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Old 09-30-2007, 07:27 AM
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h4 upgrade

I just bought a set of h4 lights to replace the stock lights in my 85 chev pickup. I put the low beams in first and then tried them, they work great, then I installed the high beams, but when I tried the lights, the low beams dimmed down. Can I fix this by installing a upgraded wiring harness with relays or could this be a deeper problem. Thanks in advance.
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Old 09-30-2007, 08:09 AM
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You may need to go with a heavier wire for the headlights, this is usually suggested when upgrading headlights to higher lumen output
Shane
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Old 09-30-2007, 09:38 AM
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would the upgrade kit with the relays that draw directly from the battery help?
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Old 09-30-2007, 06:51 PM
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You do not need an upgrade wiring harness, all you need is a couple of relays and some #10awg wire. The lo beam wire from your headlamp switch goes to the relay coil of one relay. The hi beam wire from your headlamp switch goes to the coil of the other relay. Both of the other sides of the coils go to a ground. Each relay has a normally open and a normally closed contact. You will provided a fused 12 volts to one side of each normally open relay contact. The other side of the normally open contact will go to your lo beam headlamps. The other side of the normally open contact will go to your hi beam lamps. You should use two 30 amp fuses.

Here is a schematic showing relays, compliments of Doc.

The attached pdf file is a bit simpler and easier to understand.
Vince
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File Type: pdf headlamps.pdf (12.0 KB, 102 views)

Last edited by 302 Z28; 10-01-2007 at 09:30 AM.
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Old 09-30-2007, 09:13 PM
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The headlight relay upgrade that is sold by LMC truck (and others) should solve your problem. You could buy most of the parts together to make the relay set yourself , but its only about $30 for the complete kit. The kit includes new plugs for the back of the headlights so that you don't have to cut the existing wiring to splice in the relay wiring. The kit price is very reasonable, considering the parts cost and time savings.

Bruce
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Old 10-01-2007, 05:37 AM
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Quote:
Originally Posted by 75gmck25
The headlight relay upgrade that is sold by LMC truck (and others) should solve your problem. You could buy most of the parts together to make the relay set yourself , but its only about $30 for the complete kit. The kit includes new plugs for the back of the headlights so that you don't have to cut the existing wiring to splice in the relay wiring. The kit price is very reasonable, considering the parts cost and time savings.
Bruce
Just make sure the wire size is sufficient. I have seen some kits that have #14 or #12 gage wire. #10 should be considered optimal.

Vince
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