I just recieved my new Hella headlight/H4 conversions with 100 watt hi beams and 55 watt low beams and installed them last night. They seem to provide more-than-enough light on both hi/low but on high they seem to get awfully hot. I'm afraid that they might fry the wiring on my '85 SR5 Extra Cab. Have any of you used the 100 watt bulbs? And did you experience any heat related wiring problems. Any info will be appreciated. Thanks. Jerry
Yes, and yes - with the larger lamps, you are drawing almost double the current on high-beams, and the wiring on most new cars is just barely large enough for the stock lamps. You have to install a relay and heavier wiring to fed the high-beams - same 'cube' type used all over the car. Use the existing high-beam feed and ground to pull in the coil, and wire a fused line straight from the battery to the relay common, and the NO out to the high-beam terminal.
If you don't want to cut up the factory harness (I sure wouldn't!) you can buy "replacement" lamp sockets to plug onto the headlights, and .250 male blade crimp terminals to stick into the factory headlight sockets to pass through the low-beam power and ground (tap a local ground from the new socket to the chassis, too - the current is also doubled). And tap the high-beam power on one side to pull up the relay.
If all that sounded like Greek to you, go get help with this. A new main wiring harness replacement for most cars is well past $1,000.00, so you can see there's a healthy screw-up potential...
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I run the same setup in my '85, I bypassed the stock wiring for the lights, made a bigger improvement than the higher output bulbs:
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