Hella headlamp upgrade problem w/fuse blowing
 

I upgraded the stock headlamps on my '73 450SL to Hella's 5 1/4" H4 (60/55 W) and H1 (55 W) lights, which the Mercedes part's dealer said were direct replacements. The 8 amp fuse won't take the load. The low beams work fine. However, activating the high beams blows the fuse. I know I've seen this topic discussed before, but I can't locate it. Any info on how to resolve would be appreciated.

8 amps. Are you sure thats the right size fuse. 55w @ 12V = 4.5 amps times 2 lights = 9 amps with the brights on thats 6 filliments going ~ 30 amps.

You will need to use relays. Use your 8 amp circuit to activate the relay and run higher fuesd power through the relays. Or just relay the highbeam circuit only, its probably safer that way.

John Roncallo

Fuse configuration
 

John, thanks for your reply. I see that you provide quite a bit of feedback to posters.

As to the configuration of the fuse box, the lights are designated right and left, and low beam and high beam. As such, there are four, 8-amp fuses for the lighting system. However, when the high beams are activated, according to your math there should be 9.6 amps at the high-beam fuse, which causes the fuse to blow. Do you believe that testing with a fuse rated at 10-12 amps should be attempted, and if that works put in a relay?

Yes you can test for a minute without a problem but I wouldent test for the night. Then just relay the second high beam circuit and put 8 amp inline fuses for the power line to the bulb. Use the wire that went to the bulb to energize the relay.

John Roncallo

What would the wiring diagram for the relays look like? I've been thinking of doing this upgrade to my 560 sl.

And if you don't mind, what relays do you use?

http://www.commandocaralarms.com/itemdetails.asp?ProductID=535

I dont have a wiring diagram, nor can I tell you which pins go where without one in my hand. You need a 4 or 5 pin relay. If you use a 5 pin you wont need to use the center pin. Generally the relays have a wiring diagram on them. The diadram will show that two of the pins are wired to a coil. Put one of these pines to ground and the other to the power that you would normally use to power the light when turned on. Now instead of turning on a high current draw light you will be actuating a switch using a low amount of current.

The other two pins are the heavy load carrying ones. One goes to the battery preferably with a fuse. A good place to pick up battery current in a 560SL is the large terminal block on the right inner fender wher the battery cable from the trunk terminates. The other wire goes to the light. Most of these relays are rated for 30 amps.

John Roncallo

The connector pin wiring between a sealed beam headlight unit and an H4 bulb is different. The connector fits mechanically but is wired differently. Most H4 kits come with a cross-over connector converter or at least a wiring diagram. Using it without changing the wiring for an H4 bulb will connect the low beam and high beam in series. This load will blow your fuses.

Problem Fixed
 

The fuse blowing problem was not fuse related. Poor pin connections caused the problem. I assumed that because the current light set worked that the connections were in good working condition. Upon inspection I found that when the car had been painted the pin connections to each bulb had been sprayed. I cleaned the connections, confirmed which lead to the high beam was the ground wire, reconnected the light set, and the lights worked fine. No relays or higher amp fuses were needed. Thanks to all of you who responded with helpful solution ideas.

Kelly