Now that its cold here in NY its about time I get the blower motor working in my truck. It needed a new pigtail on the blower motor resistor so I installed that but the blower motor still was not turning on. I checked the fuse and that is intact and fine. I checked the power at the fuse panel where the glass fuse clips into and there is no power there. I cant find any good wiring diagrams online and im trying to figure out how I can check the wires that send power into the fuse block?
Help with 1978 chevy truck fuse block power feed
- Thread starter joegreen
- Start date
Usually the fuse block is fed off fusible link(s) that tie in from the positive battery cable, AFAIK from the starter solenoid, that go to the main harness block at the firewall, maybe one of those has opened up? (I’m going off long ago memory here). These guys have some things that might be helpful- http://forum.73-87chevytrucks.com/smforum/index.php?topic=11768.0
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Thanks. Ill see what I can see in the light. Everything else seems to work.
The blower motor circuit would come through the ignition switch. This is a different circuit from the ignition-- it turns off with the key in the "start" position to send more battery power to the starter and ignition.
Also it was really common on 1970s cars for the fan switch to burn up.
Also it was really common on 1970s cars for the fan switch to burn up.
Yes i used a digital dvom to test for 12v at the fuse block pins for the heater fuse and there is no power. Other fuses on the block are receiving 12v so i know the ground was good on the meter
I will investigate the switch but for now power is not even going to the switch.
There will be a Brown Wire coming out of the Ignition Switch, This is the Accessory Power Feed Circuit. On some models there will be a Brown wire & a Brown wire with a White Tracer crimped together in the same terminal.
With the key in the Run Position....This circuit should have power, If not.....Separate the Ignition Switch Connectors from the switch & check for a melted Connector.
If the Connector looks good & all the Red Wires have power.....Time for a new Ignition Switch.
With the key in the Run Position....This circuit should have power, If not.....Separate the Ignition Switch Connectors from the switch & check for a melted Connector.
If the Connector looks good & all the Red Wires have power.....Time for a new Ignition Switch.
Roger that. Today I was removing the big red power wire from the junction block on the firewall to clean them up. Of course the studs on the junction block are molded into the plastic and the 43 year old plastic holding the studs cracked so now the studs just spin in the plastic. i will get that replaced.
That's the battery power feed for the High Blower Relay. Amperage is only drawn on that circuit when the Blower Motor in on High, Otherwise the Blower is powered through the Resistor Pack via the Blower Switch.
My truck does not have a/c so it just has the basic 2 resistor with low/med/high switch and one wire to the blower motor. This setup does not have the blower relay. I believe only the a/c models had the relay. This is a base model custom deluxe
I was going to remake a junction block in solid works and then 3d print the part and add my own studs back in. Anyway i needed to remove the old junction block so i could have it next to the computer while designing the new part. When I went to remove the junction block i flexed it and the two studs just fell out. This ended up being great because i decided just to add new studs to the old block instead of making the part from scratch. I bought some stainless bolts and nuts, drilled two holes in the junction block, put the bolts in and jb welded them in place. Yes the junction block is still cracked but the jb weld should more than enough to make the part rigid again
I think i have narrowed down the issue. When i check voltage at the heater fuse with the ignition in the acc/run position it reads 0v. But if i turn the ignition 1/8 of a turn more like i am about to engage the starter the heater circuit now reads 12v. I believe this means the ignition switch down on the steering column is bad.
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