308 QV US Electrical Anomaly of this season

I'd be interested in knowing about the power situation for the headlight motor. Sounds as if it's demanding more current than it should.

 

Motor could be going bad, it has too much resistance that will cause the fuse to get hot and blow.

 

By "headlamp motor relay" do you mean the "relay for headlamps lifting motor" as it's called in the '84-'85 US 308QV OM?

If so, does the "relay for external lights" (that's the oddball ...006 relay) also buzz when the "relay for headlamps lifting motor" buzzes?

If you remove the "relay for external lights" when the "relay for headlamps lifting motor" is buzzing, is there any change?

 

Your thread title doesn't go far enough -- it should be "the Electrical Gremlin of the Century"!

Please also confirm that the fuse in question is the seventh from the left of the LH fuseblock. What's weird is that this fuse has nothing to do operation of the relay for headlamps lifting motor (this fuse supplies +12V power to the RH headlight motor relay and LH headlight motor relay). Wouldn't hurt to also remove the RH headlight motor relay and LH headlight motor relay and see if that changes things with regard to the buzzing and the fuse blowing -- also will give you a chance to give them a light shake and see if anything is broken inside and rattling around (also wouldn't hurt to check for any loose bits inside the relay for external lights and the relay for headlamps lifting motor).

Will await your report.

 

Yes, for diagnostic purposes, it's unfortunate to have only one of the ...006 relays; however, for a test, you can replace the ...006 relay with a ...113 relay (like the horn relay), reinstall the ...101 LH & RH headlamp motor relays, and see if the headlights then work OK or if you have the same trouble.

(I think the only downside of using the ...113 relay in the ...006 relay position might be something like the exterior running lights also flashing when using the stalk to flash the headlights, but, for just the normal headlight operation either should work the same.)

Also, did you ever just try using a different ...101 relay for the "relay for headlamps lifting motor"?

 

Didn't I mention that Step 0 in chasing electrical gremlins is: "check for dodgy modifications"?

It's not uncommon for the gauge needles to move maybe 1/2~1 needle width when the dash lights are turned "on" and the dimmer is set to maximum brightness, but your "20%" sounds a lot more than that -- is it? If so, it indicates that the ground connection for the gauges and dash lights (which is shared) is not so good. On your rear defroster warning light, there are two terminals: one has a single L (blue) wire and the other has two N (black) wires (swagged into a single female terminal). One of those black wires is the ground, and runs to a common grounding point with many connections. As a test, if you add a jumper connecting those two black wires to a known good ground and the gauge needle movement is greatly reduced = a strong sign that the connection at the common grounding point is not good. Alternatively, you could permanently install that jumper in the central tunnel if it helps things, and I wouldn't call that 'dodgy"

 

I don't know. On the OM schematic, it's shown as a single point where about 8 different wires are connected. My guess would be that it would either be sort of behind the relay panel or maybe in the passenger footwell area, but could be anywhere on the front firewall or even maybe in the forward part of the central tunnel. Hopefully, another '84-'85 US 308QV Owner can chime in on its location.

However, this ground network for the gauges is a "daisy chain" affair so if you've got some gauges that have the problem and some that don't = that would more signify the trouble is in one of the swages of the daisy chain. If all the gauges show the same problem = more likely it's at the common ground point connection. But adding that jumper should improve things for the gauges (i.e., reduce the needle movement with the dash lights "on") even if all is OK as stock.