1972T Red Blinking Light Question

[davec]

So my brother brings over a 72T Sportomatic, Sepia Brown (ughh), that his friend inherited. He talks me into helping him get it running (sat for a few years). We get into it and find brittle fuel lines, bad master cylinder, calipers, fuel pump, stuck throttle bodies and a few more "minor" issues. 100 man hours later we started it today and went for the maiden voyage. Great feeling, even if it's not mine;^)

Question: there's a red light on the top of the speedo that won't stop blinking. I checked the oil pressure, oil level guage, temp, hazzard flashers, alternator (light on the bottom) and am out of guesses (and no manual!). So, what is it?

Dave C

[Shaun @ Tru6]

handbrake

[RSTarga]

I think that light goes on also if the master cylinder is bad

[davec]

Master cylinder is new. E-brake is completely off.

[Shaun @ Tru6]

look at your ebrake wiring/switch as a next step.

[HarryD]

I had that happen when the warning switch on the master cyliner failed. Pull the electrical connector from the switch and see if it stops.

Another possibility is that there is a short in the wiring. The light flashes when either the handbrake is activated or the master cylinder switch is activated. In either case, they complete the connection to ground to activate the light.

[tharbert]

If you just changed the master cylinder, you need to reset the pressure safety switch on the MC. The switch is covered by a small rubber boot. You can reset it by pressing the little stem in. It should stay down.

The safety switch will activate when there is a pressure difference between the front and rear circiuts. After resetting the switch, the light should go out. If you step on the brakes and it comes back on, something is wrong.

[HarryD]

Originally Posted by tharbert

If you just changed the master cylinder, you need to reset the pressure safety switch on the MC. The switch is covered by a small rubber boot. You can reset it by pressing the little stem in. It should stay down.

The safety switch will activate when there is a pressure difference between the front and rear circiuts. After resetting the switch, the light should go out. If you step on the brakes and it comes back on, something is wrong.

You know,

I have read this advice a million times but I was unable to find this reset swtich on either my original 1973 switch nor it's replacement. Are you sure you are not talking about a later part?

[tharbert]

The switch was on both the MC I removed and the replacement unit...little white stem under the small rubber boot. I'm pretty sure it was the original 19mm MC. I think I read somewhere that newer units have two-contact switches? Mine has a single contact switch that I imagine goes to ground when it activates. My light was blinking as described in the first post. I researched the problem here, crawled under the car, did the deed, light went out.

[tseybold]

My light blinks as well, it seems the boot cover (Well my boot cover)pushes up just enough to make the contact loose breaking the contact.
Food for thought

[tharbert]

Originally Posted by tseybold

My light blinks as well, it seems the boot cover (Well my boot cover)pushes up just enough to make the contact loose breaking the contact.
Food for thought

I think the switch goes to ground at activation? Maybe experts will chime in here but a broken connection would stop the dash light from blinking.

You may want to look at the p-brake switch adjustment?

[C4 Pazzo]

You may have some air in one of the brake circuits causing a slight pressure differential. If you've reset the MC switch and checked the handbrake switch, try bleeding the brakes some more. It can take a while to get all the bubbles out after changing the MC.

[Shaun @ Tru6]

was the MC bench bled before installation?

[davec]

No, I did not bench-bleed the MC before installation. I knew I was going to rebuild the calipers too, so I didn't bother. And, I have a power bleeder. That's when I found out the overflow line from the reservoir was broken! Blue brake fluid was seeping out of the top of the shock tower. Very freaky.

[john walker's workshop]

try key on, battery disconnect 10 seconds, reconnect, key off, start engine. works for later cars. i don't remember a light on the top of the speedo though, but i'm getting older....