1. Home
  2. Mercedes Autos and SUVs
  3. Can horns be damaged by insufficient current?

Can horns be damaged by insufficient current?

When I bought my 1972 250C last week, the horns didn't work. The previous owner had replaced the stock horns with a set of Hella units, and he said that they had worked after he installed them. When I took the horns off and jumpered them directly to the battery, neither one would sound.

I replaced the Hellas with a pair of Fiamm horns, and they worked for about a day. Today, I honked the horns and they both cut out. Same problem as the others - I disconnected the horns and wired them directly to the battery to test them, and neither one worked.

The horn circuit is relatively simple. +12V from the hot side of the horn fuse is applied to terminal "A" of each horn, and terminal "B" of each horn is connected to a wire that is grounded through the steering wheel horn switch. The car, as well as all four horns it's killed, are twelve-volt, so it's not like I accidentally put in 6-volt horns or anything like that.

I'm thinking that the Fiamm and Hella horns may be drawing more current than the stock horns, and that they should have been wired with a relay connected directly to the battery, so that the stock horn wiring only has to activate the relay, and then the relay would provide power to the horns directly from the battery.

The only thing that puzzles me is that if the new horns are drawing too much current, I would have expected the horn fuse to blow, rather than the horns themselves dying.

Has anyone ever had a similar experience with aftermarket horns?

Thanks,

Reply to
Scott Gardner
Loading thread data ...

After you removed the "burn out" horns, did you check the voltage at the connectors terminals while actuating the steering wheel horn switch? It should be a healthy +12V

Reply to
Hernando Correa

With the horns removed, the voltage across the terminals was about

+12V. It wasn't exactly battery voltage, so there's a small loss in there somewhere, but not much.

I think the problem's solved now, though. I put in two new horns, but rather than use the original horn wiring to activate them, I wired them directly to the battery (via a fuse and a relay) and directly to a clean chassis ground. The original horn connectors now activate the relay, which completes the circuit from the battery to the positive horn terminals.

After I was done, I went to a deserted parking lot and tested the horn for about ten minutes. Now that they're getting full battery voltage, they're loud as hell, and the horn ring acutated them perfectly every time I pressed it. The horn switch will probably last longer too, since now it only has to pass enough current to activate the relay, instead of carrying all of the current for both horns.

The previous owner probably should have added a relay when he replaced the stock horns with the Hellas in the first place, but since he didn't, I should have done it the first time I replaced the Hellas with the new Fiamms. Serves me right for just re-using the existing wiring instead of figuring out the best solution.

Reply to
Scott Gardner

Wasn't there a relay to begin with and perhaps that was your whole issue?

Marty

Reply to
Martin Joseph

No, before I tore into the wiring, I checked with some other Benz owners, as well as examining the wiring diagram for the car, and there's no horn relay.

The stock wiring simply has a wire from the horn fuse to the positive terminals of the horns, and a second wire from the negative terminals of the horns that connects to ground via the horn switch in the steering wheel. The factory horns must not have drawn much current, because the factory wiring passes all of the horn current through the horn switch.

Reply to
Scott Gardner

Your adding the relay makes perfect sense since the current required to activate the relay is very small compared to the current needed to blow the horns. The side effect of your fix is that the steering wheel switch will outlast the life of the horns! These, however, will burn out if you were to test them CONTINUOUSLY for several minutes.

Reply to
Hernando Correa

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.