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Old 05-25-2005, 07:34 PM
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Is F-150 headlight relay in switch

I'm attempting to adapt the 1981 F-150 wiring to the rat project and I don't see a headlight relay with the wiring I stripped off the F-150 or in the wiring diagram I have. It appears, based on the size of the wiring, that the relay might be inside the switch itself. Anybody know if this is the case?

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Old 05-25-2005, 08:33 PM
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As far as I remember the 81 F150 has no headlamp relay, either external or internal to the switch. The switch carries the entire load.....I think.

Vince
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Old 05-25-2005, 09:49 PM
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Thanks Vince,

Here is a pic of the switch if you can tell anything from that. The large black/orange wire on the left comes directly off the alternator regulator (no relay) and appears to be the large capacity wire to feed the headlights.

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Old 05-26-2005, 04:42 AM
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Yep, that is the bugger. I also think the switch has a built in circuit breaker.

Vince
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Old 05-26-2005, 06:47 AM
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Quote:
Originally Posted by 302/Z28
I also think the switch has a built in circuit breaker.
Hope so because I can't find a fusible link anywhere in that heavy wire coming in from the regulator (according to my manual, Ford used in-line links and not the plug in modular fuses for the F-150). Also the wiring diagram does not show a fusible link in any portion of the headlight system. Guess I'll just wire it up and keep the extinguisher handy.
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Old 05-26-2005, 07:45 AM
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There was no relay in that circuit. The switch carried full amperage. FORD had trouble with the trucks that had marker lamps on the cab as the required amperage through the switch would actually melt it. The only circuit breaker is for the tail/brake lamps.

You really need to put the headlamps on a separate circuit via a relay.
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Old 05-26-2005, 08:08 AM
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Quote:
Originally Posted by KULTULZ
You really need to put the headlamps on a separate circuit via a relay.
I strongly agree.

Vince
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Old 05-26-2005, 10:32 AM
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-TECH ARTICLE-
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Old 05-26-2005, 11:47 AM
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Great "how to" Kultulz. Thanks for the following up.
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Old 05-26-2005, 01:12 PM
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I found two new relays in my electrical drawer but I don't recall now what amp rating they were when I got them. I don't see any markings on the outside that sound like a rating number. They are marked with the normal 30-85-86-87 and 87a for the tabs but the only other numbers on the case are 49400 on the top of each of them and then one is stamped with a 030 on the back and the other is stamped 103 on the back. Are relays typically 20amp or might these be lower.
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Old 05-26-2005, 04:47 PM
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Quote:
Originally Posted by cboy
I found two new relays in my electrical drawer but I don't recall now what amp rating they were when I got them. I don't see any markings on the outside that sound like a rating number. They are marked with the normal 30-85-86-87 and 87a for the tabs but the only other numbers on the case are 49400 on the top of each of them and then one is stamped with a 030 on the back and the other is stamped 103 on the back. Are relays typically 20amp or might these be lower.
Those relays typically are either 10 or 20 amp. You can get 30 amp relays in th same format.

Vince
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Old 05-26-2005, 05:47 PM
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Any way I can test or tell for sure what these are?
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Old 05-26-2005, 07:18 PM
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Quote:
Originally Posted by cboy
Any way I can test or tell for sure what these are?
They will probably handle the load you require, but these things are cheap. Trash them and buy some that you know the amperage of and play it safe.

Vince
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Old 05-26-2005, 07:35 PM
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The headlight switch has a thermal circuit breaker in it. It will cause the headlights to blink when it gets too hot. This will most likely happen when the lights are on bright for a extened period of time. The relays are not a bad idea to keep the load off the switch.
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