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Topic: High mount works, regular brake lights don't (Read 1438 times) previous topic - next topic

High mount works, regular brake lights don't

Ok, so I have a mess of wiring to fix (tackling all the  I have been doing on my DD, with only weekends to tear apart, mod and reassemble before monday was a bad idea, LOL, I'm gonna get a different DD)...  But my immediate problem is my brake lights.  My high mount stop lamp works fine when I apply the brakes but my actual brake lights do not!  I would have never imagined they would be on separate circuits but apparently they are. 

So, long story short, I just moved and all my diagrams are packed up (I know, convenient)..  anyone know off hand where the brake light signal splits or just where to look to find the cause?
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

High mount works, regular brake lights don't

Reply #2 –
oh god...  LOL  do you have any idea what you're saying to me?!?  :beatyoass: jk, it's ok.  oh man, this could be rough!

Could you explain real quick how the signal gets from the pedal, to the multi func sw and how it is split?  The reason I ask is because I have to then translate it into the thunderbird meets 2002 mustang  multi func sw and wiring...  I think I'm going to need to dig up my diagrams and rebuttstuffyze every connection I made  :punchballs:

It really makes me wonder how long they've been out... but i was tailed by a cop all the way down the hill and over 5-6 speed bumps a week ago.  He didn't pul me over.  must be a new issue!
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

High mount works, regular brake lights don't

Reply #3 –
The T-Bird and Mustang tail light wiring is similar. Power goes from the brake switch to the multifunction switch, where it then goes to the tail lights IF no signal lights are turned on.

If you turn on a signal light, the multifunction switch breaks the circuit to that side and reroutes it through the turn signal flasher, which gives you brake lights on one side and flashing turn signals on the other.
2015 Mustang GT Premium - 5.0, 6-speed, Guard Green - too much awesome for one car

1988 5.0 Thunderbird :birdsmily: SOLD SEPT 11 2010: TC front clip/hood ♣ Body & paint completed Oct 2007 ♣ 3.55 TC rear end and front brakes ♣ TC interior ♣ CHE rear control arms (adjustable lowers) ♣ 2001 Bullitt springs ♣ Energy suspension poly busings ♣ Kenne Brown subframe connectors ♣ CWE engine mounts ♣ Thundercat sequential turn signals ♣ Explorer overhead console (temp/compass display) ♣ 2.25" off-road dual exhaust ♣ T-5 transmission swap completed Jan 2009 ♣

High mount works, regular brake lights don't

Reply #4 –
ok, then I think it's related to the auto lamp problems I've been having (AL turns on headlights always, never markers/tails and I have to manually pull the switch out to get headlights AND markers/tails).  Thanks...  i think my next step will be to temporarily bypass the AL system.
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

High mount works, regular brake lights don't

Reply #5 –
Quote from: booksix;230537
ok, then I think it's related to the auto lamp problems I've been having (AL turns on headlights always, never markers/tails and I have to manually pull the switch out to get headlights AND markers/tails).  Thanks...  i think my next step will be to temporarily bypass the AL system.


The autolamp feature is not involved with the brake lights. Rear running lights yes but not the brake lights.

See pages 94 and 95 in jcassity's 1987 EVTM sticky.

High mount works, regular brake lights don't

Reply #6 –
I know, I guess it was unrelated to everyone here, but in my mind it is related because of some other issues with the entire lighting system and bypassing it will eliminate some extra variables...  Just ignore that last comment, it was me thinking out loud! LOL
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

High mount works, regular brake lights don't

Reply #7 –
Ok, so forget all that... I checked out my autolamp/py alarm issues, no go.

So I resorted to the EVTM (Thanks Scott, my disc is packed up after moving so I used your photobucket evtm!) and I did see where the high mount stop lamp runs straight off the pedal switch.  I also saw where the turn/stop lamps are wired to the multi func sw.  So, my initial thought is that, if the brake lights don't function, the turn/hazards shouldn't either.  But they do...  Ok, bulbs are good, pedal switch is good, multi func sw seems like it should be ok.  Any thoughts were to look next?
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

High mount works, regular brake lights don't

Reply #8 –
It should be simple: The wire between the brake light switch and multifunction switch. Use a test light and probe the multifunction switch harness where the brake light wire is. Push the brake pedal. If the test light lights up you've got power that far and the problem is in the switch itself. If the test light doesn't light up the problem is in the wire (you know the brake light switch is OK because the CHMSL works).
2015 Mustang GT Premium - 5.0, 6-speed, Guard Green - too much awesome for one car

1988 5.0 Thunderbird :birdsmily: SOLD SEPT 11 2010: TC front clip/hood ♣ Body & paint completed Oct 2007 ♣ 3.55 TC rear end and front brakes ♣ TC interior ♣ CHE rear control arms (adjustable lowers) ♣ 2001 Bullitt springs ♣ Energy suspension poly busings ♣ Kenne Brown subframe connectors ♣ CWE engine mounts ♣ Thundercat sequential turn signals ♣ Explorer overhead console (temp/compass display) ♣ 2.25" off-road dual exhaust ♣ T-5 transmission swap completed Jan 2009 ♣

High mount works, regular brake lights don't

Reply #9 –
Ah yes, ok thanks!
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

High mount works, regular brake lights don't

Reply #10 –
ok, yes it was mostly the multi func sw.  Another problem is about 3 of the wires in the connectors at the switch were out and don't stay in (plastic clip inside broken).  Guess that's what happens when you use JY pigtails!
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats