Doing a little more work on the Plymouth. Part Two
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| My hand drawn wiring diagram. |
As I mentioned in my last post, I had experienced a brake problem and was expecting to find a noticeable leak in the system. I did not find any leaking, however the problem could have been caused by an internal leak in the master cylinder.
I had parked the car in the garage after I got back from that drive, and became busy with other matters. So it sat for almost three months. After I replaced the battery and backed it out of the garage, I decided to drive it around the neighborhood a bit. On this drive I didn't have a problem with the brakes. But when I got back and checked the brake lamps they were really dim. Not good.
To check the operation of the stop lamps, I disconnected the wires at the switch, and connected them together with a jumper wire. I could clearly see the CHMSL light up, and I went around the back and saw the trunk mounted brake lamp brightly lit. I left the jumper on for a few minutes and felt the brake switch, it did feel a bit warm.
I needed to do a test to see if there was an internal leak inside the master cylinder. This would also show if the switch was heating up.
I decided that I would fully apply the brake pedal for a full five minutes. I would find out if the pedal would sink towards the floor over time. I could also check the brake switch and see if it was heating up. I got my stop watch and pushed hard on the pedal. Five minutes later it had not budged a bit, Then I quickly got out and felt the stop light switch. It was pretty hot! I wondered if I'd burnt it out.
I needed to check it.
First I disconnected the battery, then I connected my multi meter to the terminals of the brake switch, it was set to indicate continuity. I pressed on the brake pedal and heard the buzzer sound, so the switch still worked. Then I re-connected the battery and connected the input power terminal and hooked up my multimeter to measure voltage. I used a couple of long jumper wires so that I could position the meter where I could see it while I was in the car pressing on the brake pedal. The meter indicated a bit over six volts. I figured that it was probably enough to switch the relay system that I was going to add.
I had ordered a couple of relays earlier this Summer, so I already had them on hand. I went to a couple of local Auto parts stores and bought wire, connectors, and a terminal block. Wire has gotten to be pretty expensive lately.
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| This is how I set up the relays for the headlamps on my '70 Mustang. It worked like a charm. |
Then I looked online for info on how to hook them up. I had previously used relays on the headlamp wiring of my '66 Mustang. So I was familiar with how to hook them up, but it had been awhile. I drew a diagram showing how to hook up the wires to the relay, and it also showed how the wires were going to be run in the car.
I put this diagram in my Plymouth's owner's manual for later reference.
Brake lamps usually have constant power on most cars, so I decided to hook the circuit to the hot side of the starter solenoid. I would run a 10 gauge wire through the firewall to a terminal block under the dash. Then I would run a 12 gauge wire to the trunk compartment where I would install the relay and connect it to the original brake light, as well as connect it to the wires of the CHMSL that I'd added.
| The second wire will be in place if I need it. Maybe to connect the heater that I might install later. |
I added a 30 amp fuse to the power feed then ran the wire to the terminal block that I attached to the radio box. I also added an additional 10 gauge wire so that I had two wires going to the terminal block, but the extra wire was not connected at either end. I might want to wire up a heater in the future so it would be in place if needed.
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| Plenty of room inside the trunk to work comfortably. |
| Afterwards I went back and tidied up the job and put some sheathing around the new wires. |
By placing the relay in the trunk I only had to run a single wire from the junction block. If I had wired it under the hood, I'd have to run at least two wires. I added an inline 20 amp fuse before the relay, and I ran a new wire from the relay to the original brake lamp. I had thought that the wire that had been used when it was rewired was a bit thin for the job.
The additional circuit was run independently from the existing harness. I did not want to start messing with the existing wiring. It might not be a perfect job, but it has worked fine for many, many, years.
The existing brake light switch worked out quite well and with direct power, the brake lamps were really bright! I felt that these would be easy to notice, and that would add a lot of safety.
| Much better! |
Now, I'll turn my attention to the inoperative ratchet mechanism on the hand brake lever.



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