67 wiring harness question

[HIGHWAY BY THE SEA]

From what I understand the 67 wiring harnesses are different than the 68-72 ones. I have a 67 GMC 3500 that I removed the bad wiring harness from. The 67 Chevy C10 front clip that I bought (not picked up yet) has what is supposedly a good wiring harness in it. Can this 67 Chevy wiring harness be modified to work with my two extra headlights in the GMC? And other than headlights, should everything else work with it?

[chewychevy67]

The signal plug may be different because of the light location but unsure but It can be modified I'm sure. The under dash harness is the same for both as long as both were optioned the same. Good time to add a headlight relay kit.

[michael bustamante]

you can splice them in to work. im doing a GMC conversion now to my 67 c10. the park lights you have from the light socket to the rad support will fir in the 67 harness youre getting (1 year only on those plugs) they will not be a direct plug in for any other year. as for the hi beams, youll have to splice in you hi beam pigtails to the new harness. I do have a extra pair if you need them as well as 1 67 parklamp harness

[VetteVet]

Excellent advice given.

The tan and green wires from the dimmer switch control the high and low beams so it is relatively simple to wire the two extra lights into the high beam relay.

Here are two examples of the relay mod.

Single light two element bulbs AKA Chevy.






The four light GM relay mod.





It should be easy to see from the diagrams how the conversion is done.

['68OrangeSunshine]

Just a footnote on the Model Year 1967. In normal operation the Parking Lights go out when the Headlights go on.
The same fixtures became Running Lights in MY 1968 by federal mandate.
[I was confused by this when I bought '67 after having a '68 for 20 years.]

[HIGHWAY BY THE SEA]

Well, I just bought a 72 GMC headlight harness in a set of items from a parts seller. I wonder if this will work in my 67? Will I have to modify some wires due to the fact that the front marker lamps do not illuminate when the headlights are turned on? Or was this compensated for in the wiring after 67 so this will be plug and go?
If this harness works, I will use the side marker wires for any auxiliary lights I install later.
The only real differences I found in the two was that there was an extra light green wire, the purple wire that is on the 67 is brown on the 72, and there are two extra wires in the 72 bulkhead plug that are not in the 67 one.

[GMCPaul]

I'm currently out of town at my parents so I can't look at my GMC wiring diagrams to tell you all the differences but the 72 fuse block connection isn't the same as the earlier 67-68 fuse block so that portion of harness would be a issue.
Paul Sr @ GMCPauls

[HIGHWAY BY THE SEA]

Thanks for the reply Paul. If this 72 harness is not compatible with my 67, I will harvest the GMC headlight plugs from it and splice them into my 67 Chevrolet wiring harness.
Most of the wires match, but you are the real expert, so I await your final response!

['68OrangeSunshine]

I found the connectors for the '67 Parking Lights were slightly different from the MY '68 Running Light connectors. This is the connection that has a junction thru the radiator bulkhead. On the '67, the spade terminals inside the plug have one vertical and one diagonal [ -- /]. On the MY '68 it's one vertical and one horizontal [ -- l ].
When a deer took out the grille on my '67 K/10 Suburban, and I got a grille off a '68 Sub, I found this out. I swapped in the '67 Parking Light fixtures onto the '68 grille. The fixtures were identical otherwise.