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87 911 Carrera 3.2 headlamp circuit (100w bulbs)


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I have your fuse panel ver 1.3 installed up front on my 87 911. The previous owner may have upgraded the headlamp bulbs. The low beam (dipped) circuit (position 1 & 2 to the left of the H and headlamp relays) keep blowing their 7.5 amp fuses. My Porsche mechanic insists on replacing the 7.5 fuses with 15 amp fuses for those two positions. Is the purpose of the "H" lead to correct this situation? If I run a lead from the battery to the H position, will I be able to drop back down the the proper "8amp Max" fuses at position 1 & 2? I've read your documentation on the H position but it doesn't explain if this is a way to mitigate blown fuses on the low beam circuit. Final question...what ga wire should be used from the battery to the H lead? Thank you. 

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Check the bulb wattage rating.  If you are blowing a 7.5A fuse then either each of your bulbs is greater than 100W (7.5A x 13V = 97.5 Watts) or there is another issue ( like bad contacts/wiring in the bulb connector).  
 

If they are 100W bulbs then you might need to go to 15A fuses since the 7.5 would be marginal as calculated above.  15A should be ok since the standard Porsche headlamp wiring is 1.5mm2 wire which is good for 20A so the fuse will blow before the wire melts!
 

The H terminal can be used to provide another ‘way in’ to the fuse panel from the battery so the current is not all carried down the single factory thick red wire (which is good for about 40A).   Fit a 2.0mm2 or similar red wire between H and the battery + if you really do run 100W bulbs to spread the load. 

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  • classicretrofit changed the title to 87 911 Carrera 3.2 headlamp circuit (100w bulbs)

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