

H4 conversion harness will address 2 and 3 because headlight current will not go through the stock fuse block and cause voltage drop to engine control components.

 

[RAD4Runner]

Completed the Relay Retrofit
I updated original post abovehttp://www.toyota-4runner.org/classic-t4rs/258916-horn-relay-retrofit-first-gen-4runners-earlier-trucks.html#post3013746

I also have a wire running running to front left corner fender to an additional horn.

 

[Cali 4runner]

Love this idea! Been wanting to do it, just haven't gotten around to it. Nice write up!

Besides the horn, starter, and headlights I wonder what other wiring is inefficient on these rigs. I did notice when I step on the brakes at night the instruments lights dim a little. Plus the power windows cause the dome light to dim. Haha!

I need to spend more time looking at the diagrams.

 

[RAD4Runner]

... I did notice when I step on the brakes at night the instruments lights dim a little. Plus the power windows cause the dome light to dim.

Happens to mine, too. Also when blinker is on.
Probably because of all the cumulative resistance on every segment of wire going to each of these circuits.
Most we could do without replacing all splices and upsizing wires would be clean all screw terminals, and all connectors that could be unplugged that lead to all affected circuits.
Using LED bulbs would also help reduce load on circuits, especially the ones that use around 23 watts like blinkers, and brake lights. If using LED's for blinkers do not use the shunt resistors to make the work with stock blinker relay. They defeat the purpose of using LED's. Replace the blinker relay with one that works with LED's. or modify the stock one. (Someone has procedure for that on forum...)