Bungled horn install, eating fuses.

[CrankyOldMan]

So my horn install had been working swimmingly, but the shortcut I took with the relay has gone all wrong. I mounted the relay where the horn is installed to make the wiring simpler and wrapped the junction in electrical tape. Well, at some point this winter, the salt and moisture seeped into the relay and corroded all of the contacts together. I went this way with it because I'm using two FIAMM freeway blasters in parallel and had to run a larger gauge wire to the horns.

My first remedy was to change the 10A horn fuse in the engine bay fuse box: turn on car, no honk, burned up the fuse. No worries, there was a spare relay handy: connect relay, replace fuse, turn on car, no honk, burned up the new fuse. The relay was also warm. Strange.

The next step was to try the horns individually with an inline fuse direct from the battery. One horn worked, the other didn't. Time for a continuity test. The DMM showed them as having similar resistances of around 3.4 ohms, so that has me a bit stumped.

Ok, time to get out the repair manual. The diagnostics for the integrated relay box involve hooking some very small pins up to a power supply and DMM. I'm really not sure how to safely clip on to those without a sacrificial dongle, and a replacement is at least $50-60 even from a junk yard.

Anyone have any suggestions of how to proceed from here?

[CTScott]

Disconnect everything beyond the OEM wiring, and verify that you see 12V on the green wire in the under hood fuse box that feeds the OEM horn (you don't need to reconnect the OEM horn, you are simply looking to see that the horn switch feeds the horn relay and that the horn relay contacts close, feeding 12 V to that wire). See the link below from when I installed my horns for details on that wire:

http://www.yarisworld.com/forums/sho...4&postcount=22

[Betrivent]

if it helps, I installed hella's this weekend, and all I did was wire the positives together and then to the car's single OEM wire. Then I grounded them to the metal bracket the horns are mounted it. Works like a charm.

[TOLMACH]

^ Same with me.. no relay was used

[Yaristeve]

Originally Posted by CrankyOldMan

Well, at some point this winter, the salt and moisture seeped into the relay and corroded all of the contacts together. I went this way with it because I'm using two FIAMM freeway blasters in parallel and had to run a larger gauge wire to the horns.

My first remedy was to change the 10A horn fuse in the engine bay fuse box: turn on car, no honk, burned up the fuse. No worries, there was a spare relay handy: connect relay, replace fuse, turn on car, no honk, burned up the new fuse. The relay was also warm. Strange.

Not so strange. It's probably safe to assume that your relay is shorting directly to ground so it needs to be replaced. There should only be milliamps of current through the switch side, not nearly enough to pop a 10A fuse.

Originally Posted by CrankyOldMan

The next step was to try the horns individually with an inline fuse direct from the battery. One horn worked, the other didn't. Time for a continuity test. The DMM showed them as having similar resistances of around 3.4 ohms, so that has me a bit stumped.

It could be the electical circuit is fine (the electromagnetic coil) but the diaphragm is corroded and stuck, thus resistance will measure the same but no sound.

Best (easiest) solution is to buy the Toyota OEM "Premium horn" kit:

http://www.ebay.com/itm/TRD-LEXUS-19...49d22d&vxp=mtr

It is totally plug-n-play including the Y-connector. I bought a set for my Yaris a couple of years ago and love it (but prices have gone waaaaayyy up. I think I paid about $70)...

Otherwise, replace the individual components (relay, one horn) and you should be good (make sure to buy a good relay and install it somewhere where it is protected).

[mazilla]

You can better waterproof your next relay by wiring it, holding it by the leads and then dipping the whole thing in plastidip or brishing on layers of liquid electric tape. Just keep track of which wire is which...once it's dipped you obviously won't be able to read it anymore.

[CrankyOldMan]

Thanks for all the replies! I think this time I'm going to put the relay somewhere safer, like the way CTScott did his.

As far as the Hella vs FIAMM relay business, the Hella's are rated at 10A or less, so they can directly replace the single OEM horn. The FIAMMs draw more than 5A each (8, iirc) so they require a separate switched line from the battery to keep from damaging the stock horn wire.

[jcboy]

the reason why you keep breaking fuses is that the relay's feed in 85 (from the stock wiring's +12V) is now shorted to 86 (ground) (or vice versa, whichever way you did it).

change your relay, and yes, weatherproof it, and youre good to go.

here's the connections as a refresher:
stock wiring +12V --> relay 85
battery +12V --> relay 30
horn +12V --> relay 87
horn (-) and relay 86 --> body ground

if you want you can insert an inline fuse from battery +12V to relay 30, your best bet is somewhere closer to the battery than to the relay.

makes sense?

[TOLMACH]

Originally Posted by jcboy

the reason why you keep breaking fuses is that the relay's feed in 85 (from the stock wiring's +12V) is now shorted to 86 (ground) (or vice versa, whichever way you did it).

change your relay, and yes, weatherproof it, and youre good to go.

here's the connections as a refresher:
stock wiring +12V --> relay 85
battery +12V --> relay 30
horn +12V --> relay 87
horn (-) and relay 86 --> body ground

if you want you can insert an inline fuse from battery +12V to relay 30, your best bet is somewhere closer to the battery than to the relay.

makes sense?

^ This is nice.. will save for myself - needed ignition controlled power for my gauges recently (now fed through cigarette lighter.. will change now)

[CrankyOldMan]

Originally Posted by jcboy

the reason why you keep breaking fuses is that the relay's feed in 85 (from the stock wiring's +12V) is now shorted to 86 (ground) (or vice versa, whichever way you did it).

change your relay, and yes, weatherproof it, and youre good to go.

here's the connections as a refresher:
stock wiring +12V --> relay 85
battery +12V --> relay 30
horn +12V --> relay 87
horn (-) and relay 86 --> body ground

if you want you can insert an inline fuse from battery +12V to relay 30, your best bet is somewhere closer to the battery than to the relay.

makes sense?

Yep, that's how it was wired. I just made the mistake of thinking that a few wraps with electrical tape would be sufficient to protect the relay. I was also lazy and put the fuse next to the relay, but that one didn't blow (I think).

[jcboy]

Originally Posted by CrankyOldMan

Yep, that's how it was wired. I just made the mistake of thinking that a few wraps with electrical tape would be sufficient to protect the relay. I was also lazy and put the fuse next to the relay, but that one didn't blow (I think).

haha yeah i had exactly all the same mistakes with my previous car's horn wiring. i also kept destroying relays (about 4 times) and sometimes blowing the stock fuse because of that (twice), and never for once did my inline fuse blow. (that inline fuse was near the battery, before the wire to relay 30 terminal). too lazy to rewire the relay to the engine bay and not behind the front bumper.

and yeah, if your relay gets busted inside, it can either give an open circuit (safe), or a closed circuit (shorted, not safe) and blow up your stock fuse (where the +12V {that goes to relay 85} is wired from).

[jcboy]

Originally Posted by TOLMACH

^ This is nice.. will save for myself - needed ignition controlled power for my gauges recently (now fed through cigarette lighter.. will change now)

you can still use the cigarette lighter as feed for terminal 85 of the relay.

1. relay 85 from cig lighter +12V
2. relay 86 from cig lighter ground (black wire, if it exists), else, short it with gauge's (-)wire (connected to ground)
3. relay 30 from batt +12V (but put an inline fuse of 5A, depending on current rating of your gauges)
4. relay 87 to gauge's (+)wire
5. gauge's (-)wire to ground.

HTH

[TOLMACH]

^ Thanks