How much amperage do you think GMC headlights pull?
 

I guess there's a "headlight relay" mod that's all the rage with the kids nowadays and I'm gonna try and look cool by doing it myself.

Now the question is what size fuse/circuit breaker should I use between the new hot wires and the relays?

Thank you everyone.

Re: How much amperage do you think GMC headlights pull?
 

Need to know the amps or watts of headlights you are using to answer that question. The relay "mod" simply allows power to go directly to headlights instead of being channeled through more wire and a usually old switch with not so good contacts resulting in brighter headlights. Even with a new switch the results are positive with a more direct path for the power.

Re: How much amperage do you think GMC headlights pull?
 

I would say 10 amp for low and 10 amp for high. It really comes down to using a fuse that is a little less than the amperage than what the wire you use can handle.

Re: How much amperage do you think GMC headlights pull?
 

Here is a good thread I remer on the headlight relays.

Link;https://67-72chevytrucks.com/vboard/...eadlight+relay

Hope this helps.

Re: How much amperage do you think GMC headlights pull?
 

The old style round headlights were typically 55/65 watts.
The low beams pulled 55 watts. The high beams pulled 65.
With the two low beams on the car pulls 110 watts combined.
(110 watts divided by 12 volts gives you 9 amps).
Add in the high beam at 130 watts combined and you're sucking down about 11 amps.
All four headlights on will draw 20 amps.

Re: How much amperage do you think GMC headlights pull?
 

Thank you very much everyone, that answers my question.

Re: How much amperage do you think GMC headlights pull?
 

This thread indicates the headlight is 'fused' at 30 even though it's a thermal circuit breaker.

Re: How much amperage do you think GMC headlights pull?
 

Accelo is spot on with this information. You need two relays to operate low & high beams. If you use a single fuse for both relays 25A or 30A would be sufficient since your load should not exceed 80% of the fuse rating.

Re: How much amperage do you think GMC headlights pull?
 

Would it make sense to actually run a fuse for each relay so if the fuse blows I'd still have low or high beams left?

Body bolt, that is rather interesting, and rather conservative coonsidering they may use approximately 10 amps less than "30"(which is subjective).



Hey can anyone verify if the GMC trucks headlight harness actually has two Light Green wires coming from out of the firewall for the hi beams instead of one for Chevy harnesses?
I'm assuming this is for the extra bulbs and amperage draw?

[QUOTE=jumpsoffrock;8976161]Would it make sense to actually run a fuse for each relay so if the fuse blows I'd still have low or high beams left?
/QUOTE]

Yes, Running separate fuses for each relay is the smart thing to do for the reason stated. Two 15A or 20A fuses will work.
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Re: How much amperage do you think GMC headlights pull?
 

I thought about two fuses, but using this junction block, I can disconnect either or both relays.
The factory harness runs left to right in the photo, behind the relays under the fender lip.

I cut the green wire and crimped insulated single spade connectors to both cut ends. A short pigtail with spade connector connects the one green wire to the relay connector. Another pigtail with spade connector from the relay output, connects to the other end of the cut green wire.

If the relay should fail. I can disconnect all the spade connectors and plug the two green wire ends back together. Power for the headlights now comes directly from the dimmer switch to feed the lights as it did originally. If you should try this, you have to observe which male/female connecters are used and where.

I did the same with the tan wire and that relay. I did this some time ago and do recall that one of the Hi/Low wire(s) was doubled coming out of the bulkhead connector. Can't recall which, but if you say green, it probably is. I just stripped both wire pairs and crimped them into the same spade connector(s).

Sorry, I'm too lazy to go out and move the truck back and look under the hood.