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914World.com _ 914World Garage _ H4 headlight relay question

Posted by: SKL1 Jul 3 2014, 01:22 PM

Putting in new H4 headlights with the 100W high beam and utilizing the "relay" to protect the OEM wiring.
Using the relay and new lights from Pelican and have checked and rechecked my wiring several times. Fused power from battery to #30. #85 to ground. #87 to high beam terminal of each light, #86 to old headlight wiring on one side, and taped off the other as recommended.

I have 12V into relay when high beams are on, and good 12V from battery, but neither high beam works thru the system, though low beams work. Fuses all good- new JWest fuse panel. Bulbs new and work fine when bench tested.

Any ideas???? Have 2 new relays from Pelican and have tried both...

('73 2.0)

Posted by: Cap'n Krusty Jul 3 2014, 01:32 PM

You need one relay for the low beam, one for the high beam. If you've separated left and right, then you need 4 relays.

The Cap'n

Posted by: ClayPerrine Jul 3 2014, 01:47 PM

For one side you will need two relays, one for low beam and one for high beam.

Low beam relay:

Pin #30. Power for lights.
Pin #87 Output to Low beam Filament in bulb.
Pin #85 Low beam wire from factory harness.
Pin #86 Ground.

High beam relay:

Pin #30. Power for lights.
Pin #87 Output to High beam Filament in bulb.
Pin #85 High beam wire from factory harness.
Pin #86 Ground.

You still need the ground wire on the back of the bulb to ground it. Run it and the relay grounds to the ground point for the headlight motor.

I mounted mine under the headlight bucket. I used the JWest 911 headlight harness kit, and added an inline 30A fuse and longer, heavier wires all the way back to the battery to prevent voltage drop. I used the same gauge wires as the main electrical feed wires in the chassis harness.

It makes a real difference in light output having the brighter bulbs. Plus, I have an early 911 headlight switch, which is very expensive these days. Taking the load of the headlights off the switch will make it last much longer.

Posted by: Luke M Jul 3 2014, 02:31 PM

I found this drawing awhile back.
Hope it helps.

Attached image(s)

Posted by: ClayPerrine Jul 3 2014, 02:47 PM

That is a good diagram, with one flaw.

The original ground wires for the headlights are of a too small gauge to prevent voltage drop with the bright bulbs. Use a new ground of a larger gauge from the bulbs to the ground points next to the headlight motors.

Posted by: SKL1 Jul 3 2014, 02:56 PM

great suggestions guys!!

another project for the 4th!!

Posted by: Dave_Darling Jul 3 2014, 02:57 PM

You don't have to have relays for the low beam if you keep to the stock wattage of low beam. It's not a bad idea to have one, mind you, but it's not necessary per se.

If you have a relay that is able to handle the current for both lights, you can use only one relay for the high beam of both. You'll want to have a wire from the #87 terminal of the relay to the power connection on each light. (And another relay for the low beam of both if you go that way.)

The four-relay setup above is the best setup (offloads almost all the headlight current from the ignition switch and the headlight switch) but is the most complex.

Clay's point about the grounds for each light is a good one. The ground wires should be at least as thick as the power wires, and they should connect snugly to a solid part of the chassis!

Troubleshooting your current setup:
- Do you definitely have ground at pin #86 on the relay?
- When you trigger the high beams, do you actually have +12V (hopefully more like 14V!) at pin #85 of the relay?
- Do you have power at #30 of the relay?
- Do you see +12V at pin #87 when the high beams should be on?
- Can you jumper straight from #30 to #87 (use a nice thick wire!!) to get the high beams on?

--DD

Posted by: Drums66 Jul 4 2014, 01:24 PM

.....Low watt H-4's,,,,no relay's(I have no issues)

Posted by: SKL1 Jul 4 2014, 02:40 PM

This car will spend its life in AZ- it is VERY dark there at night as they don't believe in street lights etc. I need the 100W high beams!!

I see JWest has a early 911 relay kit- gonna see if that may work too...