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Old 07-12-2019, 10:06 AM   #1
Bricktothefuture
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Default '89 headlight harness in '79

One last thing to pass NH inspection.

I got tired of exploding and overheating light switches in my '79. Pulled an entire headlight harness from a known good '89. I can't find the correct wiring diagram - closest thing is an '87 on the wayback machine, but it looks like the colors have changed a bit. I have the following wires I need to connect.

Yellow wire coming right off of the switch
Blue/White wire coming off of pole 87 on the relay
Green/Red coming off of pole 30 on the relay
White wire coming off of pole 87b on the relay
I connected the heavy yellow wire coming from pole 87 to the yellow wire going back to the headlight relay.

I've tried various ways of hooking these up and I can't get it right. Lights are either always on or don't work at all.

If I go by the '87 diagram, the white wire goes to the bottom two fuses with the parking lamps/side indicators. Red/green to constant power., and blue/white to switched power. I can't figure out the yellow one - on the '87 diagram it looks like it goes to fuse 1, but that would run power right to the switch, which is what I'm trying to avoid by using this setup.

Help!
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Old 07-12-2019, 11:41 AM   #2
Bricktothefuture
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update - everything works with the blue/white wire from the relay disconnected. Not sure if this serves an extra purpose on the 89?
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Old 07-12-2019, 02:36 PM   #3
cleanflametrap
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The switch in the 89 is a low current switch compared with the one from your 79, despite the fact the 79's switch exploded. The 89 used an external relay, called the "headlight relay" to handle the current instead, keeping the current through the switch just what the relay's coil needs.

You didn't add the headlight relay, right?

I have a couple 89's and a '79, and the docs, so I can help you do this.

Edit: I can see by your terminal number you did add the headlight relay. The one under the hood usually called hi-lo or step relay to select high beam. Let me get the books out and match up the colors...

Edit: Compared 87 to 89 wiring diagrams for the relevant connections -- they're the same. That you have lights without the blue/white wire from the headlight relay connected to anything makes me think you have the wrong relay installed in the socket. The headlight relay is not just a common cube relay, it is dual pole single throw (two form a contacts) and not single pole dual throw (one form c contact) like most common cubes.
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Old 07-12-2019, 06:14 PM   #4
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Yep, I brought over the whole relay. Removed the direct wire from the junction to the headlight switch and went completely with the new harness, relay, and switch. Relay is Bosch 0332015006, correct for this application...
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Old 07-12-2019, 07:44 PM   #5
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I couldn't find a good wiring diagram either, so be careful if try this:

Pin 85 and 86 are the relay coil. One (85) should be a black wire to ground, the other (86) should be a yellow (?) wire to the light switch. This turns on the relay when switch is on.

Pin 30 is the main power to relay contacts - Green/Red, to battery.

Pins 87 and 87a both close to pin 30 in the relay when the coil is energized (assuming it's the correct DPST relay). You want 87 to go to the step relay pin 56. Sounds like this is your blue/white wire (but shown in other year's wiring diagrams as yellow too).

I'm guessing a bit here, but 87a probably provides power to the parking lights via fuses (white).
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Old 07-12-2019, 09:40 PM   #6
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Quote:
Originally Posted by Bricktothefuture View Post
...
Yellow wire coming right off of the switch
Blue/White wire coming off of pole 87 on the relay
Green/Red coming off of pole 30 on the relay
White wire coming off of pole 87b on the relay
I connected the heavy yellow wire coming from pole 87 to the yellow wire going back to the headlight relay.
...
Help!
The blue/white wire should not be on 87, it should be on 86. If 85 (black) is grounded like it is supposed to be, power switched through the headlamp switch in full on position energizes the relay's coil from 86 (blue/white).

Quote:
Originally Posted by bobxyz View Post
...
Pin 85 and 86 are the relay coil. One (85) should be a black wire to ground, the other (86) should be a yellow (?) wire to the light switch. This turns on the relay when switch is on.
Not yellow. Blue/white.

Quote:
Originally Posted by bobxyz View Post
Pin 30 is the main power to relay contacts - Green/Red, to battery.
Yes.

Quote:
Originally Posted by bobxyz View Post
Pins 87 and 87a both close to pin 30 in the relay when the coil is energized (assuming it's the correct DPST relay). You want 87 to go to the step relay pin 56. Sounds like this is your blue/white wire (but shown in other year's wiring diagrams as yellow too).
Not blue/white. Yellow.

Quote:
Originally Posted by bobxyz View Post
I'm guessing a bit here, but 87a probably provides power to the parking lights via fuses (white).
Exactly. Also, if the blue/white is doubled in socket 86, the second blue/white wire went to fuse 14 for rear fog lamp, so in that case there is more than just a relay coil load for the headlight switch contacts; there is also the single rear 21W fog.







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Old 07-12-2019, 10:51 PM   #7
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I re-read the original post and realized there must be a typo or confusion between yellow and blue/white wires:

Quote:
Originally Posted by Bricktothefuture View Post
Yellow wire coming right off of the switch
I connected the heavy yellow wire coming from pole 87 to the yellow wire going back to the headlight relay.
Blue/White wire coming off of pole 87 on the relay
Regardless of the wire colors,
- the headlight switch should connect to 86, and
- the step relay (56) should connect to 87
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Old 07-12-2019, 11:53 PM   #8
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Quote:
Originally Posted by bobxyz View Post
I re-read the original post and realized there must be a typo or confusion between yellow and blue/white wires:



Regardless of the wire colors,
- the headlight switch should connect to 86, and
- the step relay (56) should connect to 87
Yes, that's my guess as well. It is easy to look at the bottom of that relay and confuse the terminal numbering.
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Old 07-13-2019, 02:35 AM   #9
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Quote:
Originally Posted by cleanflametrap View Post
Yes, that's my guess as well. It is easy to look at the bottom of that relay and confuse the terminal numbering.
I’ll double check... odd.
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Old 07-13-2019, 04:22 PM   #10
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You can also just leave it with the stock wiring and install an extra wiring harness for the headlights. It gets triggered by one of the old headlight sockets. You can then run higher power bulbs. Typically you gain at least a volt or more increase at the headlight. I've been using this one for a few years now.
https://www.summitracing.com/parts/upd-34263
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Old 07-15-2019, 09:59 AM   #11
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Apologies for not having a chance to dig in to this yet. I think Art nailed it though - the extra blue white would normally power a fog light, which I don't have.
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