I bought some Hella B133 horns. Assuming they will fit - do I need to use the relay included with them? I see in the service manual that the OEM horns are already triggered with a relay. If not - I should just be able to splice the wiring - correct?
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Horn replacement - need a relay if using electric horns?
- Thread starter hofffam
- Start date
On the early model years, the fuse that supplies the horns, brake light circuit and security indicator is rated at 20 amps. If your two horns draw anything close to 20 amps combined, you have a problem and should use the auxiliary relay. If the current draw of the new horns is only a couple of amps each, you are probably OK to eliminate the auxiliary relay.
A quick way to confirm this is remove the existing horn and measure the current flow when actuated by a 12 v source. Repeat with the Hella horn. If the Hella horn has similar or less current draw, you are good to go without the auxiliary relay.
A quick way to confirm this is remove the existing horn and measure the current flow when actuated by a 12 v source. Repeat with the Hella horn. If the Hella horn has similar or less current draw, you are good to go without the auxiliary relay.
shawn110975
Suspended
or plug one up and hit the horn if it works no more questions
if it doesn't and pops the fuse then you have your answer
if it doesn't and pops the fuse then you have your answer
I found a spec that says each horn draws 66 watts. That means 5.5A at 12V each or 11 A total at 12V. At 13.8V the draw is under 10A.
Seems like it might OK with existing wiring.
If I choose to use the relay, would you go straight to the battery or use an unused fuse terminal?
Seems like it might OK with existing wiring.
If I choose to use the relay, would you go straight to the battery or use an unused fuse terminal?
Unfused direct connections to the battery are bad news. Better to use an unused fuse position or if you connect directly to the battery, an in-line fuse holder.
The horns are probably not a constant load device. Probably more like a constant impedance device so as the voltage goes up the current to the device increases. If they are a pure constant impedance device, the current at 13.8 volts would be more like 12.6 amps. Probably OK; but, remember that the brake light circuit is supplied off of the same fuse. I haven't checked out the wiring diagram to determine what the current is associated with the brake light circuit.
The horns are probably not a constant load device. Probably more like a constant impedance device so as the voltage goes up the current to the device increases. If they are a pure constant impedance device, the current at 13.8 volts would be more like 12.6 amps. Probably OK; but, remember that the brake light circuit is supplied off of the same fuse. I haven't checked out the wiring diagram to determine what the current is associated with the brake light circuit.
Good advice on the fuse.
I didn't think about the impedance - that is something to think about. I suspect it probably does have a relatively constant impedance - perhaps like a loudspeaker. Hella says 65W per horn. It is a 12V device. P=IV so if P=65, V=12, then I must be 65/12 = about 5.4 A. Using P=(I**2)R then R might be 2.2 ohms. At 13.8V I might be 6.2A.
I ran three Hella horns in my 92 a while back. I skipped the relay and didn't have an issue. I haven't gotten around to putting them in my new(er) 2000.
I've been using the Hella B133 for years with no relay. Just put new terminals on the factory wiring and I've had no problems on my '93. I did need to make a mount that was a little longer.
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I do think you guys are actually using the original relay, just not the new one that comes with the kit. Do I understand this correctly? You replaced the actual horn and wired it to the original wires that feed the old horn, correct?
Regards,
LarryB
Yes, exactly Larry.
Correct
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