The PO of my 86 4Runner had already done a H4 headlight conversion prior to my purchase. Appeared to be a cheap kit, likely from ebay. The housings went bad (leaked, rusted inside, etc.).

I replaced them this past weekend with new IPF housings. During the process I noticed that one of the factory headlight plugs had seriously burned/melted in the past (see pic below) and the other had been replaced with a new pigtail crimped in.

http://www.flickr.com/photos/72188695@N05/7059042059/
Notes:
-when I bought the vehicle, it did not have a chassis ground & I didn't know it for a few weeks).
-upon removing the headlight, it did not appear that the plug was melted to the bulb socket, leading me to believe that the current headlight install may have been after the fact
-I've replaced both headlight pigtails

Now with the new headlights installed, the low beams work great. However, when I switch on the high beams, half the time the go completely dark. The other half of the time they go dark for about 5 seconds before coming on....

So my question is, can the factory wiring/relay handle the H4 bulbs? Am I at risk of burning up my headlight switch?

I've ordered this kit already hoping it will fix this. However, it will likely be a week or two before I can install it. I'm concerned about what damage I may be doing in the meantime.
http://www.wildhorses4x4.com/product...ormance_Lights

 

Yes, no problem with most H4 bulbs, of course depending on the wattage, same pinout. Likely you are seeing dirty contacts on the headlight/combo switch:
- http://www.4crawler.com/4x4/CheapTri...eadlight_Combo

 

^^ I used 4crawler's diagram to build my own upgrade harness and it works flawlessly including the hi-beam indicator still coming on.

It was a fun project and the light output difference was amazing to say the least.

I'm sure the factory wiring will handle whatever you have in there but an add on harness will really make a huge difference.

 

The factory harness, relay, etc will handle a 55 / 60 Watt H4 bulb with no problems but if you are looking at 90-100 Watt high beam bulbs you better beef things up like aa1911 suggests.