Electrical Issue Sanity Check

[mach1mustang351]

Hey everyone,

I have messed with this for two evenings now and I wanted to run it by some folks to check my sanity.

I am trying to work out some issues with my 1979 1000SP. 

I have no headlights, no High or Lo beams.  The flash setting will turn it on.

I can command the lights on from the switch and from the main harness.  I have power to the On position of the switch when in position 1.

I have dash lights, warning lights and everything else seems to work.

Am I missing something here?? I feel like I have over looked something. 

Any help or ideas appreciated.

Thanks

[rodekyll]

Check headlight ground from the headlight socket. 

I have no idea what this means:  I can command the lights on from the switch and from the main harness.

[mach1mustang351]

I guess I just needed to talk it out and start the diagnostic process over again.

I found a more accurate wiring diagram and started from the basics again.

There is a wire that goes from the ON/OFF/PARK switch that is the power to the HI/LO switch.

There is something wrong with the contact in the ON/OFF switch where it isn't junctioning power to the HI/lo side.

I confirmed via an ohm meter at the switch. There was no connection. I then used my power probe to send power to this wire and the HI/LO functioned and the headlight came on.

I guess i need a new switch.

Thanks for listening.

[mach1mustang351]

Check headlight ground from the headlight socket. 

I have no idea what this means:  I can command the lights on from the switch and from the main harness.

All I meant there was I can apply voltage and get the light to function properly.

[rodekyll]

Got it.

Yes, it's the contacts in the switch.  They may be repairable/serviceable.  We've got some folks here that are pretty sharp on the switches.  I hope they'll be along shortly.  In the meantime you might use the search function to try digging up one of the many discussions on the topic.

[Groover]

I have serviced that same switch on mine because of a similar wonky issue. I don't have photos unfortunately, so I hope this helps.

What I discovered on mine is that the brass plate shaped like a right-angled "U" (it looks like say 1/4" long worth of still attached staples from a small stapler) was worn and not making contact with the multiple points that plate needs to cover. This brass plate slides with the position of the switch and needs to make contact on 2 or more contacts (I think 4 at a time in some positions).

This same brass plate has pressure applied by a tiny spring and a tiny ball. These put the pressure on the plate needed to make the contact and the ball is needed for the "notch" feel between positions - NOTE: The ball is small and can get lost easily. That said, do the disassembly on a nice clear surface and be prepared to catch a tiny ball when taking it apart.

What I did to fix it:

Sanded this brass U shaped plate flat again (it was worn by the contacts leaving grooves), then I put a ~1mm spacer on the non-contact side of the plate between the plate and the ball/spring mechanism to put a little more pressure on the now even thinner plate (after sanding it flat) - that spacer may not be necessary, but I did it anyway. The goal is the get the U shape plate's contact surface flat again without grooves so it can touch the multiple points at once.

I hope that helps. If fixed my issue. My issue extended to the tail light as that is also controlled by one of the contacts on that switch.

Good luck.

[Kiwi_Roy]

Looking at the switch the Red wire brings power from the battery when it's turned On the brown wire takes power back to the fuses. If the brown wire has Voltage on it with the switch On then check the fuses are making good contact in their clips.

Apply a little Vaseline to the contacts of the switch, this lubricates so they don't wear away.
The switch is not protected by a fuse, it's possible to do some real damage if you accidentally short it out so
disconnect the battery negative. As an electrician the lack of a fuse makes me cringe, I like to add a 40 Amp in line.

[pehayes]

I'd like to see a photo of the switch opened up with the brass plate removed.  I'm not sure if the design is the same as found on my '87 SPII.  On mine, the wires all terminate in tiny 'ring' connectors.  These are riveted into the plastic body of the switch with the domed heads of the rivets serving as contacts against the sliding brass plate.  As the system wears and ages, the contact gets poor.  Poor contact = heat.  Heat in a plastic environment = melting.  The plastic body softens. The spring pressure causes the rivet heads to recess into the plastic until they are no longer exposed and no longer make contact.  The tension on the ring terminal ends gets loose.  It is a downhill snowball after that.  I was able to restore mine by replacing the rivet with 2mm threaded bolts and rounding the bolt heads to slide against the brass plate.  Been working reliably for years.

Patrick Hayes
Fremont CA

[Groover]

I'd like to see a photo of the switch opened up with the brass plate removed.  I'm not sure if the design is the same as found on my '87 SPII.  On mine, the wires all terminate in tiny 'ring' connectors.  These are riveted into the plastic body of the switch with the domed heads of the rivets serving as contacts against the sliding brass plate.  As the system wears and ages, the contact gets poor.  Poor contact = heat.  Heat in a plastic environment = melting.  The plastic body softens. The spring pressure causes the rivet heads to recess into the plastic until they are no longer exposed and no longer make contact.  The tension on the ring terminal ends gets loose.  It is a downhill snowball after that.  I was able to restore mine by replacing the rivet with 2mm threaded bolts and rounding the bolt heads to slide against the brass plate.  Been working reliably for years.

Patrick Hayes
Fremont CA

The way you described the contact/ring ends sounds exactly like the ones on my G5.

[mach1mustang351]

I'd like to see a photo of the switch opened up with the brass plate removed.  I'm not sure if the design is the same as found on my '87 SPII.  On mine, the wires all terminate in tiny 'ring' connectors.  These are riveted into the plastic body of the switch with the domed heads of the rivets serving as contacts against the sliding brass plate.  As the system wears and ages, the contact gets poor.  Poor contact = heat.  Heat in a plastic environment = melting.  The plastic body softens. The spring pressure causes the rivet heads to recess into the plastic until they are no longer exposed and no longer make contact.  The tension on the ring terminal ends gets loose.  It is a downhill snowball after that.  I was able to restore mine by replacing the rivet with 2mm threaded bolts and rounding the bolt heads to slide against the brass plate.  Been working reliably for years.

Patrick Hayes
Fremont CA

That describes how they are done on mind. I think the previous bad hands had been into these switches before. The wires were pulled out on the other side. That switch I replaced. This one will likely get replaced, but its fixed for now. Just waiting on the next pieces.