Wiring Issues

[AzNomad]

I'm completely rewiring my 79 J10 and I've got a few questions I'm hoping some of you guys might have the answers to.

The previous owner left a 21 circuit painless wiring harness in the truck, it was factory fresh so I decided to use it. However, there are two issues I have with it. First off, the headlights I have are Halogen, and according to painless I'll either need a relay, or to get new LED lights. But to be honest I cant quite understand why I need the relay, I know the halogens draw more power, but it seems that the previous wiring did not use a relay and I know they worked well. So do I really need the relay?

Secondly, the painless kit also does not include any mention of the ignition module on my truck. I assume this is because its a universal kit but I'm not certain. If you have any experience routing a painless kit to an ignition box I would greatly appreciate any advice.

If anyone has any knowledge of these issues I am all ears.

[dodgerammit]

The halogens didn't work as good as you believe. Trust me. Factory wiring on older vehicles route the current through the headlight switch. Installing relays separate the current path and switch.

That said, since installing the Retrobright LEDs in my Wag, I'll never buy another sealed beam. Even with Relays, the halogens.... well, suck. Just replaced the ones in my YJ with another set of Retrobrights. The Eagle is next on the list. Pricey? Yeah, but Amazon LEDs are junk. You get what you pay for with these. They're Morimoto units made for Holley to target the classic vehicle market.

You can chose your color temp. They offer OEM style classic white and current style modern white.







As far as the ignition module, I'd check oljeep for the wiring diagrams. Or, if you want to upgrade, ditch the duraspark module before it leaves you stranded and put something like a basic MSD box in its place.

[tgreese]

Painless should have given you a wiring diagram with the harness. A '79 Jeep has a Ford/Motorcraft Duraspark ignition system with a distributor made for the AMC engines. If the harness was not explicitly meant to work with the Duraspark system (not Duraspark II) you will need to figure out how to merge the harness with your ignition.

There are many diagrams of the Duraspark ignition online, like this one.

durasparkdiagram (608 x 363).jpg

Search for "Duraspark ignition diagram." (Note there are lots of pages out there with stuff about Duraspark that is just random web scrapings and meant as clickbait. Be careful what you click on.)

You will need to reconcile your harness with the way the Duraspark is connected, unless the harness was specifically designed for the Duraspark. As mentioned above, you can look at the factory wiring diagram for another example of how the Durspark stuff is connected.

Regarding the relay, I'd just go ahead and install it. Your switches - both the dash switch and the dimmer switch - will last much longer with the relay in there. And your lights will be brighter if you use a short heavy wire to supply power for the lights. Cheap and easy upgrade.

[SJTD]

I agree. You may not need them but you're better off with them.

[tgreese]

I wrote an article about headlight relays several years ago. It may be a lot of text to plow through for some.

https://www.martinos.org/~reese/RelaysArticle.pdf

Please ignore the part about fusible links. Suggest you use a circuit breaker like I did, or a fuse if you must.

[Yeller]

Yes you need a relay… the headlight switch and high beam switch will be unhappy with the current draw unless you use old sealed beam or LED headlights. The switches were only marginal even with old school sealed beams.

[will e]

Welcome to the board! Where is AZ are you located?

[AzNomad]

Thank you guys for the responses, I'll put the LED's on the wish list for now and install the relays for now. As for the ignition module, I'll have to look into the MSD for the future as their a bit pricey, but I suspect I can manage the Duraspark with the painless module for a bit.

[dodgerammit]

Thank you guys for the responses, I'll put the LED's on the wish list for now and install the relays for now. As for the ignition module, I'll have to look into the MSD for the future as their a bit pricey, but I suspect I can manage the Duraspark with the painless module for a bit.

I did the economy version of the MSD. The MSD Streetfire ignition unit worked great for my purpose for several years til I did the engine swap.
They run about 30% less than the more common 6AL.

[candymancan]

Not sure about (heavy wire) needed for headlights. 6 feet of 16ga wire can handle 10 amps without any noticable power loss. 65wx2 is 130w divided by 13.5v is 9-10 amps. The switchs gets power from the fuse panel.. thats a short run.. and the switch to headlights isnt very long of a run either. 14ga wire would the max size you need.. 16ga will be fine too except maybe the passenger light which would see the longest run of wire.

If you installed a relay in the engine compartment and the headlights got power directly from the battery and your relay had a simple 18ga trigger wire in the dash. You could easily get away with 16ga wire then for sure

Check the voltage supplied at the headlight wire itself and check the voltage at the switch. Then the battery and see what your power loss is

[tgreese]

The wire size issue is more about the resistance of the wire, the length of the wire, and the contact resistance of the many additional switches and connectors. 16 ga wire has more than four times the resistance per unit length as 10 ga wire. The circuit will work fine with the smaller wire, but larger wire and fewer connections will make an clear improvement in brightness. Lots of detail about this in the PDF I attached.