72 Pontiac Headlights

Terry Broussard

Terry Broussard

Cruising home from the local car show last night when I applied the hi-beams on the Pontiac. Lost all headlights, which made for an interesting last mile on the dark road. Parking and turn still work.

New headlight switch was installed some time ago.

Following the test procedure, I do not have any power on the red wire to the back of the headlight switch. Manual says fusible link.

I cannot find any visible direct red wire to the battery as indicated on the schematic, so I am thinking it must be on a wire wrap in the front engine harness?

Any thoughts as to where the fusible link is?

Thanks.
 
start at the dimmer switch always go to the last thing you changed if you have power there then go out from the with the test light. but my bets are on the replacement dimmer
 
John ED Renstrom said:
start at the dimmer switch always go to the last thing you changed if you have power there then go out from the with the test light. but my bets are on the replacement dimer
Click to expand...

Will do, but the switch had been working great for months. I did find the fusible links in the wiring harness, it was good.

I'll go back to the voltmeter....
 
Scott Crittenden said:
I had a 77 Caddy with a relay under the hood that went, same symptoms. Not sure when GM started using that set up.
Click to expand...

Scott the manual doesn't say anything about a relay, but I too had thought about that. Odd that I still have park lights, so there must be electricity to the switch.

I have ordered a new switch (both floor and headlight) since they are suspect as Ed recommended.

Thanks...
 
Terry Broussard said:
Scott the manual doesn't say anything about a relay, but I too had thought about that. Odd that I still have park lights, so there must be electricity to the switch.

I have ordered a new switch (both floor and headlight) since they are suspect as Ed recommended.

Thanks...
Click to expand...

Terry,
Good thread...I am also replacing my floor mount dimmer,since it causes the lights to go on/off(unintentionely).....I am just curious what part number you are using.....I have found a few differant ones for Cadillac,however I think its the same for Pontiac... being GM...the one I am replacing is not original to the car...so the numbers I have come up with are D804(Delco) 578005(GM) and DS72(aftermarket)...
Please let me know...thanks !!
 
So far everytime I have had this issue, the floor dimmer or the connector going to it has always been the problem. Not saying thats the issue but is the first thing I would check.
 
James Fischer said:
Terry,
Good thread...I am also replacing my floor mount dimmer,since it causes the lights to go on/off(unintentionely).....I am just curious what part number you are using.....I have found a few differant ones for Cadillac,however I think its the same for Pontiac... being GM...the one I am replacing is not original to the car...so the numbers I have come up with are D804(Delco) 578005(GM) and DS72(aftermarket)...
Please let me know...thanks !!
Click to expand...


I went to Autozone this time and picked up as Duralast UDS 419.

Still no luck in my case.
 
Here I go again,back in the day prior to strobes etc,we used the floor switch as kind of a flashing headlights limited only to how fast your foot would go.some that were mechanically inclined would as we say jimmy-jack flashing headlights to a hidden switch,not recommended,not factory.home made.:myopinion:
 
Terry Broussard said:
Installed a new floor dimmer switch and dash switch...no luck.

Back to the schematics.....
Click to expand...

Did you happen to pull back the carpet and check the wiring from the connector of the floor switch along the floor as far as you can? May be a bare wire rubbed into it form the years of feet running over the carpet. Worth a look. Thats the only idea I have since the floor switch was replaced.
 
Terry Broussard said:
I went to Autozone this time and picked up as Duralast UDS 419.

Still no luck in my case.
Click to expand...

Ok.....I will be dealing with mine tomorrow...I am using a DS-115(made by Eich).....according to Cadillac it should be a D-804(Delco) or 578005(GM) 0r numerous aftermarket including the DS-115......That is for 64-79 Cadillac Commercial Chassis..I would think Pontiac should/would be close..??
 
your think to much like your fixing a radio. toss the volt meter, use the prob test light. is there power to the dimer switch? there are only three wires to it. one power from the headlight switch one out to high beams one out to low. now if you have power to it from the switch, jump it with a test lead to either one of the other wires. if the lights come on it's the dimmer switch. if you don't have power its, the headlight switch. you have power to the headlight switch or you would not have parks. the headlight switch doesn't run threw the ignition. that was the reason for the separate fused on the power wire to it. it's a GM car you working on suspect that the power wire has pushed out of the plastic and is not making contact. feed back is so terrible in these circuits you get a false reading with the volt meter and the probe will let you check along the wire for the open. you get power to the dimer and jump the wire going out but still don't have lights it's the ground for the lights. the lights ground to the radiator support it grounds to the frame. it just came out of the shop. lots of banging, grinding, welding and all that. you may have just lost the ground from the radiator support to the frame. the lights pull a lot of current and need a good earth
 
The usual suspects

Terry- very often the culprit is with the ground wire(s), not the power. But maybe not here. Are you saying the headlights have a fusible link and NO FUSE on the fuse plate??? I'd look closely at the fuse plate with a flash light or use a tester (multimeter) to see if the fuse is blown. Also, my favorite tool is a light tester- clip the wire to ground and use the probe to touch the switch screws or clamps. It's a good way to at least see where the power is; then keep moving along the wire until the next place you can check to see if the power is still live. I'd also just to work backwards, do this first at the headlight sockets. Take the sockets off the bulbs and stick the tester probe in each opening. I'd bet you don't have power there based on your observations.
I find it takes a lot of little investigations and pondering on these electrical things. I wouldn't run a new wire unless you find the old one has not insulation on it.
Good luck
Kev
 
On a number of coaches I've owned....I've found fuse links above the transmission hump on the back of the firewall that were NOT listed in the diagrams. Might want to at least look there before doing any dreaded wire tracing or replacing components...Just my 2 cents worth of past experience.
 
So far today...

- no power at floor switch
- no power at red wire on main headlights switch
- POWER at brown striped on headlight switch
- POWER on both sides of fuse links on harness (two that i located on top of the valve covers)
- park lights still work
- all fuse panel fuses good

Leads me to think harness from fuse link to headlight switch?

Again, all four lights went out when I applied the high beams.

Moving on to the firewall search for hidden fuse links as suggested.
 
headlite switch

bet ya a cold adult beverage its the switch. the headlight switch . been there done it and tested everything and thought switch was good. wadn't good. no power and all and it was the switch. hey, i know but.......:my2cents::my2cents::my2cents:
 
Fixed...

Loose main front harness connector at the firewall. Probably as Ed suggested from jostling around for 7 months in a body shop or just loose from my install two years ago.

Now, on the fuel gauge.....
 
Darn GMs. I know there are a tone of wires going in and out of the switch but I never realize the tail and park were a separate power. so now the sending unit from my experience on the GM if it reads full it has a open. if it reads empty it has a short. seldom the gage most often the sending unit or the wiring in the rear going to it.

now if you can tell me why my 68 quits every now and then but restarts right up I'll have my gremlins captured. I'm up to the ignition switch on it now. they no longer make a factory replacement for it.
 
John ED Renstrom said:
Darn GMs. I know there are a tone of wires going in and out of the switch but I never realize the tail and park were a separate power. so now the sending unit from my experience on the GM if it reads full it has a open. if it reads empty it has a short. seldom the gage most often the sending unit or the wiring in the rear going to it.

now if you can tell me why my 68 quits every now and then but restarts right up I'll have my gremlins captured. I'm up to the ignition switch on it now. they no longer make a factory replacement for it.
Click to expand...

Long shot on the 68...bad fuel cap vent?
 
You must log in or register to reply here.
Back
Top