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I have an ‘81 with the headlight relay setup. The lights have been working well for years. All of a sudden they go out when I hit a bump in the road. Then come back on. The car does it on low and high beams. Sounds exactly like a loose ground right? I have checked every ground for the headlight system. All are tight. What’s my next item to check?
I may be mistaken, but didn’t you install the relay mod to your factory wiring? If that is the case, can you gently tap on the relay? It could be the relay is failing, does one relay operate hi and low beams. Relays go bad, on my Craftsman Garage door opener there is a motion sensor that turns on two light bulbs. Of course the tiny relay went bad and I was forced to purchased a new PC board for $ 75. Then I got smart, and bought the exact relay from our friends in China. I replaced the relay on the PC board and when the second pc board failed, I was ready with a replacement.
Yes I have the relay mod. Low and high beam lights each have a separate relay. That leads me to believe that the problem may be upstream of the relays. Headlight switch or dimmer switch possibly.
I remember being on the side of the NY thruway, in the rain, trying to open the hood (the cable chose that moment to break) so I could whack the damn stuck relay.
Your car has the dimmer switch on the column, I am guessing? If so, you could by temporarily bypass the switch (maybe at the bottom of the column), easier than replacing the switch. Good Hunting
I don't have a 81 drawing but I do have a 80 and the feed from headlight switch to dimmer is a 2.0mm Yellow wire.
Output from dimmer switch:
Low, wire color Tan
High, wire color Lt.Green
Today's plan...
Jiggle the left headlight wires while the lights are on.
Test the outputs on the dimmer switch (If I can get to it).
Lastly test the wires at the light switch (fun to access).
You ALL have been very helpful so far.
Craig
I remember being on the side of the NY thruway, in the rain, trying to open the hood (the cable chose that moment to break) so I could whack the damn stuck relay.
i believe the headlights ground to the header bar that the headlight bodies mount to. that header bar is mounted to fiberglass inner fenders and fiberglass nose. it has to be grounded to the real frame or engine block.
Today's plan...
Jiggle the left headlight wires while the lights are on.
Test the outputs on the dimmer switch (If I can get to it).
Lastly test the wires at the light switch (fun to access).
You ALL have been very helpful so far.
Craig
With headlight switch pulled to HEAD you should have voltage at the dimmer switch Yellow wire, if not then test not fun light switch access...
i believe the headlights ground to the header bar that the headlight bodies mount to. that header bar is mounted to fiberglass inner fenders and fiberglass nose. it has to be grounded to the real frame or engine block.
That is the ONLY ground that I haven’t checked yet.
The ground(s) for the headlights originates at the alternator ground 5/16" bolt rear casing. From there it travels through the split conduit splices, lands at L&R headlights. The lower left, top center & lower right of core support are the ground eyelets anchoring points.
At least on my 77 and if the 80 drawing is accurate it is the same.
Last edited by bmotojoe; Sep 20, 2022 at 01:18 PM.
I remember being on the side of the NY thruway, in the rain, trying to open the hood (the cable chose that moment to break) so I could whack the damn stuck relay.
I was on the side of that same thruway when the fuel gauge on my old c4 got stuck and I ran out of fuel....$75 for 2 gallons of fuel btw from the authorized thruway service crew.
attach a wire to the headlight ground and run it to the engine, alternator bracket, whatever...
I finally got the opportunity to do it this morning.
I ran a 10 gauge wire from the horn and headlight ground to the ground on the alternator.
The alternator is grounded to the frame also.
I will test tonight on some real nice bumpy roads.
I can’t replicate the problem by shaking wire connections and such in the garage.
It seems that next step is to drop or pull the column to access the dimmer switch for testing.
Test drive later tonight.
Headlight issue.
