Heater/A.C. and alternator wiring help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**68350** · 02-27-2018, 09:28 PM

Ok this is for a 68 c10 with factory air. I have power at the fuse box for the heater 25 amp fuse. However with the key on the brown wire going to the fan switch doesn't have power. Does this mean the brown wire has a break somewhere? My fan doesn't work at any speed. Also my alternator wiring has 4 wires, white-blue-red-black. My other 68 has the same wires with the black hooked up. My 72 has no black wire to alternator. On the 68 in question the black wire isn't hooked up to anything on the alternator. Do I need to hook it up or is it ok without?

**dmjlambert** · 02-27-2018, 11:58 PM

Trace the black wire to see where it comes from. I think you will find it is a ground wire. You may find everything is working without the wire connected to the ground on the alternator because the alternator is also grounded to the engine with the brackets. I recommend connecting it, because there is no such thing as too many grounds.

You may find the brown wire isn't getting power because the fuse is faulty or the fuse clip is rusty. Clean the fuse clip thoroughly and after putting it back in check for 12V at both sides of the fuse. If still no voltage on the brown wire, it is possible it is disconnected from the clip or broken.

**dmjlambert** · 02-28-2018, 12:07 AM

Wiring diagram
http://67-72chevytrucks.com/vboard/s...&postcount=302

Also check the connector at the fan switch, make sure your connector is in good shape, not melted like mine was. You didn't mention how you checked for voltage on the brown wire, or where along the wire you checked.

02-27-2018, 09:28 PM	#1
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Heater/A.C. and alternator wiring help Ok this is for a 68 c10 with factory air. I have power at the fuse box for the heater 25 amp fuse. However with the key on the brown wire going to the fan switch doesn't have power. Does this mean the brown wire has a break somewhere? My fan doesn't work at any speed. Also my alternator wiring has 4 wires, white-blue-red-black. My other 68 has the same wires with the black hooked up. My 72 has no black wire to alternator. On the 68 in question the black wire isn't hooked up to anything on the alternator. Do I need to hook it up or is it ok without? __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

02-27-2018, 11:58 PM	#2
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,626	Re: Heater/A.C. and alternator wiring help Trace the black wire to see where it comes from. I think you will find it is a ground wire. You may find everything is working without the wire connected to the ground on the alternator because the alternator is also grounded to the engine with the brackets. I recommend connecting it, because there is no such thing as too many grounds. You may find the brown wire isn't getting power because the fuse is faulty or the fuse clip is rusty. Clean the fuse clip thoroughly and after putting it back in check for 12V at both sides of the fuse. If still no voltage on the brown wire, it is possible it is disconnected from the clip or broken.

02-28-2018, 12:07 AM	#3
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,626	Re: Heater/A.C. and alternator wiring help Wiring diagram http://67-72chevytrucks.com/vboard/s...&postcount=302 Also check the connector at the fan switch, make sure your connector is in good shape, not melted like mine was. You didn't mention how you checked for voltage on the brown wire, or where along the wire you checked.



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