no running or brake lights, completely baffled
#1043610
07/31/11 12:33 AM
07/31/11 12:33 AM
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Joined: May 2003
Posts: 2,414 St. Croix, US Virgin Islands
David_in_St_Croi
OP
top fuel
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OP
top fuel
Joined: May 2003
Posts: 2,414
St. Croix, US Virgin Islands
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I am completely baffled by the latest electrical problem on our 70 RR. Went to the local track but rained out (it is the wet time of year here). Went to leave, turn on lights. Nothing but headlights. Drive home anyway, what else to do. Decided to do some trouble shooting. There are two hot leads to the headlight switch. One is 16 ga, the other is 18 ga (both seem light to me but that is a different discussion). There is 12 volts at each. The 16 ga I think drives the headlights, the 18 ga drives everything else. When I jump from the 16 ga terminal in the connector to the taillight terminal in the connector, the running lights all work. When I jump from the 18 ga one that is supposed to drive the running lights (it comes directly from the fuse block terminal marked stop/tail) nothing. Even the 12 volts go away when it is jumped together. When I use the 16 ga wire to jump I still get 12 volts at the 16 ga wire and the lights work.
To make it more frustrating, the brake lights also do not work. Even if I pull the wires off the brake light switch and jumper them together, no brake lights. There is 12 volts at the wire that is supposed to have it. The turn signals work fine, so I do not think it is the turn signal switch but ???.
I have removed and reinstalled the fuses in the fuse block, so I do not think it is corrosion there but maybe?? I am getting 12 volts but perhaps under load the resistance is too high due to corrosion? We are ground zero for corrosion here.
We have three British cars, all older than the 70 RR. Their electrical systems are 1/8 as complicated (the entire car fits on one page)and work better. This is not the first time I have been tempted to gut the entire electrical system and streamline it with Lucas fittings I can trust.
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Re: no running or brake lights, completely baffled
[Re: David_in_St_Croi]
#1043615
07/31/11 09:53 AM
07/31/11 09:53 AM
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Joined: Nov 2009
Posts: 2,275 Desert Tracker
HYPER8oSoNic
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You say you are at ground zero for corrosion, check your grounds on both the brake and running lights circuits. It's also a possibility that the 18 gauge wire has gone brittle.
"Stupidity is Ignorance on Steroids" "Yeah, it's hopped to over 160" (quote by Kowalski in the movie Vanishing Point 1970 - Cupid Productions)
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Re: no running or brake lights, completely baffled
[Re: HYPER8oSoNic]
#1043616
07/31/11 10:43 AM
07/31/11 10:43 AM
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Joined: May 2003
Posts: 2,414 St. Croix, US Virgin Islands
David_in_St_Croi
OP
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OP
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Joined: May 2003
Posts: 2,414
St. Croix, US Virgin Islands
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Thanks for all the help so far. Grounds are good I believe, I have a separate ground wire for the taillight assemblies that fixed a problem a couple years ago. When I hook up to the wire that feeds the headlight source the lights all work, which is why I think the grounds are okay in this case. I agree with a couple of posters, I will have to start cleaning contacts, probably start with the fuses, although I have removed and reinstalled them which will frequently improve the contact enough for a circuit to work. This portion of the harness is all original so as mentioned maybe the feed wire itself is bad and will show 12 volts with a multimeter but as soon as a load is on it the resistance is too high (this could also apply to a connection of course). It really is amazing the gauge of wire the factories used when these were new. I agree grounds (or the lack of) can cause some baffling problems so I will explore that but I think in this case it must be on the feed (hot) side but ....
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Re: no running or brake lights, completely baffled
[Re: David_in_St_Croi]
#1043618
07/31/11 07:59 PM
07/31/11 07:59 PM
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Joined: Nov 2009
Posts: 2,275 Desert Tracker
HYPER8oSoNic
top fuel
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top fuel
Joined: Nov 2009
Posts: 2,275
Desert Tracker
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Quote:
Thanks for all the help so far.
Grounds are good I believe, I have a separate ground wire for the taillight assemblies that fixed a problem a couple years ago.
When I hook up to the wire that feeds the headlight source the lights all work, which is why I think the grounds are okay in this case.
I agree with a couple of posters, I will have to start cleaning contacts, probably start with the fuses, although I have removed and reinstalled them which will frequently improve the contact enough for a circuit to work.
This portion of the harness is all original so as mentioned maybe the feed wire itself is bad and will show 12 volts with a multimeter but as soon as a load is on it the resistance is too high (this could also apply to a connection of course).
It really is amazing the gauge of wire the factories used when these were new.
I agree grounds (or the lack of) can cause some baffling problems so I will explore that but I think in this case it must be on the feed (hot) side but ....
Could be a combination of both, electrical circuits ARE tricky. However the feed wire may have an open spot/bad connection or "fracture" due to age/corrosion.
"Stupidity is Ignorance on Steroids" "Yeah, it's hopped to over 160" (quote by Kowalski in the movie Vanishing Point 1970 - Cupid Productions)
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Re: no running or brake lights, completely baffled
[Re: macmic87]
#1043622
07/31/11 10:03 PM
07/31/11 10:03 PM
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Joined: Nov 2005
Posts: 836 lancaster, new york
macmic87
super stock
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super stock
Joined: Nov 2005
Posts: 836
lancaster, new york
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Quote:
just my guess, but it sounds like there is high resistance that has developed in the circuit with the 18 gauge wire. with the high resistance with no load (just checking for voltage) you will show 12 volts. as soon as the load is applied (connecting to running lights) the voltage wil drop and lights won't work. using the wiring diagram start checking the connections from the batttery back. maybe even the simple act of disconnecting and reconnectiong a connection will clean it enough to make it work better. even remove fuse and check condition of connectors.
Quote:
Anyway, the problem seems to have been high resistance in the supply wire for those circuits to the fuse box due to corrosion/deterioration in the removable female spade terminal.
holy cow i got one right!!
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Re: no running or brake lights, completely baffled
[Re: MoparforLife]
#1043624
08/01/11 01:14 AM
08/01/11 01:14 AM
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Joined: Jan 2003
Posts: 21,507 N.E. OHIO, USA
A12
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 21,507
N.E. OHIO, USA
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Quote:
I sure don't remember the park lights being on with the headlights as early as 1970. Could be but i sure didn't think so. I was thinking that it was quite a bit later than that.
'68 B-body or at least a '68 road runner did not run the front parking/running lights when the headlights were turned on but the '69's did. The only thing that I found when I was trying to figure out if I had a '68 or '69 underdash wiring harness was one yellow wire on the '68 that shut off the front parking lights and I think that's because the '68's had four (4) side marker lights that may have (by engineering standards???) been determined to be too much draw with the headlights or high beams on?????? "69 models had four (4) reflectors and did away with the four side marker lights.
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Re: no running or brake lights, completely baffled
[Re: A12]
#1043625
08/01/11 01:19 AM
08/01/11 01:19 AM
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Joined: Jan 2003
Posts: 21,507 N.E. OHIO, USA
A12
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 21,507
N.E. OHIO, USA
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