122s overdrive problems

[Damoyorkie]

Dear All,

I’ve just rewired the youngest lad’s overdrive.

A horrible switch on the dash has been replaced with the proper switch on the steering column. I had to replace the dash switch with a green Halfords lamp.

We took the car out for a drive night and noticed the overdrive was dropping out when on the main beam.

I’ve checked the oil level of the gearbox/overdrive and we have had to put just under a litre of 20w50 oil into the gearbox filler (which was done with a 5cc syringe, as I’d lost my oil can). So the levels are good and it’s full of oil.

Having taken it out and given it a good run, it drops out mainly whenever there is an electrical load put on it, i.e. it drops out whenever it’s in overdrive with headlights on, and the indicators or main beam is operated.

Any ideas as to what I’ve done wrong ? Photos of the wiring as it was and as it is have been attached.

Cheers

Damien

[JP 1800]

There are no pics attached, if the OD is dropping out when a load is placed on the electrical system I would first look at the fuse box for corrosion and any forms of electrical resistance. You should measure the voltage drop across the fuse box and connections going to the OD solenoid to ascertain how much of a drop is measured. I would also do likewise for the headlamps. Lastly is the OD solenoid connected to a relay or directly wired to the switch?

[Ron Kwas]

Damo;

OD Sol should be independent of other loads on elec sys, but if it acts as if associated with other loads, that suggests a Voltage Drop typically caused by an in-line resistance due to a poor connection or corrosion as JP mentions, can be the cause.

If OD is connected as it should be for a 122 or 123, as shown here, supplied from Fuse 1: https://www.sw-em.com/123GT-Wiring-Diagram_US.jpg (see items: 18, 19, 25, with 35 being the switch), I'd double-check wiring, and measure voltage supplied vs voltage at Sol when activating those loads that seem to affect it and cause it to drop out (this strongly suggests an interaction due to supply VD), and I have explained this here: https://www.sw-em.com/electical_circuit_interaction.htm [See: Power Side Inadvertent Circuit Interaction and Figure 1.].

...so the solution is to locate and minimize VD (start with all Ign Power connections, from Ign Sw term 54, to Fuse 1, also low side[chassis connection of OD Control Sw 35])...alternately, supplying the OD circuit from Ign Power terminal 54 of Ign Sw, with its own dedicated Fuse.

Good Hunting!

[Damoyorkie]

Many thanks JP and Ron.

You are legends both.

He’s away back to Scotland tomorrow first thing, taking the Amazon with him, so I’ll check the corrosion first thing, but probably won’t have the time to check the voltage drops.

When he’s back at Christmas I can have a little tinker.

Cheers once again chaps.


Damien