OP
If you got the right Grant hub kit, it comes with the spring/plastic barrel/wire (with spring inside the white barrel). Depending on what "style" (read Signature Series Grant wheels use a different install method with instructions on the BACK of the included Grant install instructions included with hub. In that case you take apart the white plastic tube (shown in post # 7) and discard the white plastic tube and round end brass part and just use the white plastic cap/wire and the spring. That goes inside the tube hole on the hub. Use some tape to hold that white cap/wire/spring inside the hub while you then put the wheel on.
BTW if you ever lose or FU that spring, a ball point pen spring works perfectly
You will have to make a short jumper wire using a ring and spade terminal to connect to one of the male spade nipples on the horn button. Either one will work but I plug in the short, included wire to center of cap and the short jumper wire to the outer one. The short jumper you make is connected to one of the 3 steering wheel to hub bolts. IMHO the kind of horn button you have is WAY better than the spring under the horn button type on cheaper models.
I have Grant wheels with that kind of button on my 67 and 72 C10. Works great
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